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april 2004 1 m9999-042204 mic2593 micrel mic2593 dual-slot pci hot plug controller general description the mic2593 is a power controller supporting power distribu- tion requirements for peripheral component interconnect hot plug systems compliant to pci v2.3 and pci-x 1.0b. the mic2593 provides complete power control support for two pci slots, including the 3.3v aux defined by the pci v2.3 specification. support for +5v, +3.3v, +12v, and ?2v sup- plies is provided and includes programmable current limit, voltage supervision, fault reporting, and circuit breaker func- tions which provide fault isolation. the mic2593 also incor- porates an smbus interface that provides complete status and control of power within each slot. micrel, inc. ?1849 fortune drive ?san jose, ca 95131 ?usa ?tel + 1 (408) 944-0800 ?fax + 1 (408) 474-1000 ?http://www.mic rel.com features supports two completely independent pci slots: - compliant to pci v2.3 and pci-x 1.0b power control requirements - provides all major power control functions for two independent pci-x 2.0 slots five voltage supplies supported: +12v, -12v, +5v, +3.3v, and +3.3v aux - integrated gate driver circuits, current sense, and power mosfets for 3.3v aux , +12v, and ?2v - high-side +5v and +3.3v gate driver circuits for external n-channel mosfets overcurrent protection with adjustable timeout elimi- nates false tripping of circuit breakers dual-level, dual-speed overcurrent detection circuitry for quick fault response without nuisance tripping slot power control with ?ower-is-good?and fault status reporting - via software over an smbus interface or - via dedicated hardware input/output lines: hot plug interface (hpi) complete thermal isolation between circuitry for slot a and slot b one general purpose input (gpi) pin per slot for mechanical switch or plug-in card retention/removal input applications pci hot plug power distribution ideal applications: mid- and high-end server applications compliant to pci v2.3, pci-x 1.0b, and pci-x 2.0 ordering information 5v & 3v fast-trip +12v & ?2v fast-trip part number threshold threshold operating temp. range package MIC2593-2BTQ 100mv 1.5a/0.4a 0 c to +70 c 48-pin tqfp mic2593-5btq disabled* 1.5a/0.4a 0 c to +70 c 48-pin tqfp *contact factory for availability. little foot is a registered trademark of siliconix incorporated .
mic2593 micrel m9999-042204 2 april 2004 typical application pci connector vstbyb vstbya vauxa 5vina 5vsensea 3vina 3vsensea 5vinb 5vsenseb 3vinb 3vsenseb 5vgatea 5vouta 3vgatea 3vgateb 3voutb 12voutb 12mvoutb vauxb 3vouta 12vouta 12mvouta gnd gnd a1 a2 a0 onb ona gpib gpia auxenb auxena /int scl sda 5vgateb 5voutb cfiltera cfilterb mic2593 *r 12vgatea 15 ? si4420dy si4420dy c gate 0.01 f 0.01 f 15 ? r sense 0.008 ? pci bus 3.3auxa 375ma 3.3v, 7.6a 12v, 0.5a 12v, 0.1a 5v, 5a r sense 0.008 ? *r 12vgateb 15 ? si4420dy 0.01 f r sense 0.005 ? si4420dy c gate 0.01 f *r 3vgateb r sense 0.005 ? pci connector pci bus 3.3auxb 3.3v, 7.6a 5v, 5a * values for r 5vgate[a/b] and r 3vgate[a/b] may vary depending upon the c gs of the external mosfets. ** values determined by design requirements. see functional description section for detailed information. # mbrs140t3 or equivalent is recommended. bold lines indicate high current paths 4 2 11 26 6 7 8 9 12 13 14 16 10 19 31 30 29 28 25 24 23 21 22 12v, 0.1a 20 12v, 0.5a 27 33 46 15 15 ? *r 3vgatea 0.1 f 0.1 f 0.1 f 0.1 f 0.1 f 0.1 f 0.1 f 0.1 f 0.1 f /faultb /faulta 1 /int scl sda smbus i/o management controller 48 47 37 43 42 38 35 45 44 v stby **c1 **c2 v stby 10k 3 10k 4 10k 2 sda scl /int smbus base address 39 40 41 gpib 100k 100k gpia v stby 12vslewa 12vslewb 3 34 **c3 **c4 36 v stby 532 1718 power supply +12v 12v +5.0v +3.3v vstby # schottky diode (clamp) 12vina 12vinb 12mvina 12mvinb onb ona auxenb auxena hot plug controller /faultb /faulta
april 2004 3 m9999-042204 mic2593 micrel pin configuration 48-pin tqfp 12mvina 3vouta vauxa 3vgatea 3vsensea 12mvinb 12mvouta 12mvoutb /faulta cfiltera 12vslewa gpia 12vina 5vina 5vsensea 5vgatea 13 14 15 16 17 18 19 20 1 2 3 4 5 6 7 8 5vouta 12vouta vstbya 3vina 9 10 11 12 3voutb vauxb 3vgateb 3vsenseb 21 22 23 24 /faultb cfilterb 12vslewb gnd 12vinb 5vinb 5vsenseb 5vgateb 36 35 34 33 32 31 30 29 5voutb 12voutb vstbyb 3vinb 28 27 26 25 ona auxena gnd scl sda onb auxenb a0 48 47 46 45 44 43 42 41 a1 a2 gpib /int 40 39 38 37 hot plug control interface slot a interface slot b interface
mic2593 micrel m9999-042204 4 april 2004 pin description pin number pin name pin function 5 12vina +12v supply power [a/b]: pin 5 is the input to the drain side of the internal 32 12vinb mosfet switch for +12v slot a. pin 32 is the input to the drain side of the internal mosfet switch for +12v slot b. these two pins must ultimately connect to each other within 10 cm of the mic2593. an undervoltage lockout circuit (uvlo) prevents the switches from turning on while this input is less than its lockout threshold. 10 12vouta +12v output [a/b]: pin 10 is connected to the source terminal of the internal 27 12voutb mosfet switch for +12v slot a and pin 27 is connected similarly for slot b. 17 12mvina 12v supply power [a/b]: pin 17 is the input to the drain side of the internal 18 12mvinb mosfet switch for +12v slot a. pin 18 is the input to the drain side of the internal mosfet switch for 12v slot b. these two pins must ultimately connect to each other within 10 cm of the mic2593. an undervoltage lockout circuit (uvlo) prevents the switches from turning on while this input is less than its lockout threshold. 19 12mvouta 12v output [a/b]: pin 19 is connected to the source terminal of the internal 20 12mvoutb mosfet switch for 12v slot a and pin 20 is connected similarly for slot b. 3 12vslewa 12v slew rate control [a/b]: connect capacitors between these pins and 34 12vslewb ground to set the output slew rates of the +12v and 12v supplies. see the functional description section for more details. 6 5vina 5v supply power and sense input [a/b]: pin 6 is the (+) kelvin-sense 31 5vinb connection to the supply side of the sense resistor for 5v slot a. pin 31 is the (+) kelvin sense connection to the supply side of the sense resistor for 5v slot b. these two pins must ultimately connect to each other within 10 cm of the mic2593. an undervoltage lockout circuit (uvlo) prevents the switches from turning on while this input is less than its lockout threshold. 7 5vsensea 5v circuit breaker sense input [a/b]: the current limit thresholds are set 30 5vsenseb by connecting sense resistors between these pins and 5vin[a/b]. when the current limit threshold of ir = 50mv is reached, the 5vgate[a/b] pin is modulated to maintain a constant voltage across the sense resistor and therefore a constant current into the load. if the 50mv threshold is exceeded for t flt (see cfilter[a/b] pin description), the circuit breaker is tripped and the gate pin for the affected supply s external mosfet is immediately pulled low. 9 5vouta 5v power-good sense inputs: connect to 5v[a/b] outputs. used to 28 5voutb monitor the 5v output voltages for power-is-good status. 8 5vgatea 5v gate drive output [a/b]: each pin connects to the gate of an external 29 5vgateb n-channel mosfet. during power-up, the c gate and the c gs of the mosfets are charged by a 25 a current source. this controls the value of dv/dt seen at the source of the mosfets, and hence the current flowing into the load capacitance. during current-limit events, the voltage at the pin is adjusted to maintain constant current through the switch for a period of t flt . whenever an overcurrent, thermal shutdown, or input undervoltage fault condition occurs, the gate pin for the affected slot is immediately brought low. during power-down, these pins are discharged by an internal current source. 12 3vina 3.3v supply power and sense input [a/b]: pin 12 is the (+) kelvin-sense 25 3vinb connection to the supply side of the sense resistor for 3.3v slot a. pin 25 is the (+) kelvin-sense connection to the supply side of the sense resistor for 3.3v slot b. these two pins must ultimately connect to each other within 10 cm of the mic2593. an undervoltage lockout circuit (uvlo) prevents the switches from turning on while this input is less than its lockout threshold.
april 2004 5 m9999-042204 mic2593 micrel pin description (cont) pin number pin name pin function 13 3vsensea 3v circuit breaker sense input [a/b]: the current limit thresholds are set by 24 3vsenseb connecting sense resistors between these pins and 3vin[a/b]. when the current limit threshold of ir = 50mv is reached, the 3vgate[a/b] pin is modulated to maintain a constant voltage across the sense resistor and therefore a constant current into the load. if the 50mv threshold is exceeded for t flt (see cfilter[a/b] pin description), the circuit breaker is tripped and the gate pin for the affected supply s external mosfet is immediately pulled low. 16 3vouta 3.3v power-good sense inputs: connect to 3.3v[a/b] outputs. used to 21 3voutb monitor the 3.3v output voltages for power-is-good status. 14 3vgatea 3v gate drive output [a/b]: each pin connects to the gate of an external 23 3vgateb n-channel mosfet. during power-up, the c gate and the c gs of the mosfets are connected to a 25 a current source. this controls the value of dv/dt seen at the source of the mosfets, and hence the current flowing into the load capacitance. during current limit events, the voltage at this pin is adjusted to maintain constant current through the switch for a period of t flt . whenever an overcurrent, thermal shutdown, or input undervoltage fault condition occurs, the gate pin for the affected slot is immediately brought low. during power down, these pins are discharged by an internal current source. 11 vstbya 3.3v standby input voltage: required to support pci vaux output. 26 vstbyb additionally, the smbus logic and internal registers run off of vstby[a/b] to ensure that the mic2593 is accessible during standby modes. a uvlo circuit prevents turn-on of this supply until vstby[a/b] rises above its uvlo threshold. both pins must be connected together externally at the ic. 15 vauxa 3.3vaux[a/b] output to pci card slot: these outputs connect 22 vauxb the 3.3aux pin of the pci connectors to vstby[a/b] via internal 400m ? mosfets. these outputs are current limited and protected against short-circuit faults. 44 ona enable inputs: rising-edge triggered. used to enable or disable the maina 43 onb and mainb (5v, 3.3v, +12v and 12v) outputs. taking on[a/b] low after a fault resets the 5v, 3.3v, +12v and/or 12v fault latches for the affected slot. tie these pins to gnd if using smi power control. also, see pin description for /faulta and /faultb. 45 auxena enable inputs: rising-edge triggered. used to enable or disable vauxa and 42 auxenb vauxb outputs. taking auxen[a/b] low after a fault resets the respective slot s aux output fault latch. tie these pins to gnd if using smi power control. also, see pin description for /faulta and /faultb. 2 cfiltera overcurrent timer (filter) capacitor [a/b]: capacitors connected between 35 cfilterb these pins and gnd set the duration of t flt . t flt is the amount of time for which a slot remains in current limit before its circuit breaker is tripped. 1 /faulta /fault[a/b] outputs: open-drain, active-low. asserted whenever the 36 /faultb circuit breaker trips due to a fault condition (overcurrent, input undervoltage, overtemperature). each pin requires an external pull-up resistor to vstby. bringing the slot s on[a/b] pin low resets /fault[a/b] if /fault[a/b] was asserted in response to a fault condition on one of the slot s main outputs (5v, 3.3v, +12v, or 12v). /fault[a/b] is reset by bringing the slot s auxen[a/b] pin low if /fault[a/b] was asserted in response to a fault condition on the slot s v aux output. if a fault condition occurred on both the main and vaux[a/b] outputs of the same slot, then both on[a/b] and auxen[a/b] must be brought low to de-assert the /fault[a/b] output.
mic2593 micrel m9999-042204 6 april 2004 pin description (cont) pin number pin name pin function 4 gpia general purpose inputs: the states of these two inputs are available by 38 gpib reading the common status register, bits [4:5]. if not used, connect each pin to gnd. 40 a1 smbus address select pins: connect to ground or leave open in order to 41 a0 program device smbus base address. these inputs have internal pull-up a0 resistors to vstby[a/b]. 48 sda smbus data: bidirectional smbus data line. 47 scl smbus clock: input. 37 /int interrupt output: open-drain, active-low. asserted whenever a power fault is detected if the intmsk bit (cs register bit d[3]) is a logical "0". this output is de-asserted by performing an "echo reset" to the appropriate fault bit(s) in the stat[a/b] and/or cs registers. this pin requires an external pull-up resistor to v stby . 33 gnd ic ground connections: tie directly to the system s analog ground 46 plane directly at the device.
april 2004 7 m9999-042204 mic2593 micrel absolute maximum ratings (1) supply voltage 12vin ...................................................................... +14v 12mvin ................................................................... 14v 5vin .......................................................................... +7v 3vin, vstby ............................................................ +7v any logic pin ............................................ 0.5v to 3.6v output current (/fault[a/b], /int, sda) .................. 10ma lead temperature ir reflow, peak temperature ................... 240 0 c/ 5 c storage temperature ............................... 65 c to +150 c esd rating (3) human body model ................................................... 2kv machine model ........................................................ 200v operating ratings (2) supply voltage 12vin ................................................ +11.65v to +12.6v 12mvin ............................................... 11.0v to 13.2v 5vin .................................................... +4.85v to +5.25v 3vin ........................................................ +3.1v to +3.6v vstby .................................................. +3.15v to +3.6v ambient temperature (t a ) ............................. 0 c to +70 c junction temperature (t j ) ........................................ 125 c package thermal resistance tqfp ( ja ) ....................................................... 56.5 c/w electrical characteristics (4) 12v in[a/b] = 12v, 12mv in[a/b] = 12v, 5v in[a/b] = 5v, 3v in[a/b] = 3.3v; v stby[a/b] = 3.3v, t a = 25 c; unless otherwise noted. bold indicates specification applies over the full operating temperature range from 0 c to +70 c. symbol parameter condition min typ max units power control and logic sections i cc12v supply currents 0.6 2.0 ma i cc5v 1.2 2.0 ma i cc3.3v 0.5 0.7 ma i cc12mv 1.0 2.0 ma i ccvstby 2.5 5.0 ma undervoltage lockout thresholds v uvlo(12v) 12vin[a/b] 12v in increasing 8 9 10 v v uvlo(3v) 3vin[a/b] 3v in increasing 2.2 2.5 2.75 v v uvlo(5v) 5vin[a/b] 5v in increasing 3.7 4.0 4.3 v v uvlo(12mv) 12mvin[a/b] 12mv in decreasing 10 9 8 v v uvlo(stby) vstby[a/b] v stby increasing 2.8 2.9 3.0 v v hysuv undervoltage lockout hysteresis 180 mv 12vin, 12mvin, 5vin, 3vin v hysstby undervoltage lockout hysteresis 50 mv vstby power-good undervoltage threshold v uvth(12v) 12vout[a/b] 12v out [a/b] decreasing 10.2 10.5 10.8 v v uvth(12mv) 12mvout[a/b] 12mv out [a/b] increasing 10.8 10.6 10.2 v v uvth(3v) 3vout[a/b] 3v out [a/b] decreasing 2.7 2.8 2.9 v v uvth(5v) 5vout[a/b] 5v out [a/b] decreasing 4.4 4.5 4.7 v v uvth(vaux) vaux[a/b] v aux [a/b] decreasing 2.7 2.8 2.9 v v hyspg power-good detect hysteresis 30 mv v gate 5vgate/3vgate voltage 12v in -1.5 12v in v i gate(source) 5vgate/3vgate charge start cycle 15 25 35 a current i gate(sink) 5vgate/3vgate sink current any fault condition 70 ma (fault off) v gate = 5v v filter cfilter threshold voltage 1.20 1.25 1.30 v i filter cfilter[a/b] charge current v 5vin[a/b] v 5vsense[a/b] > v thilimit 1.80 2.5 5.0 a v 5vin[a/b] v 5vsense[a/b] > v thilimit i slew 12vslew[a/b] charge current during turn-on only 13 22 35 a notes: 1. exceeding the absolute maximum ratings may damage the device. 2. the device is not guaranteed to function outside its operating ratings. 3. devices are esd sensitive. employ proper handling precautions. human body model, 1.5k ? in series with 100pf. 4. specification for packaged product only. and/or
mic2593 micrel m9999-042204 8 april 2004 electrical characteristics (continued) (5) symbol parameter condition min typ max units v thilimit current limit threshold voltage 5v[a/b] supplies v 5vin[a/b] v 5vsense[a/b] 35 50 65 mv 3.3v[a/b] supplies v 3vin[a/b] v 3vsense[a/b] 35 50 65 mv v thfast fast-trip current limit thresholds 5v[a/b] and 3v[a/b] MIC2593-2BTQ 90 113 135 mv mic2593-5btq d isabled i 5vsense[a/b] 5vsense[a/b] input current v 5vin[a/b] v 5vin[a/b] = 50mv (6) 0.5 a i 3vsense[a/b] 3vsense[a/b] input current v 3vin[a/b] v 3vin[a/b] = 50mv (6) 0.5 a v il low-level input voltage 0.8 v on[a/b], auxen[a/b], gpi[a/b], scl, sda, a[0-2] v ol output low voltage i ol = 3ma 0.4 v /fault[a/b], /int, sda v ih high-level input voltage 2.1 v on[a/b], auxen[a/b], gpi[a/b], scl, sda, a[0-2] r pull-up internal pullups from a[0-2] to v stby 40 k ? i lkg,off(12vin[a/b]) 12vin[a/b] input leakage current v stby[a/b] = +3.3v 1 a 12v in[a/b] = off (6) i lkg,off(12mvin[a/b]) 12mvin[a/b] input leakage current v stby[a/b] = +3.3v 60 a 12mv in[a/b] = off (6) i lkg,off(5vin[a/b]) 5vin[a/b] input leakage current v stby[a/b] = +3.3v 200 a 5v in[a/b] = off (6) i lkg,off(3vin[a/b]) 3vin[a/b] input leakage current v stby[a/b] = +3.3v 1 a 3v in[a/b] = off (6) i il input leakage current 5 a scl, on[a/b], auxen[a/b], gpi[a/b] i lkg(off) off-state leakage current 5 a sda, /fault[a/b], /int t ov overtemperature shutdown & reset t j increasing, each slot (7) 140 c thresholds, with overcurrent on slot t j decreasing, each slot (7) 130 c overtemperature shutdown & reset t j increasing, both slots (7) 160 c thresholds, all other conditions t j decreasing, both slots (7) 150 c (all outputs will latch off) output mosfet resistance r on(12v) +12v mosfet i ds = 500ma, t j = 125 c 500 m ? r on(12mv) 12v mosfet i ds = 100ma, t j = 125 c 2 ? r on(aux) vaux mosfet i ds = 375ma, t j = 125 c 400 m ? off-state output offset voltage v off(12v) 12vout[a/b] 12v out [a/b] = off, t j = 125 c 50 mv v off(12mv) 12mvout[a/b] 12mv out [a/b] = off, t j = 125 c 50 mv v off(vaux) vaux[a/b] v aux [a/b] = off, t j = 125 c 50 mv current limit slow trip threshold i lim(12v) +12v mosfet 12v out [a/b] = 0v 0.52 1.0 1.5 a i lim(12mv) 12v mosfet 12mv out [a/b] = 0v 0.11 0.2 0.3 a current limit fast-trip threshold MIC2593-2BTQ i fastlim(12v) +12v mosfet 12v out [a/b] 1.0 2.15 3.0 a i fastlim(12mv) 12v mosfet 12mv out [a/b] 0.20 0.45 0.6 a notes: 5. specification for packaged product only. 6. schottky diode clamp used for 12vin[a/b] power bus. see the typical applications circuit. 7. parameters guaranteed by design. not 100% production tested.
april 2004 9 m9999-042204 mic2593 micrel electrical characteristics (continued) (8) symbol parameter condition min typ max units i aux(thresh) auxiliary output current limit threshold current which must be drawn from v aux 0.84 a figure 4 to register as a fault i sc(tran) maximum transient short circuit current v aux enabled, then grounded i max = v stby / r ds(aux) a i lim(aux) regulated current after transient from end of i sc(tran) to c filter time out 0.375 0.7 1.35 a output discharge resistance r dis(12v) 12vout[a/b] 12v out[a/b] = 6.0v 1600 ? r dis(12mv) 12mvout[a/b] 12mv out[a/b] = 6.0v 600 ? r dis(3v) 3vout[a/b] 3v out[a/b] = 1.65v 150 ? r dis(5v) 5vout[a/b] 5v out[a/b] = 2.5v 150 ? r dis (vaux) vaux[a/b] v aux[a/b] = 1.65v 430 ? t off(3v) current limit response time mic2593-2 1 s t off(5v) for 3.3v and 5v outputs, figure 2 c gate = 10nf, v in v sense = 200mv t sc(tran) v aux current limiter response time, v aux[a/b] = 0v (9) 33 s figure 5 t off(12v) 12v current limit response, 12v out[a/b] = 0v (9) 1 s figure 3 t off(12mv) 12v current limit response, 12mv out[a/b] = 0v (9) 1 s figure 3 t prop(3vfault) delay from 3v[a/b] overcurrent limit mic2593-2 1 s to fault output v sense v thlimit = 200mv c filter = 0 t prop(5vfault) delay from 5v[a/b] overcurrent limit mic2593-2 1 s to fault output v sense v thlimit = 200mv c filter = 0 t w on[a/b], auxen[a/b] pulse width note 9 100 ns t por mic2593 power-on reset time note 9 500 s after v stby becomes valid smbus timing (9) t 1 scl (clock) period figure 1 2.5 s t 2 data in set-up time to scl high figure 1 100 ns t 3 data out stable after scl low figure 1 300 ns t 4 data low set-up time to start condition, figure 1 100 ns scl low t 5 data high hold time after stop condition, figure 1 100 ns scl high notes: 8. specification for packaged product only. 9. parameters guaranteed by design. not 100% production tested.
mic2593 micrel m9999-042204 10 april 2004 timing diagrams t 1 t 4 scl sda data in sda data out t 2 t 5 t 3 figure 1. smbus timing 6v 12vgate v thfast v thlimit t off12 figure 2. 12v current limit response timing 1v 3vgate v thfast v thlimit t off3 figure 3. 3v current limit response timing 0 amps i out(aux) i out(aux) i lim(aux) must trip may not trip i aux(thresh) figure 4. v aux current limit threshold 0 amps i out(aux) t sc(tran) i lim(aux) i sc(tran) figure 5. v aux current limit response timing
april 2004 11 m9999-042204 mic2593 micrel mic2593 a2 /int sda scl a0 v stby a1 100k 47 48 37 39 40 41 100k disabling smi when hpi control is used disabling hpi when smi control is used 100k / int auxena auxenb ona onb mic2593 45 42 44 43 figure 6. input pin configuration for disabling hpi/smi control functional description hot swap insertion when circuit boards are inserted into systems carrying live supply voltages ( hot-plugged ), high inrush currents often result due to the charging of bulk capacitance that resides across the circuit board s supply pins. this transient inrush current can cause the system s supply voltages to tempo- rarily go out of regulation, causing data loss or system lock-up. in more extreme cases, the transients occurring during a hot plug event may cause permanent damage to connectors or on-board components. the mic2593 addresses these issues by limiting the inrush currents to the load (pci board), and thereby controlling the rate at which the load s circuits turn-on. in addition to this inrush current control, the mic2593 offers input and output voltage supervisory functions and current limiting to provide robust protection for both the system and circuit board. system interface the mic2593 employs two system interfaces: the hardware hot plug interface (hpi) and the system management inter- face (smi). the hpi includes on[a/b], auxen[a/b], as well as /fault[a/b]; the smi consists of sda, scl, and /int, whose signals conform to the levels and timing of the smbus specification. the mic2593 can be operated exclusively from the smi, or can employ the hpl for power control while continuing to use the smi for access to all but the power control registers. in addition to the basic power control features of the mic2593 accessible by the hpi, the smi also gives the host access to the following information from the part: fault conditions occurring on each supply gpi[a/b] pin status when using the system management interface for power control, do not use the hot plug interface. conversely, when using the hot plug interface for power control, do not execute power control commands over the system management interface bus (all other register accesses via the smi bus remain permissible while in the hpi control mode). when utilizing the smi exclusively, the hpi input pins on[a/b] and auxen[a/b] should be tied to ground as shown below in figure 6 (disabling hpi when smi control is used). this configuration safeguards the power slots in the event that the smbus communication link is disconnected for any reason. additionally, when utilizing the hpi exclusively, the smbus (or smi) will be inactive if the input pins (sda, scl, a0, a1, and a2) are configured as shown in figure 6 below (disabling smi when hpi control is used). power-on reset and power cycling the mic2593 utilizes vstby[a/b] as the main supply input source. vtsby[a/b] is required for proper operation of the mic2593 smbus interface and registers and must be applied at all times. a power-on reset (por) cycle is initiated after vstby[a/b] rises above its uvlo threshold and remains valid at that voltage for 500 s. all internal registers are cleared after por. if vstby[a/b] is recycled, the mic2593 enters a new power-on reset cycle. vstby[a/b] must be the first supply input applied followed by the main supply inputs of 12v in , 12mv in , 5v in , and 3v in . the main supply inputs may be applied in any order. the smbus is ready for access at the end of the por interval (500 s after vstby[a/b] is valid). all outputs remain off during t por . power-up cycle when a slot is off, the 5vgate and 3vgate pins are held low with an internal pull-down current source. when a slot s main outputs are enabled by applying a rising-edge signal at the on[a/b] control input and all input voltages are above their respective undervoltage lockout thresholds, all four main supplies will then execute a controlled turn on. the 5vgate and 3vgate pins are each connected to a constant current source of 25 a, nominal. both the 5v and 3.3v outputs act as source followers, where: v source = [v gate v th(on) ] until the associated output is equal to its input. the voltages on the gates of the external mosfets for the 5v and 3.3v main supplies will continue to rise to approximately 11.5v, ensuring minimum r ds(on) of the mosfet. note that a delay exists between the on command to a slot and the appearance of voltage at the slot s 3.3v or 5v main output. this delay is the time required to charge the 3v or 5v gate output up to the threshold voltage of the external mosfet (typically about 4v). for the 5v and 3.3v main supplies, the source (output) side of the external mosfet will reach the drain (input) voltage in a time given by: t cv i delay gate drain gate source = ( ) ()
mic2593 micrel m9999-042204 12 april 2004 (decade-scale) standard capacitors. i gate(source) = 25 a c gate dv/dt (gate) 0.001 f 25v/ms 0.01 f 2.5v/ms 0.1 f 0.25v/ms 1 f 0.025v/ms table 1. 3.3v/5v gate output slew rate selection for the +12v and 12v supplies, the output slew rate is controlled by capacitors connected to the 12vslewa and 12vslewb pins. to determine the minimum value of the slew rate capacitor, (c slew ), and to ensure the device does not enter into current limit during start-up, the following equation is used: c min i i c slew slew lim 12v 12mv load () [/ ] = where c load is the load capacitance connected to the +12v and 12v outputs, i lim[12v/12mv] are the current limit slow-trip thresholds and i slew is the slew rate charge current found in the electrical characteristics table. the slew rate dv/dt is computed by: dv dt at load i c10 slew slew 6 / ( ) = by appropriately selecting the value of c slew , the magnitude of the inrush current will not exceed the current limit for a given load capacitance. since one capacitor fixes the slew rate for both +12v and 12v, the capacitor value should be chosen to provide the slower slew rate of the two. table 2 depicts the 12v output slew rate for various values of c slew . i slew = 22 a c gate dv/dt (load) 0.001 f 22v/ms 0.01 f 2.2v/ms 0.1 f 0.22v/ms 1 f 0.022v/ms table 2. 12v output slew rate selection power down cycle when a slot is turned off, internal switches are connected to each of the outputs to discharge the pci board's bypass capacitors to ground. standby mode standby mode is entered when any (one or more) enabled main supply input (12v in , 12mv in , 5v in and/or 3v in ) drops below its respective uvlo threshold. the mic2593 supplies two 3.3v auxiliary outputs, vaux[a/b], satisfying pci 2.x specifications. these outputs are fed via the vstby[a/b] input and controlled by the auxen[a/b] inputs or via their smi bus control registers. these outputs are independent of the main outputs: should one or more of the main supply inputs move below its uvlo thresholds, vaux[a/b] will still function as long as vstby[a/b] is present. prior to entering standby mode, ona and onb (or the maina and mainb bits in the control registers) inputs should be de-asserted. if this is not done, the mic2593 will assert /fault and also /int if interrupts are enabled, when the mic2593 detects an under- voltage condition on a supply input. circuit breaker functions the mic2593 provides an electronic circuit breaker function that protects against excessive loads, such as short circuits, at each supply. when the current from one or more of a slot s main outputs exceeds the current limit threshold (50mv/r sense for 3.3v and 5v, 1.0a for +12v, and/or 0.2a for 12v) for a duration greater than the overcurrent timer, t flt , the circuit breaker is tripped and all main supplies (all outputs except vaux[a/b]) are shut off. should the load current exceed i thfast (+12v and 12v), or cause a main output s v sense to exceed v thfast (+3.3v and +5v), the outputs are shut off with no delay. undervoltage conditions on the main supply inputs also trip the circuit breaker, but only when the main outputs are enabled (to signal a supply input brown-out condition). the vaux[a/b] outputs have their own separate circuit breaker functions. vaux[a/b] do not incorporate a fast-trip threshold, but instead regulate the output current into a fault to avoid exceeding their operating current limit. the circuit breaker will trip due to overcurrents on vaux[a/b] when the overcurrent fault timer (t flt ) expires. this use of the overcurrent timer prevents the circuit breaker from tripping prematurely due to brief current transients. following a fault condition, the outputs can be turned on again via the on inputs (if the fault occurred on one of the main outputs), via the auxen inputs (if the fault occurred on the aux outputs), or by cycling both on and auxen (if faults occurred on both the main and aux outputs). a fault condi- tion can alternatively be cleared under smi control of the enable bits in the cntrl[a/b] registers (see register bits d[1:0]). when the circuit breaker trips, /fault[a/b] will be asserted if the outputs were enabled through the hot plug interface inputs. at the same time, /int will be asserted (unless interrupts are masked). note that /int is de-asserted by writing a logic 1 back into the respective fault bit position(s) in the stat[a/b] register or the common status register. the response time (t flt ) of the mic2593 s primary overcur- rent detector is set by external capacitors at the cfilter[a/b] pins to gnd. for slot a, cfilter[a] is located at pin 2; for
april 2004 13 m9999-042204 mic2593 micrel main[a/b]pg (3) 3vaux_uv[a/b] (1) 12vout_uv[a/b] (1) 3vout_uv[a/b] (1) aux[a/b]pg (2) v stby[a/b] v stby[a/b] notes: 1. internal flag 2. cntrl[a/b] register bit d[7] 3. cntrl[a/b] register bit d[6] figure 7. power-good status logic diagram slot b, cfilter[b] is located at pin 35. for a given response time, the value for cfilter[a/b] is given by: cfilter a b f tmsia vv10 flt a b filter filter 3 [ / ]( ) () () () [/] = where t flt[a/b] is the selected overcurrent response time and i filter and v filter are specified in the electrical characteristics table. thermal shutdown the internal +12v, 12v, and v aux mosfets are protected against damage not only by current limiting, but by dual-mode overtemperature protection as well. each slot controller on the mic2593 is thermally isolated from the other. should an overcurrent condition raise the junction temperature of one slot s controller and internal pass elements to 140 c, all of the outputs for that slot (including v aux ) will be shut off, and the slot s /fault output will be asserted. the other slot s opera- tion will remain unaffected. however, should the mic2593 s overall die temperature exceed 160 c, both slots (all outputs, including v auxa and v auxb ) will be shut off, whether or not a current limit condition exists. a 160 c overtemperature con- dition additionally sets the overtemperature bit (ot_int) in the common status register. output power-good status for the mic2593, power-is-good is valid on a slot when the outputs of the four main supplies (12v, 12v, 5v, and 3.3v) and the auxiliary supply output are all above their respective power-good thresholds specified in the electrical character- istics table. the power-good status of either slot is verified by polling the cntrl[a/b] register bits d[7:6]. cntrl[a/b] register bits d[7] and d[6] indicate output power-good status for the aux supply and main supplies, respectively. figure 7 below illustrates an equivalent logic circuit that determines the output power-good status for the main and aux supplies. general purpose input (gpi) pins two pins on the mic2593 are available for use as gpi pins. the logic state of each of these pins can be determined by polling bits [4:5] of common status register. both of these inputs are compliant to 3.3v. if unused, connect the gpi[a/b] pins to gnd. fault reporting and /int interrupt generation smi-only control applications in applications where the mic2593 is controlled only by the smi, the on[a/b] and auxen[a/b] should be connected to gnd as shown in figure 6. in this case, the mic2593 s /fault[a/b] outputs and stat[a/b] register bit d[7] (fault[a/b]) are not activated, as fault status is determined by polling stat[a/b] register bits d[4:0] and cs (common status) register bits d[2:1]. individual fault bits in stat[a/b] and cs are asserted after power-on-reset when: either or both cntrl[a/b] register bits d[1:0] are asserted, and 12vin[a/b], 12mvin[a/b], 5vin[a/b], 3vin[a/b], or vstby[a/b] input voltage is lower than its respective ulvo threshold, or the fast oc circuit breaker[a/b] has tripped, or the slow oc circuit breaker[a/b] has tripped and its filter timeout has expired, or the slow oc circuit breaker[a/b] has tripped and slot[a/b] die temperature exceeds 140 c, or the mic2593 s global die temperature exceeds 160 c to clear any one or all stat[a/b] register bits d[4:0] and/or cs register bits d[2:1] once asserted, a software subroutine can perform an echo reset where a logical 1 is written back to those register bit locations that have indicated a fault. the open-drain, active-low /int output signal is activated after power-on-reset when the intmsk bit (cs register bit d[3]) has been reset to logical 0 . once activated, the /int output is asserted by any one of the fault conditions listed above and de-asserted when one or all stat[a/b] register bits d[4:0] and/or cs register bits d[2:1] are reset upon the execution of an smbus echo reset write_byte cycle.
mic2593 micrel m9999-042204 14 april 2004 /int* /fault_[a/b] i main_out[a/b] main_out[a/b] i aux_out[a/b] aux_out[a/b] auxen[a/b] 0 v ih v ih v il v ih i lim(aux) i steady-state i lim(main) i steady-state on[a/b] 0 0 0 0 0 0 0 v ih v il +3.3v t por vstby uvlo t flt t flt ** * /int de-asserted by software figure 8. hot plug interface operation hpi-only control applications in applications where the mic2593 is controlled only by the hpi, smbus signals scl, sda, and /int signals are con- nected to vstby as shown in figure 6. in this configuration, the mic2593 s /fault[a/b] outputs are activated after power- on-reset and become asserted when: either or both external on[a/b] and auxen[a/b] input sig- nals are asserted, and 12vin[a/b], 12mvin[a/b], 5vin[a/b], 3vin[a/b], or vstby[a/b] input voltage is lower than its respective ulvo threshold, or the fast oc circuit breaker[a/b] has tripped, or the slow oc circuit breaker[a/b] has tripped and its filter timeout[a/b] has expired, or the slow oc circuit breaker[a/b] has tripped and slot[a/b] die temperature exceeds 140 c, or the mic2593 s global die temperature exceeds 160 c in order to clear /fault[a/b] outputs once asserted, on[a/b] and/or auxen[a/b] input signals must be de-asserted. please see the /fault[a/b] pin description for additional informa- tion. hot plug interface (hpi) operation once the input supplies are above their respective uvlo thresholds, the hot plug interface can be utilized for power control by enabling the control input pins (auxen[a/b] and on[a/b]) for each slot. in order for the mic2593 to switch on the vaux supply for either slot, the auxen[a/b] control must be enabled after the power-on-reset delay, t por (typically 500 s), has elapsed. the main output supplies can also be enabled after t por . the timing response diagram of figure 8 illustrates a hot plug interface operation where an overcur- rent fault is detected by the mic2593 controller after initiating a power-up sequence. the figure illustrates the output re- sponse of /fault, /int, vaux[a/b] supplies, and an exter- nal mosfet control main[a/b] output supply, either 3.3v or 5v. mic2593 smbus address configuration the mic2593 responds to its own unique address which is assigned using a2, a1, and a0. these represent the 3 lsbs of its 7-bit address, as shown in table 3. these address bits are assigned only during power up of the vstby[a/b] supply input. these three bits allow up to eight mic2593 devices in a single system. these pins are either grounded or left unconnected to specify a logical 0 or 1, respectively. a pin designated as a logical 1 may also be pulled up to v stby . serial port operation the mic2593 uses standard smbus write_byte and read_byte operations for communication with its host. the smbus write_byte operation involves sending the device s slave address, with the r/w bit (lsb) set to the low (write) state, followed by a command byte and a data byte. the smbus read_byte operation is similar, but is a composite write and read operation: the host first sends the device s slave address followed by the command byte, as in a write operation. a new start bit must then be sent to the mic2593, followed by a repeat of the slave address with the r/w bit set to the high (read) state. the data to be read from the part may then be clocked out. there is one exception to this rule: if the location latched in the pointer register from the last write operation is known to be correct (i.e., points to the desired register within the mic2593), then the receive_byte proce-
april 2004 15 m9999-042204 mic2593 micrel mic2593 register set and programmer s model target register command byte value power-on default label description read write reserved do not use 00 h n/a n/a reserved do not use 01 h n/a n/a cntrla control register slot a 02 h 02 h 00 h cntrlb control register slot b 03 h 03 h 00 h stata slot a status 04 h 04 h 00 h statb slot b status 05 h 05 h 00 h cs common status register 06 h 06 h xxxx 0000 b reserved reserved / do not use 07 h - ff h 07 h - ff h undefined table 4. mic2593 register addresses s1001 a2 a1 a0 0a000000xxa d4 d5 d6 d3 d2 d1 d0 d7 ap mic2593 slave address data clk command byte to mic2593 data byte to mic2593 start stop r/w = write acknowledge acknowledge acknowledge master to slave transfer, i.e., data driven by master. slave to master transfer, i.e., data driven by slave. figure 9. write_byte protocol s1001a2a1a0 a2a1a0 0a000000 xxas1 1 1 00 d4 d5 d6 d3 d2 d1 d0 a d7 /a p mic2593 slave address data clk command byte to mic2593 mic2593 slave address data read from mic2593 start start stop r/w = write r/w = read acknowledge acknowledge acknowledge not acknowledge master to slave transfer, i.e., data driven by master. slave to master transfer, i.e., data driven by slave. figure 10. read_byte protocol s1001 a2 a1 a0 1a d4 d5 d6 d3 d2 d1 d0 d7 /a p mic2593 slave address data clk byte read from mic2593 start stop r/w = read acknowledge not acknowledge master to slave transfer, i.e., data driven by master. slave to master transfer, i.e., data driven by slave. figure 11. receive_byte protocol inputs mic2593 slave address a2 a1 a0 binary hex 0 0 0 1000 000 b 80 h 0 0 1 1000 001 b 82 h 0 1 0 1000 010 b 84 h 0 1 1 1000 011 b 86 h 1 0 0 1000 100 b 88 h 1 0 1 1000 101 b 8a h 1 1 0 1000 110 b 8c h 1 1 1 1000 111 b 8e h table 3. mic2593 smbus addressing dure may be used. to perform a receive_byte operation, the host sends an address byte to select the slave mic2593, with the r/w bit set to the high (read) state, and then retrieves the data byte. figures 9 through 11 show the formats for these data read and data write procedures. the command register is eight bits (one byte) wide. this byte carries the address of the mic2593 s register to be operated upon. the command byte values corresponding to the various mic2593 register addresses are shown in table 4. command byte values other than 0000 0xxx b = 00 h - 07 h are reserved and should not be used.
mic2593 micrel m9999-042204 16 april 2004 detailed register descriptions control register, slot a (cntrla) 8-bits, read/write control register, slot a (cntrla) d[7] d[6] d[5] d[4] d[3] d[2] d[1] d[0] read-only read-only read only read only read-only read only read/write read/write auxapg mainapg reserved reserved reserved reserved maina vauxa bit(s) function operation auxapg aux output power-good status, slot a 1 = power-is-good (vauxa output is above its uvlo threshold) mainapg main output power-good status, slot a 1 = power-is-good (maina outputs are above their uvlo thresholds) d[5] reserved always read as zero d[4] reserved always read as zero d[3] reserved always read as zero d[2] reserved always read as zero maina main enable control, slot a 0 = off, 1 = on vauxa vaux enable control, slot a 0 = off, 1 = on power-up default value: 0000 0000 b = 00 h read command_byte value (r/w): 0000 0010 b = 02 h the power-up default value is 00 h . slot is disabled upon power-up, i.e., all supply outputs are off.
april 2004 17 m9999-042204 mic2593 micrel control register, slot b (cntrlb) 8-bits, read/write control register, slot b (cntrlb) d[7] d[6] d[5] d[4] d[3] d[2] d[1] d[0] read-only read-only read only read only read-only read-only read/write read/write auxbpg mainbpg reserved reserved reserved reserved mainb vauxb bit(s) function operation auxbpg aux output power-good status, slot b 1 = power-is-good (vauxb output is above its uvlo threshold) mainbpg main output power-good status, slot b 1 = power-is-good (mainb outputs are above their uvlo thresholds) d[5] reserved always read as zero d[4] reserved always read as zero d[3] reserved always read as zero d[3] reserved always read as zero mainb main enable control, slot b 0 = off, 1 = on vauxb vaux enable control, slot b 0 = off, 1 = on power-up default value: 0000 0000 b = 00 h command_byte value (r/w): 0000 0011 b = 03 h the power-up default value is 00 h . slot is disabled upon power-up, i.e., all supply outputs are off.
mic2593 micrel m9999-042204 18 april 2004 status register slot a (stata) 8-bits, read-only status register, slot a (stata) d[7] d[6] d[5] d[4] d[3] d[2] d[1] d[0] read-only read-only read-only read/write read/write read/write read/write read/write faulta maina vauxa vauxaf 12mvaf 12vaf 5vaf 3vaf bit(s) function operation faulta fault status slot a 1 = /faulta pin asserted (/faulta pin is low) 0 = /faulta pin de-asserted (/faulta pin is high) see notes 1 and 2 maina main enable status slot a represents the actual state (on/off) of the four main power outputs for slot a (+12v, 12v, +5v and +3.3v) 1 = main power on 0 = main power off vauxa vaux enable status slot a represents the actual state (on/off) of the auxiliary power output for slot a 1 = aux power on 0 = aux power off vauxaf overcurrent fault: vauxa supply a 1 = fault 0 = no fault 12mvaf overcurrent fault: 12v supply a 1 = fault 0 = no fault 12vaf overcurrent fault: +12v supply a 1 = fault 0 = no fault 5vaf overcurrent fault: 5v supply a 1 = fault 0 = no fault 3vaf overcurrent fault: 3.3v supply a 1 = fault 0 = no fault power-up default value: 0000 0000 b = 00 h command_byte value (r/w): 0000 0100 b = 04 h the power-up default value is 00 h . both slots are disabled upon power-up, i.e., all supply outputs are off. in response to an overcurrent fault condition, writing a logical 1 back into the active (or set) bit position will clear the bit and de-assert /i nt. the status of the /faulta pin is not affected by reading the status register or by clearing active status bits. notes: 1. if faulta has been set by an overcurrent condition on one or more of the main outputs, the ona input must go low to reset fa ulta. if faulta has been set by a vauxa overcurrent event, the auxena input must go low to reset faulta. if an overcurrent has occurred on both a main output and the vaux output of slot a, both ona and auxena of the slot must go low to reset faulta. 2. neither the faulta bit nor the /faulta pin is active when the mic2593 power paths are controlled by the system management int erface. when using smi power path control, auxena and ona pins for that slot must be tied to gnd.
april 2004 19 m9999-042204 mic2593 micrel status register slot b (statb) 8-bits, read-only status register, slot b (statb) d[7] d[6] d[5] d[4] d[3] d[2] d[1] d[0] read-only read-only read-only read/write read/write read/write read/write read/write faultb mainb vauxb vauxbf 12mvbf 12vbf 5vbf 3vbf bit(s) function operation faultb fault pin status slot b 1 = /faultb pin asserted (/faultb pin is low) 0 = /faultb pin de-asserted (/faultb pin is high) see notes 1 and 2 mainb main enable status slot b represents the actual state (on/off) of the four main power outputs for slot b (+12v, 12v, +5v and +3.3v) 1 = main power on 0 = main power off vauxb vaux enable status slot b represents the actual state (on/off) of the auxiliary power output for slot b 1 = aux power on 0 = aux power off vauxbf overcurrent fault: vauxb supply b 1 = fault 0 = no fault 12vmbf overcurrent fault: 12v supply b 1 = fault 0 = no fault 12vbf overcurrent fault: +12v supply b 1 = fault 0 = no fault 5vbf overcurrent fault: 5v supply b 1 = fault 0 = no fault 3vbf overcurrent fault: 3.3v supply b 1 = fault 0 = no fault power-up default value: 0000 0000 b = 00 h command_byte value (r/w): 0000 0101 b = 05 h the power-up default value is 00 h . both slots are disabled upon power-up, i.e., all supply outputs are off. in response to an overcurrent fault condition, writing a logical 1 back into the active (or set) bit position will clear the bit and de-assert /i nt. the status of the /faultb pin is not affected by reading the status register or by clearing active status bits. notes: 1. if faultb has been set by an overcurrent condition on one or more of the main outputs, the onb input must go low to reset fau ltb. if faultb has been set by a vauxb overcurrent event, the auxenb input must go low to reset faultb. if an overcurrent has occurred on both a main output and the vaux output of slot b, both onb and auxenb of the slot must go low to reset faultb. 2. neither the faultb bit nor the /faultb pin is active when the mic2593 power paths are controlled by the system management int erface. when using smi power path control, the auxenb and onb pins for that slot must be tied to gnd.
mic2593 micrel m9999-042204 20 april 2004 common status register (cs) 8-bits, read/write common status register (cs) d[7] d[6] d[5] d[4] d[3] d[2] d[1] d[0] read-write read-write read-only read-only read-write read-write read-write read-only reserved reserved gpi_b gpi_a intmsk uv_int ot_int reserved bit(s) function operation d[7] reserved always read as zero d[6] reserved always read as zero gpi_b general purpose input 0, slot b state of gpib pin gpi_a general purpose input 0, slot a state of gpia pin intmsk interrupt mask 0 = /int generation is enabled. 1 = /int generation is disabled. the mic2593 does not participate in the smbus alert response address (ara) protocol. uv_int undervoltage interrupt 0 = no uvlo fault 1 = uvlo fault set whenever a circuit breaker fault condition occurs as a result of an undervoltage lockout condition on one of the main supply inputs. this bit is only set if a uvlo condition occurs while the on[a/b] pin is asserted or the main[a/b] control bits are set. ot_int overtemperature interrupt 0 = die temp < 160 c. 1 = fault: die temp > 160 c. set if a fault occurs as a result of the mic2593 s die temperature exceeding 160 c. d[0] reserved undefined. power-up default value: 00000000 b = 00 h command_byte value (r/w): 00000110 b = 06 h to reset the ot_int and uv_int fault bits, a logical 1 must be written back to these bits.
april 2004 21 m9999-042204 mic2593 micrel application information current sensing for the three power supplies switched with internal mos- fets (+12v, 12v, and v aux ), the mic2593 provides all necessary current sensing functions to protect the ic, the load, and the power supply. for the remaining four supplies which the part is designed to control, the high currents at which these supplies typically operate make sensing the current inside the mic2593 impractical. therefore, each of these supplies, 3v[a/b] and 5v[a/b], requires an external current sensing resistor. the v in connection to the ic from each supply (e.g., 5vina) is connected to the positive termi- nal of the slot s current sense amplifier, and the correspond- ing sense input (in this case, 5vsensea) is connected to the negative terminal of the current sense amplifier. sense resistor selection the mic2593 uses low-value sense resistors to measure the current flowing through the mosfet switches to the loads. these sense resistors are nominally valued at 50mv/i load(cont) . to accommodate worst-case tolerances for the sense resistor (allow 3% over time and temperature for a resistor with 1% initial tolerance) and still supply the maximum required steady-state load current, a slightly more detailed calculation must be used. the current limit threshold voltage (i.e., the trip point ) for the mic2593 may be as low as 35mv, which would equate to a sense resistor value of 35mv/i load(cont) . carrying the numbers through for the case where the value of the sense resistor is 3% high yields this: r 35mv 103 i 34mv i sense load cont load cont = ( ) ( ) = . () () once the value of r sense has been chosen in this manner, it is good practice to check the maximum i load(cont) which the circuit may let through in the case of tolerance build-up in the opposite direction. here, the worst-case maximum cur- rent is found using a 65mv trip voltage and a sense resistor which is 3% low in value. the resulting current is: i 65mv (0.97)(r ) 67mv r load(cont, max) sense(nom) sense(nom) == as an example, if an output must carry a continuous 4.5a without nuisance trips occurring, r sense for that output should be 34m ? /4.5a = 7.55m ? . the nearest standard value is 7.5m ? , so a 7.5m ? 1% resistor would be a good choice. at the other set of tolerance extremes for the output in question, i load(cont,max) = 67mv/7.5m ? = 8.93a. knowing this final datum, we can determine the necessary wattage of the sense resistor, using p = i 2 r, where i is i load(cont, max) , and r is (0.97)(r sense(nom) ). these numbers yield the following: p max = (8.93a) 2 (7.28m ? ) = 0.581w a 1w sense resistor would work well in this application. kelvin sensing because of the low values of the sense resistors, special attention to the layout must be used in order for the mic2593's circuit breaker function to operate properly. specifically, the use of a 4-wire kelvin connection to measure the voltage across r sense is highly recommended. kelvin sensing is simply a means of making sure that any voltage drops in the power traces connecting to the resistors does not get picked up by the traces themselves. the kelvin connections should be isolated from all other signal traces to avoid introducing noise onto these sensitive nodes. additionally, a high-fre- quency noise filter across the sense inputs is highly recom- mended to avoid nuisance tripping of the (overcurrent) circuit breaker on the opposite slot to the slot that incurred an overcurrent event. due to the variation of each system's susceptibility to noise, the exact value of this filter is experi- mentally determined. a value between 10pf to 100pf is a good starting point. figure 12 illustrates how kelvin sensing is performed. all the high current in the circuit (from the 5v supply through r sense and then to the drain of the 5v (slot a) output mosfet) flows directly through the power pcb traces and r sense . the voltage drop resulting across r sense is sampled in such a way that the high currents through the power traces will not introduce any extraneous ir drops. r sense power trace from 5v in power trace to mosfet drain signal trace to mic2593 v in signal trace to mic2593 v sense 5vina 5vsensea mic2593 22pf figure 12. kelvin sense connections for r sense (applicable to 5v[a/b] and 3v[a/b]) mosfet selection selecting the proper mosfet for use as a current pass and switching element for each of the 3v and 5v slots of the mic2593 primarily involves three straightforward tasks: 1. choice of a mosfet which meets the minimum voltage requirements. 2. selection of a device to handle the maximum continuous current (steady-state thermal issues). 3. verification that the selected part can withstand any current peaks (transient thermal issues). mosfet voltage requirements the first voltage requirement for each mosfet is easily stated: the drain-source breakdown voltage of the mosfet
mic2593 micrel m9999-042204 22 april 2004 must be greater than v in(max) for the slot in question. for instance, the 5v input may reasonably be expected to see high-frequency transients as high as 6.5v. therefore, the drain-source breakdown voltage of the mosfet must be at least 7v. the second breakdown voltage criteria which must be met is a bit subtler than simple drain-source breakdown voltage, but is not hard to meet. low-voltage mosfets generally have low breakdown voltage ratings from gate to source as well. in mic2593 applications, the gates of the external mosfets are driven from the +12v input to the mic2593 controller. that supply may well be at 12v + (5% x 12v) = 12.6v. at the same time, if the output of the mosfet (its source) is suddenly shorted to ground, the gate-source voltage will go to (12.6v 0v) = 12.6v. this means that the external mosfets must be chosen to have a gate-source breakdown voltage in excess of 13v; after 12v absolute maximum, the next commonly available voltage class has a 20v maximum gate-source voltage. at the present time, most power mosfets with a 20v gate-source voltage rating have a 30v drain-source breakdown rating or higher. as a general tip, look to surface mount devices with a drain-source rating of 30v as a starting point. mosfet steady-state thermal issues the selection of a mosfet to meet the maximum continuous current is a fairly straightforward exercise. first, arm yourself with the following data: the value of i load(cont, max) for the output in question (see sense resistor selection ). the manufacturer s data sheet for the candidate mosfet. the maximum ambient temperature in which the device will be required to operate. any knowledge you can get about the heat sinking available to the device (e.g., can heat be dissi- pated into the ground plane or power plane if using a surface mount part? is any airflow available?). the data sheet will almost always give a value of on resis- tance given for the mosfet at a gate-source voltage of 4.5v, and another value at a gate-source voltage of 10v. as a first approximation, add the two values together and divide by two to get the on-resistance of the part with 7v to 8v of enhance- ment (11.5v nominal v gate minus the 3.5v to 4.5v gate threshold of the mosfet). call this value r on . since a heavily enhanced mosfet acts as an ohmic (resistive) device, almost all that s required to determine steady-state power dissipation is to calculate i 2 r. the one addendum to this is that mosfets have a slight increase in r on with increasing die temperature. a good approximation for this value is 0.5% increase in r on per c rise in junction tempera- ture above the point at which r on was initially specified by the manufacturer. for instance, if the selected mosfet has a calculated r on of 10m ? at t j = 25 c and the actual junction temperature ends up at 110 c, a good first cut at the operat- ing value for r on would be: r on ? 10m ? [1 + (110 25)(0.005)] ? 14.3m ? next, approximate the steady-state power dissipation (i 2 r) using i load(cont,max) and the approximated r on . p d ? [i load(cont, max) ] 2 r on ? (8.93a) 2 14.3m ? ? 1.14w the final step is to make sure that the heat sinking available to the mosfet is capable of dissipating at least as much power (rated in c/w) as that with which the mosfet s performance was specified by the manufacturer. here are a few practical tips: 1. the heat from a surface-mount device such as an so-8 mosfet flows almost entirely out of the drain leads. if the drain leads can be soldered down to one square inch or more, the copper trace will act as the heat sink for the part. this copper trace must be on the same layer of the board as the mosfet drain. 2. airflow works. even a few lfm (linear feet per minute) of air will cool a mosfet down substan- tially. if you can, position the mosfet(s) near the inlet of a power supply s fan, or the outlet of a processor s cooling fan. 3. the best test of a surface-mount mosfet for an application (assuming the above tips show it to be a likely fit) is an empirical one. check the mosfet's temperature in the actual layout of the expected final circuit, at full operating current. the use of a thermocouple on the drain leads, or infrared py- rometer on the package, will then give a reason- able idea of the device s junction temperature. mosfet transient thermal issues having chosen a mosfet that will, a) withstand both the applied voltage stresses, and b) handle the worst-case continu- ous i 2 r power dissipation that it will endure; verifying the mosfet s ability to handle short-term overload power dissipa- tion without overheating is the lone item to be determined. a mosfet can handle a much higher pulsed power without damage than its continuous dissipation ratings would imply. the reason for this is that thermal devices (silicon die, lead frames, etc.) have thermal inertia. in terms related directly to the specification and use of power mosfets, this is known as transient thermal impedance. almost all power mosfet data sheets give a transient thermal impedance curve. for example, take the case where t flt for the 5v supply has been set to 50ms, i load(cont, max) is 5.0a, the slow-trip threshold is 50mv nominal, and the fast-trip threshold is 100mv. if the output is connected to a 0.60 ? load, the output current from the mosfet for the slot in question will be regulated to 5.0a for
april 2004 23 m9999-042204 mic2593 micrel 50ms before the mic2593 circuit breaker trips. during that time, the dissipation in the mosfet is given by: p = e i; e mosfet = [5v 5a(0.6 ? )] = 2v p mosfet = (2v 5a) = 10w for 50ms at first glance, it would appear that a really hefty mosfet is required to withstand this sort of fault condition. this is where the transient thermal impedance curves become very useful. figure 13 shows the curve for the vishay (siliconix) si4430dy, a commonly used so-8 power mosfet. taking the simplest case first, we ll assume that once a fault event such as the one in question occurs, it will be a long time, several seconds, before the fault is isolated and the channel is reset. in such a case, we can approximate this as a single pulse event, that is to say, there s no significant duty cycle. then, reading up from the x-axis at the point where square wave pulse duration is equal to 0.1sec (=100msec), we see that the z (j-a) of this mosfet to a highly infrequent event of this duration is only 7% of its continuous r (j-a) . this particular part is specified as having an r (j-a) of 35 c/w for intervals of 10 seconds or less. thus: assume t a = 55 c maximum, 1 square inch of copper at the drain leads, no airflow. recalling from our previous approximation hint, the part has an r on of (0.014/2) = 7m ? at 25 c. assume it has been carrying just about 5a for some time. when performing this calculation, be sure to use the highest anticipated ambient temperature (t a(max) ) in which the mosfet will be operating as the starting temperature, and find the operating junction temperature increase ( ? t j ) from that point. then, as shown next, the final junction temperature is found by adding t a(max) and ? t j . since this is not a closed- form equation, getting a close approximation may take one or two iterations, but it s not a hard calculation to perform and tends to converge quickly. then the starting (steady-state)t j is: t j ? t a(max) + ? t j ? t a(max) + [r on + (t a(max) t a )(0.005/ c)(r on )] i 2 r (j-a) t j ? 55 c + [7m ? + (55 c 25 c)(0.005)(7m ? )] (5a) 2 (35 c/w) t j ? (55 c + (0.20125w)(35 c/w) ? 62.0 c iterate the calculation once to see if this value is within a few percent of the expected final value. for this iteration we will start with t j equal to the already calculated value of 62.0 c: t j ? t a + [7m ? + (62.0 c-25 c)(0.005)(7m ? )] (5a) 2 (35 c/w) t j ? ( 55 c + (0.21008w)(35 c/w) ? 62.35 c so our original approximation of 62.0 c was very close to the correct value. we will use t j = 62 c. finally, add (10w)(35 c/w)(0.07) = 24.5 c to the steady-state t j to get t j(transient max.) = 86.5 c. this is an acceptable maximum junction temperature for this part. 10 -4 10 -3 10 -2 10 -1 1 10 100 600 2 1 0.1 0.01 0.2 0.1 0.05 0.02 single pulse duty cycle = 0.5 normalized thermal transient imperance, juction-to-ambient 1. duty cycle, d = 2. per unit base = r ja = 67 c/w 3. t jm t a = p dm z ja (t) 4. surface mounted t 1 t 2 t 1 t 2 notes: p dm square wave pulse duration (sec) normalized effective transient thermal impedance figure 13. si4430dy mosfet transient thermal impedance curve
mic2593 micrel m9999-042204 24 april 2004 mosfet vendors key mosfet type(s) web address vishay (siliconix) si4430dy ( little foot series) www.siliconix.com si4420dy ( little foot series) international rectifier irf7413a (so-8 package part) www.irf.com si4420dy (second source to vishay) fairchild semiconductor fds6644 (so-8 package part) www.fairchildsemi.com fds6670a (so-8 package part) fds6688 (so-8 package part) resistor vendors sense resistors web address vishay (dale) wsl series wsl 3637 series www.vishay.com/docs/wsl_30100.pdf irc oars series irctt.com/pdf_files/oars.pdf lr series irctt.com/pdf_files/lrc.pdf (second source to wsl) table 5. power mosfet and resistor values mosfet and sense resistor selection guide listed in table 5 below, by manufacturer and type number, are some of the more popular mosfet and resistor types used in pci hot plug applications. although far from compre- hensive, this information will constitute a good starting point for most designs. power supply decoupling in general, prudent system design requires that power sup- plies used for logic functions should have less than 100mv of noise at frequencies of 100khz and above. in particular, the 12v supply should have less than 100mv of peak-to-peak noise at frequencies of 1mhz or higher. this is because the 12v supply is the most negative potential applied to the ic, and is therefore connected to the device's substrate. all of the subcircuits integrated onto the silicon chip are hence sub- jected by capacitive coupling to any hf noise on the 12v supply. while individual capacitances are quite low, the amount of injected energy required to cause a "glitch" can also be quite low at the internal nodes of high speed logic circuits. less obviously, but equally important, is the fact that the internal charge pump for the 3.3v aux supplies is somewhat susceptible to noise on the +12v input when that input is at or near zero volts. the +12v supply should not carry hf noise in excess of 200mv peak-to-peak with respect to chip ground when it is in the "off" state. if either the 12v input, the +12v input, of both supplies do carry significant hf noise (as can happen when they are locally derived by a switching converter), the solution is both small and inexpensive. an lc filter made of a ferrite bead between the noisy power supply input and the mic2593, followed by a "composite capacitor" from the affected mic2593 input pin to ground, will suffice for almost any situation. a good composite capacitor for this purpose is the parallel combination of a 47 f tantalum bulk decoupling capacitor, and one 1 f and one 0.01 f ceramic capacitor for high- frequency bypass. a suggested ferrite bead for such use is fair-rite products corporation part number 2743019447 (this is a surface-mountable part). similar parts from other vendors or a 0.27 h air-core coil can also be used. noisy v in to mic2593 smt ferrite bead fair-rite products type 2743019447 47 f tanalum 1 f ceramic 10nf ceramic figure 14. filter circuit for noisy supplies (+3.3v and/or 12v) it is theoretically possible that high-amplitude, hf noise reflected back into one or both of the mic2593 s 12v outputs could interfere with proper device operation, although such noisy loads are unlikely to occur in the real world. if this becomes an application-specific concern, a pair of filters similar to that in figure 14 will provide the required hf bypassing. the capacitors would be connected to the mic2593 s 12v output pins, and the ferrite beads would be placed between the 12v output pins and the loads. 12v input clamp diode the 12v input to the mic2593 is the most negative potential on the part and is therefore connected to the chip s substrate (as described in power supply decoupling, above). al- though no particular sequencing of the 12v supply relative to the other mic2593 supplies is required for normal opera- tion, this substrate connection does mean that the 12v input must never exceed the voltage on the ground pin of the ic by more than 0.3 volts. small amounts of internal leakage current can cause this to happen when the vstby pins are energized and the 12mvin pins are not energized. in addition, power supply output ringing or l(di/dt) effects in the wiring and on the pcb itself will cause brief transient voltages in excess of +0.3v to appear at the 12v input. for this reason, it is required to clamp the 12v input to ground with a schottky diode. a diode rated at 1 amp and 20v to 40v as shown in our application schematic diagram is suggested. the diode s anode should be physically placed directly at the 12v input to the mic2593, and its cathode should have as short a path as possible back to the part s ground. a good smt part for this application is a type mbrs140t3 (1a, 40v).
april 2004 25 m9999-042204 mic2593 micrel gate capacitor and resistor guidelines the mic2593 controls four external power mosfets, that handle the high currents for each of the two 3.3v and 5v outputs. a capacitor is connected in the application circuit from each gate pin of the mic2593 to ground. however, an external capacitor, c gate , is not required for operation of the mic2593. each c gate controls the ramp-up rate of its respective power output (e.g., 5voutb). these capacitors, which are typically in the 10nf range, cause the gate outputs of the mic2593 to have very low ac impedances to ground at any significant frequency. it is therefore necessary to place a modest value of gate damping resistance (r gate ) between each c gate and the gate of its associated mosfet as shown in figure 15. these resistances prevent high- frequency mosfet source-follower oscillations from occur- ring. the exact value of the resistors used is not critical; 10 ? to 33 ? is usually a sufficient choice. each r gate should be physically located directly adjacent to the mosfet gate lead to which it connects. mic2593 gate r gate 15 ? c gate 10nf external mosfet figure 15. c gate and r gate connection
mic2593 micrel m9999-042204 26 april 2004 package information micrel, inc. 1849 fortune drive san jose, ca 95131 usa tel + 1 (408) 944-0800 fax + 1 (408) 474-1000 web http://www.micrel.com the information furnished by micrel in this data sheet is believed to be accurate and reliable. however, no responsibility is a ssumed by micrel for its use. micrel reserves the right to change circuitry and specifications at any time without notification to the customer. micrel products are not designed or authorized for use as components in life support appliances, devices or systems where malfu nction of a product can reasonably be expected to result in personal injury. life support devices or systems are devices or systems that (a) are intend ed for surgical implant into the body or (b) support or sustain life, and whose failure to perform can be reasonably expected to result in a significant inj ury to the user. a purchaser s use or sale of micrel products for use in life support appliances, devices or systems is at purchaser s own risk and purchaser agrees to fully indemnify micrel for any damages resulting from such use or sale. ? 2004 micrel, incorporated.

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