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mic2342/2342r dual-slot pci express ? hot-plug controller june 2008 1 m9999-062008-a general description the mic2342 is a dual-slot power controller supporting the power distribution requirement s for peripheral component interconnect express (pci express ? ) hot-plug compliant systems. the mic2342 provi des complete power control support for two pci express slots, including the 3.3vaux defined by the pci express st andards. support for the 12v, 3.3v, and 3.3vaux supplies includes programmable gate voltage slew-rate cont rol, voltage supervision, programmable current limit, and circuit breaker functions. these features provide compr ehensive system protection and fault isolation. additi onally, in the event of an overcurrent fault on 3.3vaux that ?trips? the circuit breaker to cause the 3.3vaux output to shut down, the main outputs (3.3v and 12v) for the affected 3.3vaux slot, a or b, will also be shut down . the mic234 1 controller provides truly independent out put operation for main and aux. data sheets and support doc umentation can be found on micrel?s web site at: www.micrel.com. features ? supports two independent pci express slots ? main & aux outputs are inter-dependent during aux overcurrent conditions ? 12v, 3.3v, and 3.3vaux supplies supported per pci express specification v1.0a, v.2.0 ? integrated power mosf ets for 3.3vaux rails ? standby operation for wake-on-lan applications with low backfeed on main +12v and +3.3v rails ? electronic circuit breakers for each supply per slot - programmable gate voltage slew-rate control - active current regulation controls inrush current ? high accuracy primary and secondary circuit breaker current-limit thresholds ? dual-level, dual-speed fault detection for fast response without nuisance tripping ? user-programmable primar y overcurrent detector ? /pwrgd and delayed /pwrgd (164 ms) signal outputs per slot ? separate /fault output signals for main and aux rails for each slot ? global systems power-is-good output ? both slots thermally isolated ? internally debounced plug-in card retention switch inputs per slot. applications ? pci express v1.0a, v2.0 hot-plug power control
micrel, inc. mic2342/2342r june 2008 2 m9999-062008-b ordering information part number latch off auto-retry 12v and 3v fast-trip thresholds 3.3vaux nominal current limit package mic2342?2ytq mic2342r?2ytq 100mv 0.375a 48 pin tqfp mic2342?3ytq (1) mic2342r?3ytq (1) 150mv 0.375a 48 pin tqfp mic2342?5ytq (1) mic2342r?5ytq (1) disabled 0.375a 48 pin tqfp note: 1. contact factory for availability
micrel, inc. mic2342/2342r june 2008 3 m9999-062008-b typical application
micrel, inc. mic2342/2342r june 2008 4 m9999-062008-b pin configuration
micrel, inc. mic2342/2342r june 2008 5 m9999-062008-b pin description pin number pin name pin function 5 32 12vina 12vinb 12v supply power and sense inputs [a/b]: two pins are provided for kelvin connection (one for each slot). pin 5 is the (+) kelvin-sense connection to the supply side of the sense resistor for 12v slot a. pin 32 is the (+) kelvin-sense connection to the supply side of the s ense resistor for 12v slot b. these two pins must ultimately connect to each other as close as possible at the mic2342 controller in order to eliminate any ir drop between these pins. an undervoltage lockout circuit (uvlo) prevents the swit ches from turning on while this input is lower than its lockout threshold voltage. 12 25 3vina 3vinb 3.3v supply power and sense inputs [a/b]: two pins are provided for connection (one for each slot). pin 12 is the (+) kelvin-sense connection to the supply side of the sense resistor for 3v slot a. pin 25 is the (+) kelvin-sense connection to the supply side of the sens e resistor for 3v slot b. these two pins must ultimately connect to each other as close as possible at the mic2342 controller in order to eliminate any ir drop between these pins. an undervoltage lockout circuit (uvlo) prevents the swit ches from turning on while this input is lower than its lockout threshold voltage. 16 21 3vouta 3voutb 3.3v power-good sense inputs: connect to 3.3v[a/b] outputs. used to monitor the 3.3v output voltages for 3. 3v output power-is-good status. 10 27 12vouta 12voutb 12v power-good sense inputs: connect to 12v[a/b] outputs. used to monitor the 12v output voltages for 12 v output power-is-good status. 8 29 12vsensea 12vsenseb 12v circuit breaker sense input [a/b]: the current limit thresholds are set by connecting sense resistors between these pins and 12vin[a/b]. when the 12v primary overcurrent detecto r current-limit threshold of 50mv is reached, the 12vgate[a/b] pin is modulated to maintain a constant voltage across the sense resistor and therefore a co nstant current into the load. if the 50mv threshold is exceeded for t flt or t dflt (whichever is shorter), the circuit breaker is tripped and the corresponding 12vgate pin for the affected slot is immediately pulled up to its corresponding 12vin to tu rn off the external mosfet. 13 24 3vsensea 3vsenseb 3v circuit breaker sense input [a/b]: the current limit thresholds are set by connecting sense resistors between these pins and 3vin[a/b]. when the 3v primary overcurrent detecto r current-limit threshold of 50mv is reached, the 3vgate[a/b] pin is modulated to maintain a constant voltage across the sense resistor and therefore a co nstant current into the load. if the 50mv threshold is exceeded for t flt or t dflt (whichever is shorter), the circuit breaker is tripped and the corresponding 3vgate pin for the affe cted slot is immediately pulled down to agnd to turn off the external mosfet. 3 24 12vgatea 12vgateb 12v gate drive outputs [a/b]: each pin connects to the gate of an external p- channel power mosfet. during power-up, the external c gate (if used) and the c gs of the external mosfets are connected to a 25a current sink. this controls the value of dv/dt seen at the source of the mosfets, and hence the current flowing into the 12v load capacitance. during current limit events, the voltage at this pin is adjusted to maintain constant current through the fet for a period of t flt or t dflt (whichever is shorter). whenever an overcurrent, ther mal shutdown, or input undervoltage fault condition occurs, the correspondi ng 12vgate pin for the affected slot is pulled up to its corresponding 12vin pi n to turn off the external mosfet.
micrel, inc. mic2342/2342r june 2008 6 m9999-062008-b pin description (cont.) pin number pin name pin function 14 23 3vgatea 3vgateb 3v gate drive outputs [a/b]: each pin connects to the gate of an external n - ch annel power mosfet. during power-up, the c gate (if used) and the c gs of the external mosfets are connected to a 25a current source. this controls the value of dv/dt seen at the source of the mosfets, and hence the current flowing into the 3v load capacitance. during current limit events, the voltage at this pin is adjusted to maintain constant current through the fet for a period of t flt or t dflt (whichever is shorter). whenever an overcurrent, ther mal shutdown, or input undervoltage fault condition occurs, the correspondi ng 3vgate pin for the affected slot is pulled down to agnd to turn off the external mosfet. 11 26 vstbya vstbyb 3.3v standby supply voltage: required to support the pci express vaux output. additionally, all internal logic circuitry operates on vstby[a/b]. an internal uvlo circuit prevents turn-on of the external 3.3vaux supply until the voltage at the vstby[a/b] pi ns is higher than the v uvlo(stby) threshold voltage. both pins must be externally connect ed together at the mic2342 controller. 15 22 vauxa vauxb 3.3vaux[a/b] outputs to pci express ca rd slots: these outputs connect the 3.3aux pin of the pci express connecto rs to vstby[a/b] via internal 0.4- ? mosfets. these outputs are current li mited and protected against short-circuit faults. 44 43 ona onb main +12vout[a/b] and +3.3vout[a/b] enable inputs: thes e level-sensitive digital inputs are each internally connec ted with pull-up resistors to vstby[a] and are used to enable or disable the main[a/b] (+3.3v and +12v) outputs. applying a high-to-low transition on on[a/b] for at least 200ns (t lpw ) after a fault resets the +12v and/or +3.3v fault latc hes for the affected slot and de-asserts the /fault_main[a/b] output signals. t he +12v and/or the +3.3v electronic circuit breakers are reset once the /f ault_main[a/b] output signals are de- asserted. 45 42 auxena auxenb vaux[a/b] enable inputs: these level-sensit ive digital inputs are each internally connected with pull-up resistors to vstby[a] and are used to enable or disable the vaux[a/b] outputs. appl ying a high-to-low transition on auxen[a/b] for at least 200ns (t lpw ) after a fault resets the vaux fa ult latches for the affected slot and de-asserts the /fault_aux[a/b] out put signals. the vaux[a/b] electronic circuit breakers are reset once the /f ault_aux[a/b] output signals are de- asserted. 2 35 cfiltera cfilterb overcurrent filter capacitor [a/b]: capacitors connected between these pins and agnd set the duration of t flt , the response time of the primary overcurrent (oc) detector circuits. t flt is the amount of time for which a slot remains in current limit before its circuit breaker is tripped. to configure the controller to use its internal digital filter delay timer, cfilter[a/b] pins shall be connected to agnd. if the overcurrent filter time s out during an aux fault condition to shutdown the aux output, the main output s of the corresponding slot will also be shutdown (see the ?output signals? ti ming responses? in figure 9 in the functional description section). 6 31 /pwrgda /pwrgdb /pwrgd[a/b] are open-drain, asserted active-low digital outputs that are normally connected by an external 10k ? pull-up resistor (each) to vstby. each output signal is asserted when inputs signals on[a/b] and auxen[a/b] have been enabled, each output voltage has crossed its respective power-is-good output threshold (v uvth(12v) , v uvth(3v) , and v uvth(vaux) threshold voltages), and no fault conditions exist . please consult the /pwrgd[a/b] and the /dly_pwrgd[a/b] state diagrams in the ap plications information section for more detail.
micrel, inc. mic2342/2342r june 2008 7 m9999-062008-b pin description (cont.) pin number pin name pin function 1 36 /fault_maina /fault_mainb /fault_main[a/b] outputs are open-drain, asserted active-low digital outputs that are normally connected by an external 10k ? resistor to vstby. asserted whenever the primary or secondary circuit breaker trips because of an overcurrent fault condition or an input undervoltage. applying a high-to-low transition at the on[a/b] pin resets the /fault_main[a/ b] outputs if /fault_main[a/b] was asserted in response to a fault condition on one of the slot?s main outputs (+12v or +3.3v). if an overcurrent event asserted /f ault_main[a/b], the respective output?s circuit breaker is reset when /fault_main[a/b] output signal is de-a sserted. a 200ns minimum pulse width (t lpw ) for on[a/b] will reset the main outputs in the event of an overcurrent fault once the fault is removed. if a fault condition occurred on both the main and vaux outputs of the same slot, then a high-to-low transition on both on[a/b] and auxen[a/b] must be applied to de-assert the /fault_main[a/b] and /fault_aux[a/b] outputs. to simplify system fault reporting, t he /fault_main[a/b] output pins may be connected together with t he /fault_aux[a/b] output pins. 4 39 /crswa /crswb card retention switch inputs [a/b]. these are level sensitive, asserted active- low digital inputs with internal pull-up resistors to vstby[a]. these inputs can be connected to the prnst#1 or prnst#2 pins on a pcie connector to indicate to the mic2342 that a pcie plug-in card is pr esent and firmly mated. internally, the mic2342?s +12vgate[a/b], +3vgate[a/b] , and 3vaux[a/b] gate drive circuits are gated with the mic2342?s on[a/b] and the auxen[a/b] inputs to deliver power to the connector only when a pcie plug-in ca rd is present. during operation, if the /crsw[a/b] inputs are disconnected or if there is a pc board trace failure, all outputs on the respective slot are turned off without delay. each of these inputs exhibit an internal switch debounce delay of approximately 10ms. 48 37 /fault_auxa /fault_auxb /fault_aux[a/b] outputs are open-drain, asserted active-low digital outputs that are normally connected by an external 10k ? resistor to vstby. asserted whenever the vaux[a/b] circuit breaker trips because of an overcurrent fault condition or a slot/die overtemperature condition. appl ying a high-to-low transition at the auxen[a/b] pin for at least 0.5s rese ts the /fault_aux[a/b] outputs if the /fault_aux[a/b] output signal was asserted in response to a fault condition on the respective slot?s vaux output. if an ov ercurrent event asserted /fault_aux[a/b], the respective output?s vaux circuit break er is reset when /fault_aux[a/b] output signal is de-asserted. a 200ns minimum pulse width (t lpw ) for aux_en[a/b] will reset the main outputs in the event of an overcurrent fault once the fault is removed. if a fault condition occurred on both the main and vaux outputs of the same slot, then a high-to-low transition on both on[a/b] and auxen[a/b] must be applied to de-assert the /fault_main[a/b] and /fault_aux[a/b] outputs. to simplify system fault reporting, the /fault_aux[a/b] output pins may be connected together with the /fault_main[a/b] output pins. 9 28 /force_ona /force_onb force on enable inputs [a/b]: these active-low, level-sensitive inputs with internal pull-up current ( a) to vstby[a] will turn on all thre e of the respective slot?s outputs (+12v, +3.3v, and vaux), while specifical ly defeating all protections on those supplies when asserted. this explicitly inc ludes all overcurrent and short circuit protections and on-chip thermal protecti on for the vaux[a/b] supplies. additionally included are the uvlo protections for the +3.3v and +12v main supplies. the /force_on[a/b] pins do not disable uvlo protection for the vaux[a/b] supplies. these input pins are intended for diagnostic purposes only. asserting /force_on[a/b] will cause the respective slot?s /pwrgd[a/b] and /dly_pwrgd[a/b] output signals to be asserted low and cause the /fault_main[a/b], the /fault_aux[a /b], the /int, and the syspwrgd output signals to their open-drain state.
micrel, inc. mic2342/2342r june 2008 8 m9999-062008-a pin description (cont.) pin number pin name pin function 47 40 /dly_pwrgda /dly_pwrgdb /dly_pwrgd[a/b] are open-drain, asserted active-low digital outputs that are normally connected by an external 10k ? pull-up resistor (each) to vstby or to a local logic supply. each output signal is asserted approximately 164 ms after their respective /pwrgd[a/b] output signals are asserted. the /dly_pwrgd[a/b] output signals are de-asserted when the /pwrgd[a/b] outputs are de-asserted or upon a high-to -low transition on the on[a/b] or auxen[a/b] inputs. there is approxim ately a 1-ms delay between the de- assertion of /dly_pwrgd[a/b] and its corresponding /pwrgd[a/b] digital outputs. please consult the /pwrgd[a/b] and /dly_pwrgd[a/b] state diagrams within the applications information section for more detail. 46 syspwrgd system power is good. syspwrgd is an open-drain, active-high digital output that is normally connected by an external 10k ? pull-up resistor to vstby or to a local logic supply. the syspw rgd output signal is asserted low when: (1) /crsw[a] is asserted, on[a] is asserted, /force_on_a is high, and either main 12v[a] or main 3v[b] output is below its output power-good threshold; (2) /crsw[b] is asserted, on[b] is asserted, /focre_on_b is high, and either main 12v[b] or main 3v[b] output is below its output power-good threshold; (3) /crsw[a] is asserted, auxen[a] is asserted, /force_on_a is high, and the vauxa output is below its output power-good threshold; or (4) /crsw[b] is asserted, auxen[b] is asserted, /force_on_b is high, and vauxb output is below its power-good threshold. for all other conditions, the syspwrg d output is open-drain. for more information with respect to the syspw rgd output signal, please consult the ?functional description? section. 38 /int interrupt output: this open-drain, asserted active-low digital output is normally connected by an external 10k ? resistor to vstby or a local logic supply. this signal is asserted whenever a power fault is detected. check ing the status of /fault_main[a/b] or /fault_aux[a/b] output will determine which slot and which rail caused the interrupt. to de-assert this signal output, please follow instructions provided on /fault_main[ a/b] and /fault_aux[a/b] output pin descriptions. 17 33 45 agnd 3 pins, ic ground connections: tie directly to the system?s analog gnd plane directly at the device. 7 18 19 20 30 nc reserved: make no external connections to these pins.
micrel, inc. mic2342/2342r june 2008 9 m9999-062008-a absolute maximum ratings (1) 12vin[a/b], 12vsense[a/b], 12vgate[a/b], 12vout[a/b] .....................................................14v 3vin[a/b], 3vsense[a/b], 3vgate[a/b], 3vout[a/b], vstby[a/b], vaux[a/b] .......................7v digital inputs on[a/b], auxen[a/b], /crsw[a/b], /force_on[a/b] ..................?0.5v (min) to 3.6v (max) cfilter[a/b], rfilter[a&b] ...................................7v output current /pwrgd[a/b], /dly_pwrgd[a/b] /fault_main[a/b], syspwrgd, /int, /fault_aux[a/b] 10ma power dissipation ................................in ternally limited lead temperature (soldering) lead-free package (-xytq) ir reflow, peak ..................................260c +0 c/?5c storage temperat ure ...........................?65 c to +150c esd rating (3) human body model ............................................ 2kv machine m odel .................................................200v operating ratings (2) supply voltages 12vin[a/b].........................................11. 0v to 13.0v 3vin[a/b]...............................................3.0v to 3.6v vstby[a/b] ...........................................3.0v to 3.6v ambient temperature (t a ) ........................ 0c to + 70c junction temperature (t j ) .................................... 125c package thermal resistance tqfp ( ja ) ................................................. 76.8c/w electrical characteristics (4) 12v in[a/b] = 12v, 3v in[a/b] = 3.3v, v stby[a/b] = 3.3v, t a = 25c, unless otherwise noted. bold values specifications applies over the full operating temperature range from 0 c < t a < +70 c. symbol parameter condition min typ max units power control and logic sections i cc12 i cc3.3 i ccstby supply current /crsw[a/b] = low /force_on[a/b] = high aux_en[a/b], on[a/b ] = [l,h], [l,l] 1.8 0.6 2.8 3 2.5 5 ma ma ma v uvlo(12v) v uvlo(3v) v uvlo(stby) undervoltage lockout thresholds 12vin[a/b] 3vin[a/b] vstby[a/b] 12v in[a/b] increasing 3v in[a/b] increasing v stby[a/b] increasing 8 2.2 2.8 9 2.5 2.9 10 2.75 3.0 v v v v hysstby undervoltage lockout hysteresis vstby[a/b] 50 mv v hysuv undervoltage lockout hysteresis 12vin[a/b], 3vin[a/b] 180 mv v uvth(12v) v uvth(3v) power-good undervoltage thresholds 12vout[a/b] 3vout[a/b] 12vout[a/b] decreasing 3vout[a/b] decreasing 10.2 2.7 10.5 2.8 10.8 2.9 v v v uvth(vaux) power-good undervoltage threshold vaux[a/b] vaux[a/b] decreasing i aux = 600ma 2.7 2.8 2.9 v v hyspg power-good detect hysteresis 30 mv v gate(12v) 12vgate[a/b] voltage 0 1.5 v i gate(12vsink) 12vgate[a/b] pull-down current start cycle 15 25 35 a i gate(12vpullup) 12vgate[a/b] pull-up current (fault off) any fault condition (vdd ?vgate) = 2.5v 20 ma
micrel, inc. mic2342/2342r june 2008 10 m9999-062008-b dc electrical characteristics (4) 12v in[a/b] = 12v, 3v in[a/b] = 3.3v, v stby[a/b] = 3.3v, t a = 25c, unless otherwise noted. bold values specifications applies over the full operating temperature range from 0c < t a < +70c. symbol parameter condition min typ max units v gate(3v) 3vgate[a/b] voltage 12vin ?1.5 12vin v i gate(3vcharge) 3vgate[a/b] charge current start cycle 15 25 35 a i gate(3vsink) 3vgate[a/b] pull-down current (fault off) any fault condition v 3vgate = 2.5v 65 ma v filter cfilter[a/b] threshold voltage 1.20 1.25 1.30 v i filter cfilter[a/b] charging current v 12vin ? v 12vsense > v thilimit and/or v 3vin ? v 3vsense > v thilimit 1.80 2.5 5.0 a v thlimit current limit threshold voltages 12vin[a/b] supplies 3vin[a/b] supplies v 12vin ? v 12vsense v 3vin ? v 3vsense 45 45 50 50 57 57 mv mv v thfast 12vout[a/b] & 3vout[a/b] fast-trip threshold voltages v 12vin ? v 12vsense v 3vin ? v 3vsense mic2342-2ytq only 90 100 110 mv v thfast 12vout[a/b] & 3vout[a/b] fast-trip threshold voltages v 12vin ? v 12vsense mic2342-2ytq v 3vin ? v 3vsense MIC2342-3YTQ mic2342-5ytq 90 135 100 150 dis- abled 110 165 mv mv i 12vsense[a/b] 12vsense[a/b] input current 0.35 1 a i 3vsense[a/b] 3vsense[a/b] input current 0.35 1 a i lkg,off(12vin[a/b] 12vin[a/b] input leakage current vstby = vstby[a/b] = +3.3v; 12vin[a/b] = off; 3vin[a/b] = off 1 a i lkg,off(3vin[a/b] 3vin[a/b] input leakage current vstby = vstby[a/b] = +3.3v; 12vin[a/b] = off; 3vin[a/b] = off 1 a v il low-level digital input voltage on[a/b], auxen[a/b], /crsw[a/b], /force_on[a/b] 0.8 v v ih high-level digital input voltage on[a/b], auxen[a/b], /crsw[a/b], /force_on[a/b] 2.1 3.6 v v ol low-level digital output voltage /fault_aux[a/b], /int, /fault_main[a/b], /pwrgd[a/b] ,syspwrgd, /dly_pwrgd i ol = 3 ma 0.4 v
micrel, inc. mic2342/2342r june 2008 11 m9999-062008-b symbol parameter condition min typ max units i lkg(off) digital output off-state leakage current /fault_aux[a/b], /int, /fault_main[a/b], /pwrgd[a/b], syspwrgd /dly_pwrgd[a/b] 5 a r pullup internal pull-up resistors to vstby[a] /crsw[a/b],on[a/b], auxen[a/b] vstby[a/b] = +3.3v 45 k ? i pullup internal pull-up current to vstby[a] /force_on[a/b] vstby[a/b] = +3.3v 60 a r ds(aux) internal vaux[a/b] power mosfet channel resistance i ds = 375 ma; t j = 100 c 0.4 ? v off(12vout[a/b] 12vout[a/b] off-state output offset voltage on[a/b] = low, 12vout[a/b] = off, t j = 100 c 50 mv v off(3vout[a/b] 3vout[a/b] off-state output offset voltage on[a/b] = low, 3vout[a/b] = off, t j = 100 c 50 mv v off(vaux[a/b] vaux[a/b] off-state output offset voltage auxen[a/b] = low, vaux[a/b] = off, t j = 100 c 50 mv overtemperature shutdown and reset thresholds with overcurrent on slot (5) t j increasing, each slot t j decreasing, each slot 140 130 c c t ov overtemperature shutdown and reset thresholds, all other conditions (all outputs will latch off) (5) t j increasing, both slots t j decreasing, both slots 160 150 c c i aux(thresh) auxiliary output current limit threshold (figure 4) current which must be drawn from vaux to register as a fault 0.84 a i sc(tran) maximum transient short circuit current vaux[a/b] enabled, then grounded a i lim(aux) regulated current after transient from end of i sc(tran) to cfilter time-out 0.375 0.7 0.975 a r dis(12v) r dis(3v) r dis(vaux) output discharge resistance 12vout[a/b] 3vout[a/b] 3vaux[a/b] 12v out[a/b] = 6.0v 3v out[a/b] = 1.65v 3v aux[a/b] = 1.65v 160 0 150 430 ? ? ?
micrel, inc. mic2342/2342r june 2008 12 m9999-062008-b ac electrical characteristics (4) 12v in[a/b] = 12v, 3v in[a/b] = 3.3v, v stby[a/b] = 3.3v, t a = 25c, unless otherwise noted. bold values specifications applies over the full operating temperature range from 0c < t a < +70c. symbol parameter condition min typ max units t off(12v) 12v current limit response time (5) (figure 2) mic2342-2ytq cgate[a/b] = 25pf v in ?v sense = 140mv 1 2.0 s t off(3v) 3.3v current limit response time (5) (figure 3) mic2342-2ytq cgate[a/b] = 25pf v in ?v sense = 140mv 1 2.0 s t sc(tran) vaux[a/b] current limit response time (figure 5) vaux[a/b] = 0v, vstby[a/b] = +3.3v 2.5 5 s t prop(12vfault) delay from 12vout[a/b] overcurrent limit to /fault_main[a/b] = low (5) mic2342-2ytq cfilter[a/b] = open v in ?v sense = 140mv 1 s t prop(3vfault) delay from 3vouta/b] overcurrent limit to /fault_main[a/b] = low (5) mic2342-2ytq cfilter[a/b] = open v in ?v sense = 140mv 2 s t prop(vauxfault) delay on vaux[a/b] overcurrent from cfilter ?time out? (v cfilter = v filter ) to /fault_aux[a/b] = low (5) mic2342-2ytq limit to /fault_aux[a/b] output cfilter[a/b] = 50pf v aux output grounded 10 s t lpw on[a/b], auxen[a/b] low pulse width to reset output upon fault removal (5) on[a/b], auxen[a/b] = high-to-low-high 200 ns t intclk digital filter (internal clock) period 5 15 s t por mic2342 power-on reset time after vstby[a/b] becomes valid (5) 80 255 s t /crsw[a/b] /crsw[a/b] debounce delay time 5.10 15.85 ms t /pwrgd /pwrgd[a/b] de-assertion delay time on[a/b] or auxen[a/b] high-to-low transition 640 2040 s t /dly_pwrgd /dly_pwrgd[a/b] assertion delay after /pwrgd[a/b] assertion on[a/b], auxen[a/b] = high, 12vout[a/b], 3vout[a/b], vaux[a/b] = valid; 80 241 ms t dflt internal primary oc detector response time (mic2342 and mic2342r) cfilter[a/b] = gnd 20.5 41 63.5 ms t auto retry auto retry period (mic2342r only) 410 1236 ms notes: 1. exceeding measurements given within the ?absolut e maximum ratings? section may damage the device. 2. the device is not guaranteed to function outside of the measurements given in the ?operating ratings? section. 3. these devices are esd sens itive. employ proper handling precautions. the hbm is 1.5k ? in series with 100pf. 4. specifications apply to packaged product only. 5. parameters guaranteed by des ign, not subject to test.
micrel, inc. mic2342/2342r june 2008 13 m9999-062008-b timing diagrams 6v 12vgate v thfast v thilimit t off(12v) v in ?v sense t 0v figure 1. 12v current limit response timing 1v 3vgate v thfast v thilimit t off(3v) v in ?v sense 0v t figure 2. 3v current limit response timing i out(aux) i out(aux) i lim(aux) must trip may not trip i aux(thresh) i 0 t figure 3. vaux current limit threshold
micrel, inc. mic2342/2342r june 2008 14 m9999-062008-b i out(aux) t sc(tran) i lim(aux) i sc(tran) i 0 t figure 4. vaux current limit response timing
micrel, inc. mic2342/2342r june 2008 15 m9999-062008-b functional diagram mic2342/mic2342r block diagram
micrel, inc. mic2342/2342r june 2008 16 m9999-062008-b typical characteristics
micrel, inc. mic2342/2342r june 2008 17 m9999-062008-b typical characteristics (cont.)
micrel, inc. mic2342/2342r june 2008 18 m9999-062008-b functional description hot swap insertion when circuit boards are inserted into systems carrying live supply voltages (?hot-plugge d?), high inrush currents often result due to the char ging of bulk capacitance that resides across the circuit board?s supply pins. this transient inrush current can cause the system?s supply voltages to temporarily 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 mic2342 addresses these issues by limiting the inrush currents to the l oad (pci express board), and thereby controlling the rate at which the load?s circuits turn-on. in addition to this inrush current control, the mic2342 offers input and output voltage supervisory functions and current limiting to provide robust protection for both the system and circuit board. system interface the mic2342 employs a hardware system interface that includes: on[a/b], auxen[a/b], /crsw[a/b], /fault_main[a/b], /fault_aux[a/b], /pwrgd[a/b], /int, and syspwrgd. power-on reset vstby[a/b] are the main power supply for the mic2342?s internal logic circuits and state machines . vstby[a/b] is required for proper operation of the mic2342?s internal logic circuitry and must be applied at all times. a power-on reset (por) cycle is initiated after vstby[a/b] is higher than its v uvlo(stby) threshold voltage and remains valid at that voltage for at least 80s. all internal logic flags are cleared after por. if the vstby[a/b] pin voltages are cycled on-off-on, a new power-on-reset cy cle is initiated. v stby must be the first supply input applied followed by the main supply inputs of 12v in and 3v in . during t por , all outputs remain off. in most applications, the total por interval will consist of the time required to charge the v stby input (bypass) capacitance to the uvlo threshold plus the internal t por delay time. the following equation is used to approximate the total por interval: () (s) t 10 (a) i v c t por 6 y) charge(stb ulvo(stby) stby(f) s) por_total( + ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? = ? where c stby is the v stby input bulk bypass capacitance and i charge(stby) is the current supplied by the v stby source to charge the capacitance. +12vout[a/b] and +3vout[a/b] start-up cycles all four of the mic2342?s +12v and +3v gate drive circuits have been designed to drive the gates of external power mosfets. the +12v gate drive circuits have been designed to drive p-channel mosfets and the +3v gate drive circuits are intended to drive n- channel mosfets. a list of recommended n- and p- channel power mosfets suited for use with the mic2342 and pci express applications can be found in table 2. these gate drive circuits have also been designed to limit inrush current in one of two modes: (1) by controlling the 12vgate[a/ b] or the 3vgate[a/b] voltage slew rates (dv 12gate[a/b] /dt or dv 3gate[a/b] /dt) or (2) by actively limiting the inru sh current, thereby charging the corresponding load capacitance in current limit. the mode that the mic2342 aut omatically enters is dependent upon the magnitude of the inrush current and the magnitude of the load capacitance at 12vout[a/b] and 3vout[a/b]. mode 1: [12v/3v]gate[a/b] slew rate control when a slot?s main supply voltages (12vout[a/b] and 3vout[a/b]) are off, each of the 12vgate[a/b] pins is held at 12vin[a/b] by an internal pull-up transistor. similarly, each 3vgate[a/b] pin is internally held at agnd. when the main s upply voltages are enabled by a low-to-high transition on the on[a/b] input pins (recall that the /crsw[a/b] inputs mu st also be asserted), the 12vgate[a/b] and the 3vgate[a/b] pins are each connected to an internal constant current supply, typically 25 a each. at eac h 12vgate[a/b] pin, this constant current supply is a current sink; at each 3vgate[a/b] pin, the supply is a current source. for applications where the inrush current is controlled by the 12vgate[a/b] voltage rate of change, an expression for the circuit?s behavior is given by the following equation: issp issp te) gate(12vga b] 12vgate[a/ c 25a c i dt dv = = where c issp = p-channel power mosfet gate input capacitance. for example, a si4435bdy (a 30-v p-channel power mosfet) exhibits an approximate c issp of 1700pf at v ds = 12v. the 12vgate[a/b] pin voltage rate-of- change (slew rate) would be: ms v 14.7 1700pf 25a c i dt dv issp k) gate(12vsn b] 12vgate[a/ = = = the 12vout[a/b] inrush current to the load while the 12vgate[a/b] voltage is ramping is dependent on c load(12vout[a/b]) and c issp . an expression for the 12vout[a/b] inrush current is given by:
micrel, inc. mic2342/2342r june 2008 19 m9999-062008-b issp t[a/b]) load(12vou k) gate(12vsn t[a/b]) load(12vou b] 12vgate[a/ out[a/b]) inrush(12v c c i c dt dv i = = for the same p-channel power mosfet in the previous example, if c issp = 1700pf and c load(12vout[a/b]) = 100f, the 12vout[a/b] inrush current charging this load capacitance is: a pf f a i b a vout inrush 47 . 1 1700 100 25 ]) / [ 12 ( = = calculating the 12vout[a/b] voltage rate-of-change for a given capacitive load can be determined by the following expression: ]) / [ 12 ( ]) / [ 12 ( ] / [ 12 b a vout load b a vout inrush b a vout c i dt dv = and, using the same quantities in the current example, is given by: ms v 14.7 f 100 a 1.47 dt dv ] 12vout[a/b = = to determine (to first-order) the time point at which the 12vout[a/b] voltage crosses its corresponding output ?power good? threshold, the following equation can be used: ( ) ms ms v v dt dv v v t b a vout hyspg v uvth b a vout pwrgd 72 . 0 7 . 14 53 . 10 ] / [ 12 ) 12 ( ]) / [ 12 ( = + = to determine 3vgate[a/b] pin voltage slew rates, inrush currents, 3vout[a/b] output voltage slew rates, and time to assert its corresponding internal ?power good? flag into capacitive loads connected to 3vout[a/b], simple computations can be made using the same equations by substituting i gate(3vcharge) for i gate(12vsink) , c issn (the input gate capacitance of an n- channel power mosfet) for c issp , c load(3vout[a/b]) for c load(12vout[a/b]) , i inrush(3vout[a/b]) for i inrush(12vout[a/b]) , and v uvth(3v) for v uvth(12v) . for example, if a si4420bdy n-channel power mosfet is used with the mic2342 to control inrush currents at 3vout[a/b], its c issn is approximately 4100pf at v ds = 3v. the 3vgate[a/b] pin voltage rate of change is given by: ms v 6.1 4100pf a 25 c i dt dv issn rge) gate(3vcha ] 3vgate[a/b = = = assuming a 300-f capacitive load, the 3vout[a/b] inrush current charging this load capacitance is given by: a 1.82 4100pf f 300 a 25 i ut[a/b]) inrush(3vo = = the 3vout[a/b] output voltage slew rate is given by: ms v 6.1 f 300 a 1.82 dt dv 3vout[a/b] = and the time to assert the in ternal 3vout[a/b] ?power good? flag is given by: ( ) = + = mode 2: charging 12vout and 3vout capacitive loads in current limit in x4 and x8 pci express applications, capacitive loads at 12vout[a/b] and 3vout[a/ b] can be as large as 1000f. as a result, the inrush load charging currents at start-up can be large enough to cause a voltage drop across the external sense resistor larger than 50mv. in these applications, internal servo circuits at 12vgate[a/b] and 3vgate[a/b ] modulate the drive to the gates of their corresponding power mosfets to regulate the load current to: /b] 12vsense[a /b] 12vsense[a thlimit ut[a/b]) limit(12vo r mv 50 r v i = = in the typical application circuit, the external sense resistor connected between 12vin[a/b] and 12vsense[a/b] pins was selected to be 20m ? . the regulated current charging the load capacitance at 12vout[a/b] is given by: a 2.5 m 20 mv 50 i ut[a/b]) limit(12vo = ? = once current-regulation control is activated, the circuit breaker?s t flt timer is also activated to protect the external power mosfet against potentially excessive power dissipation. for additional information on this timer and the mic2342?s circ uit breaker operation, please consult the section labeled ?circuit breaker function.? the output voltage rate of change at 12vout[a/b] during current limit charging into a 1000f capacitive load is given by: ms v 2.5 f 1000 a 2.5 c i dt dv t[a/b]) load(12vou ut[a/b]) limit(12vo ] 12vout[a/b = = = in this fashion, the inrush current is controlled and the load capacitance is charged up slowly during the start-up cycle. the gate driv e circuits will maintain control of the inrush current until the 12vout[a/b] or 3vout[a/b] voltages have reached their corresponding ?power good? thresholds (v uvth(12v)[a/b] or v uvth(3v)[a/b] , respectively) at which time the inrush current approaches its nominal steady-state level, the voltage across the external sense resi stor drops below the circuit breaker?s v thlimit threshold, and the corresponding internal ?power-is-good? flag is asserted. for the 12vout[a/b] example, its inte rnal ?power-is-good? flag is asserted at: ( ) = + = calculating the current limit for charging the 3vout[a/b] load capacitance, the output voltage slew rate at
micrel, inc. mic2342/2342r june 2008 20 m9999-062008-b 3vout[a/b], and when the inte rnal 3vout[a/b] ?power good? flag is asserted is a simple matter of substituting r 3vsense[a/b] for r 12vsense[a/b] , c load(3vout[a/b]) for c load(12vout[a/b]) , and v uvth(3v) for v uvth(12v) . even though individual internal ?power good? flags may be asserted, the conditions under which the mic2342?s external /pwrgd[a/b] and /dly_pwrgd[a/b] digital outputs are asserted is descri bed in the section labeled ?/pwrgd[a/b] and /dly_pwrgd[a/b] digital outputs.? power-down cycle when a slot is turned off, resistors internal to the mic2342/mic2342r are connected to each of the outputs to provide a disc harge path for capacitors connected to the part?s outputs. the nominal output discharge resistance values for each rail are found in the ?electrical characteristics? table. use of an external gate capacitor to control inrush current profile in pci express applications where the 12vout[a/b] and the 3vout[a/b] maximum load capacitance is 1000 f (2000uf on the 12v rail for x16 modules), the pci express power control specific ation clearly states that any inrush current rate-of-change shall not exceed 0.1a/s. this situation is most likely to happen when the controller is charging these large load capacitances in current limit. under these circumstances, it may be preferable to modify the gate drive by using gate voltage control instead of active current regulation to charge the load. as shown in figure 5, an external capacitor connected from each 3vgate[a/b] to agnd can be used. for the 12vgate[a/b], an optional miller capacitor (gate-drain) can be used in conjunction with a gate-source capacitor to fo rm a miller integrator to control the output slew rate. the optimal capacitor value is best determined empirically as the magnitude of the inrush current slew rate is a function of the power mosfet?s input capacitance (c iss ), the load capacitance (c load(3vout[a/b]) and c load(12vout[a/b]) ), and the current-limit sense resistor (r 3vsense[a/b] and r 12vsense[a/b ). using an external capacitor to control the gate voltage slew rate for large load capacitance may affect the mic2342/mic2342r?s specified system turn- on and turn-off time performance. figure 5. (optional) external gate slew control components
micrel, inc. mic2342/2342r june 2008 21 m9999-062008-b standby mode standby mode is entered when one or more of the main supply inputs (12vin and/ or 3vin) are below its respective uvlo threshold or off. the mic2342 also supplies 3.3v auxiliary output s (vaux[a/b]), satisfying pci express specifications. these outputs are fed via the vstby[a/b] input pins and controlled by the auxen[a/b] input pins. these outputs are independent of the main outputs (12vin[a/b] and 3vin[a/b]). should the main supply inputs move below their respective uvlo thresholds, vaux[a/b] w ill still function as long as vstby[a/b] is present. prior to standby mode, ona and onb inputs should be de-asse rted or the mic2342 will assert the /fault_main[a/b] and /int output signals, if an undervoltage condition on the main supply inputs is detected. circuit breaker function the mic2342 provides an el ectronic 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 (i lim = 50mv/r sense ) for a duration greater than t flt , the circuit breaker is tripped and both main supplies (all outputs except vaux[a/b]) are shut off. should the load current ca use a main output?s v sense to exceed v thfast , the outputs are immediately shut off with no delay. undervoltage condi tions 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 a different circuit-breaker function. the vaux[a/b] circuit breakers do not incorporate a fast-trip detect or, instead they regulate the output current into a fault to avoid exceeding their operating current limit. the circ uit breaker will trip due to an overcurrent on vaux[a/b] when the fault timer expires, shutting down the vaux output and both main outputs of the affected slot. the aux output dependence for the main supplies during an aux fault is inherent in the mic2342/mic2342r but does not apply for the mic2341/mic2341r. this use of the t flt timer prevents the circuit breaker from tripping prematurely due to brief current transients. following a fault condition, the outputs can be turned on again by toggling the on[a/b] input high-low-high (if the fault occurred on one of the main outputs), or similarly toggling the auxen[a/b] input (if the fault occurred on the aux outputs), or by cycling both on[a/b] and auxen[a/b] (if faults occurred on both the main and aux outputs). when the circuit breaker trips, the corresponding /fault_main[a/b] or /fault_aux[a/b] will be asserted. at the same time, /int will be asserted. note that /int is only de-as serted by applying a high-to- low transition on the corresponding slot?s on[a/b] or auxen[a/b] input. the response time (t flt ) of the mic2342?s primary overcurrent 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 slot b, cfilter[b] is located at pin 35. for a given response time, the value for c filter[a/b] is given by: 3 filter filter flt[a/b] ] filter[a/b 10 (v) v (a) i (ms) t (f) c = where t flt[a/b] is the desired response time and quantities i filter and v filter are specified in the mic2342?s ?electrical characteristics? table. digital filter and auto-retry functions new timers have been incorporated for additional protection for overcurrent situations. in many applications, external power mosfets used at 12vout[a/b] and at 3vou t[a/b] have been damaged during initial start-up and ov ercurrent conditions because the response time of the primary oc detectors was set too long (that is, an incorrect value for cfilter[a/b] was used). in these product s, a digital filter delay counter is introduced, and is internally set to a typical delay time of 40ms. as show n in the typical applications circuit of the mic2342, an external capacitor from cfilter[a/b] to ground is used to set the response time of the primary overcurrent detectors to t flt . at the time a large inrush current causes the primary oc detector to sense an over current condition, a cfilter[a/b] charge-up sequen ce is initiated. at the same time, the mic2342?s digita l filter delay counter is also initiated and commences a count-up to 40ms. the mic2342?s internal logic circuits have been designed to trip the circuit breaker after t flt or t dflt , whichever delay is smaller. if the overcu rrent condition causes the electronic circuit breaker to latch off and thereby asserting a fault conditi on, the mic2342 remains latched-off awaiting system intervention (by toggling on[a/b] and/or auxen[a/b] and/or cycling the input power supplies). internal to the mic2342r only, a second, or auto-retry, delay counter is initiated and commences a count-up to approximately 820ms to allow the external power mosfet to cool before attempting another power-up seque nce. figure 6 illustrates the filter responses during an overcurrent fault.
micrel, inc. mic2342/2342r june 2008 22 m9999-062008-b figure 6. mic2342r auto-retry timing diagram and operation in very cost-sensitive applications, the system design engineer can save the cost of the (2) external cfilter[a/b] capacitors by using only the digital filter and/or the auto-retry delay counters. this mode is automatically invoked by c onnecting the mic2342 or the mic2342r?s cfilter[a/b] pins directly to agnd. in this configuration, the primary oc detectors? response time t flt is equal to t dflt (or 40ms as above) in figure 7, the gate drive circuits have taken control and regulate the inrush current to charge the load capacitances in current limit. once the internal digital filter delay counter terminates, the circuit breaker trips off. as in the previous case, the mic2342 latches off and the mic2342r initiates the auto-r etry delay counter to count up to 820ms before attempti ng another power-up cycle.
micrel, inc. mic2342/2342r june 2008 23 m9999-062008-b figure 7. mic2342r auto-retry timing diagram and operation in current-limit thermal shutdown the internal vaux[a/b] mosfets are protected against damage not only by current limiting, but by overtemperature protection as well. should an overcurrent condition on ei ther vaux[a] or vaux[b] raise the junction temperature of the mic2342 to 140c, all of the outputs for that co rresponding slot (including vaux) will be shut off and that slot?s /fault_aux output will be asserted. the sl ot?s /fault_main output will not be asserted. the other slot?s operat ing condition will remain unaffected. howe ver, should the mic2342?s die temperature exceed 160c because of an overcurrent fault condition on both vaux[a] and vaux[b], both slots (all outputs, including vauxa and vauxb) will be shut off. in this case, both /fault_aux[a/b] output signals will be asserted; the /fault_main[a/b] output signals will not be asserted. plug-in card retention switch inputs two pins on the mic2342 are available for use as card retention switch inputs, / crsw[a/b]. these pins are internally pulled-up by 45k ? resistors to vstby and prevent the enabling of all gate drive circuits on 12gate[a/b], 3vgate[a/b], and vaux[a/b] unless these input pins are asserted low. in addition, each of these inputs exhibits an internal debounce delay time of approximately 10ms. /force_on[a/b] inputs these level sensitive, asserted active-low digital inputs are internally pulled up to vstby through a weak current source and are intended for diagnostics during the debug phase of the system design involving the mic2342. in asserting /fo rce_on[a/b] low, all three of the respective slot?s out puts (+12v, +3.3v, and vaux) will turn on. however, all protections for those outputs are disabled. this explicitly includes all overcurrent and short circuit protections, and on-chip thermal protection for the vaux supplies. additi onally, asserting a slot?s /force_on[a/b] input will di sable all of its input and output uvlo protections, with the sole exception of that asserting either or both of the /force_on[a/b] inputs will not disable the vstby[a/b] input uvlo. asserting /force _on[a/b] low will cause the respective slot?s /pwrgd[a/b], and /dly_pwrgd[a/b] output signals to be asserted low while the /fault_main[a/b], the /fault_aux[a/b}, the /int, and the syspwrgd output signal s to enter their open- drain state.
micrel, inc. mic2342/2342r june 2008 24 m9999-062008-b /pwrgd[a/b] and /dly_pwrgd digital outputs the mic2342 has two /pwrgd outputs and two /dly_pwrgd outputs, one for each slot. these are open-drain, active-low outputs that are activated after power-on-reset and are normally connected by an external 10k ? resistor to v stby or a local logic supply. each /pwrgd[a/b] output is asserted when a slot has been enabled and has successfully begun delivering power to its respective +12v, +3.3v, and vaux outputs. the /dly_pwrgd[a/b] output s are asserted 164ms after its corresponding /pwrgd[a/b] output. an equivalent logic diagram for /pwrgd[a/b] is shown in figure 8 with their corr esponding state diagrams. figure 8. state diagrams for /pwrgd[a/b] and /dly_pwrgd[a/b] syspwrgd digital output syspwrgd is an open-drain, asserted active-high digital output provided by t he mic2342 for additional slot status information to the se rvice or system processor. this output is normally c onnected by an external 10k ? resistor to v stby or a local logic supply. there is one syspwrgd output for each mic2342 and this signal becomes activated after power-on-reset. this signal is asserted unless at least one pc ie slot is occupied, either on[a/b] and/or auxen[a/b] of the slot in question is asserted, either /force _on[a/b] inputs are not asserted, and the output volt ages at the load are lower than respective power-is-good output threshold voltages. functionality of the syspwrgd output signal has been designed to accommodate single- and dual- slot applications as well as applications where the main[a/b] outputs are used , but the vaux[a/b] outputs are not. in multiple mic2342 applications where one or more pcie slots are unused and one or multiple on[a/b] and auxen[a/b] input signals are not asserted, each syspwrgd digital output will appear asserted facilitating an ?or-tying? of all syspwrgd output signals, thereby ensuring correct logic functionality across the entire system. see table 1 for the syspwrgd truth table.
micrel, inc. mic2342/2342r june 2008 25 m9999-062008-b ona auxena /crswa /force_ona 12v out main a 3v out main a vaux a onb auxenb /crswb /force_onb 12v out main b 3v out main b vaux b syspwrgd 1 x 0 1 uv x x x x x x x x x 0 1 x 0 1 x uv x x x x x x x x 0 x 1 0 1 x x uv x x x x x x x 0 x x x x x x x 1 x 0 1 uv x x 0 x x x x x x x 1 x 0 1 x uv x 0 x x x x x x x x 1 0 1 x x uv 0 where ?1? = logic high ?0? = logic low ?x? = don?t care table 1. syspwrgd truth table hardware interface once the input power supply voltages are above their respective uvlo thresholds, the mic2342/mic2342r?s hardware interface can be enabled for power control by asserting the control i nput pins (/crsw[a/b], auxen[a/b], and on[a/b]) app ropriately for each slot. the mic2342/mic2342r?s on[a/b] and auxen[a/b] signals are asserted active-high, level-sensitive digital inputs with internal pull-up 45k ? resistors to vstby[a] to save pc board area and ex ternal component costs. as such, external hot-plug controllers connecting to these pins should configure their re spective output drivers to open-drain and configure their firmware to de-assert these signals to turn off either the main[a/b] outputs or the vaux[a/b] outputs. as these input control signals are already asserted after por, the corresponding /crsw[a/b] control signal should be used to enable the slot?s gate drive circuits to initiate a power-up sequence. for example, in order for the mic2342/mic2342r to switch on the vaux supply for either slot, the auxen[a/b] control can be enabled during or after the power-on-reset operation (typically, t por = 160 s. the timing response diagram of figure 9 illustrates the hardware interface operation where an overcurrent fault is detected by the mic2342/mic2342r controller after initiating a power-up sequence. the main (+12v & +3.3v) and vaux[a/b] suppl y rails, /fault, /pwrgd and /int output responses for both aux and main are shown in the figure.
micrel, inc. mic2342/2342r june 2008 26 m9999-062008-b figure 9. mic2342 output signals? shutdown r esponses during aux and main overcurrent faults
micrel, inc. mic2342/2342r june 2008 27 m9999-062008-b slot[a/b] fault reporting the mic2342?s /fault_mai n[a/b] open-drain digital output are activated after power-on-reset and become asserted when: the on[a/b] input signals are asserted, and ? the 12vin[a/b] or the 3vin[a/b] input voltages is less 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 corresponding c filter[a/b] timeout or the digital filter delay has expired. in order to clear the /fault_main[a/b] outputs once asserted and to reset the corresponding circuit breaker(s), a high-to-low transition is required on the on[a/b] input signals. please see /fault_main[a/b] pin descriptions for additional information. figure 10. state diagram for /fault_main[a/b] signals the mic2342?s /fault_aux[a/b] open-drain digital outputs are activated after power-on-reset and become asserted when: the auxen[a/b] input signals are asserted, and ? the slow vaux[a/b] oc circuit breaker has tripped and its corresponding c filter[a/b] timeout or the digital filter delay has expired, or ? the slow vaux[a/b] oc circuit breaker has tripped and the slot[a/b] die temperature is higher than 140c, or ? the mic2342?s global die temperature is higher than 160c in order to clear the /fault_aux[a/b] outputs once asserted and to reset the vau x[a/b] circuit breaker(s), a high-to-low transition is required on the auxen[a/b] input signals. please see /fault_aux[a/b] pin descriptions for additional information. if the /force_on[a/b] digital inputs are used for diagnostic purposes, the /fault_main[a/b], /fault_aux[a/b], /pwrgd[a/b], and /dly_pwrgd[a/b] digital outputs are de-asserted once /force_on[a/b] i nputs are asserted. figure 11. state diagram for /fault_aux[a/b] signals
micrel, inc. mic2342/2342r june 2008 28 m9999-062008-b applications information sense resistor selection the 12v and the 3.3v supplies employ internal current sensing circuitry to detect ov ercurrent conditions that may trip the circuit breaker. an external sense resistor is used to monitor the current that passes through the external mosfet for each slot of the 12v and 3.3v rails. the sense resistor is nominally valued at: limit thlimit sense(nom) i v r = where v thilimit is the typical (or nominal) circuit breaker threshold voltage (50mv) and i limit is the nominal inrush load current level to trip the internal circuit breaker. to accommodate worse-case tolerances in the sense resistor (for a 1% initial to lerance, allow 3% tolerance for variations over time and temperature) and circuit breaker threshold voltages, a slightly more detailed calculation must be used to determine the minimum and maximum hot swap load currents. as the mic2342?s minimum current limit threshold voltage is 45mv, the minimu m hot swap load current is determined where the sense resistor is 3% high: sense(nom) sense(nom) limit(min) r 43.7mv ) r (1.03 45mv i = = keep in mind that the minimum hot swap load current should be greater than the application circuit?s upper steady-state load current boundary. once the lower value of r sense has been calculated, it is good practice to check the maximum hot swap load current (i limit(max) ) which the circuit may let pass in the case of tolerance build-up in the opposite direct ion. here, the worse-case maximum is found using a v thilimit(max) threshold of 55mv and a sense resistor 3% low in value: sense(nom) sense(nom) limit(max) r 56.7mv ) r (0.97 55mv i = = in this case, the application circuits must be sturdy enough to operate up to approximately 1.25x the steady- state hot swap load currents. for example, if one of the 12v slots of the mic2342 ci rcuit must pass a minimum hot swap load current of 1. 5a without nuisance trips, r sense should be set to: 30m ? 1.5a 45mv r sense(nom) = = where the nearest 1% standard value is 30.1m ? . at the other tolerance extremes, i limit(max) for the circuit in question is then simply: 1.88a 30.1m ? 56.7mv i limit(max) = = with a knowledge of the application circuit?s maximum hot swap load current, the power dissipation rating of the sense resistor can be determined using p = i 2 r. here, the current is i limit(max) = 1.88a and the resistance r sense(max) = (1.03)(r sense(nom) ) = 31.00m ? . thus, the sense resistor?s maximum power dissipation is: p max = (1.88a) 2 x (31.00m ? ) = 0.110w a 0.25w sense resistor is a good choice in this application. pcb layout suggestions and hints 4-wire kelvin sensing because of the low value required for the sense resistor, special care must be used to accurately measure the voltage drop across it. spec ifically, the measurement technique across r sense must employ 4-wire kelvin sensing. this is simply a means of ensuring that any voltage drops in the power traces connected to the resistors are not picked up by the signal conductors measuring the voltages across the sense resistors. figure 12 illustrates how to implement 4-wire kelvin sensing. as the figure shows, all the high current in the circuit (from v in through r sense and then to the drain of the n-channel power mosfet) flows directly through the power pcb traces and through r sense . the voltage drop across r sense is sampled in such a way that the high currents through the power traces will not introduce significant parasitic voltage drops in the sense leads. it is recommended to connect the hot swap controller?s sense leads directly to the sense resistor?s metalized contact pads. the kelvin s ense signal traces should be symmetrical with equal length and width, kept as short as possible, and isolated from any noisy signals and planes. additionally, for designs that implement kelvin sense connections that exceed 1" in length and/or if the kelvin (signal) traces are vulnerable to noise possibly being injected onto these signals, t he example circuit shown in figure 13 can be implemented to combat noisy environments. this circuit implements a 1.6 mhz low- pass filter to attenuate higher frequency disturbances on the current sensing circuitry. however, individual system analysis should be used to determine if filtering is necessary and to select t he appropriate cutoff frequency for each specific application. other layout considerations figure 14 is a suggested pcb layout diagram for the mic2342 power traces, kelvin sense connections, and capacitor components. in th is illustration, only the 12v slot b is shown but a similar approach is suggested for both slots of each main power rail (12v and 3.3v). many hot swap applications w ill require load currents of several amperes. therefore, the power (12vin and return, 3vin and return) trace widths (w) need to be wide enough to allow the current to flow while the rise in temperature for a given copper plate (e.g., 1oz. or 2oz.) is kept to a maximum of 10c to 25c. the return (or
micrel, inc. mic2342/2342r june 2008 29 m9999-062008-b power ground) trace should be the same width as the positive voltage power traces (input/load) and isolated from any ground and signal planes so that the controller?s power is common mode. also, these traces should be as short as possible in order to minimize the ir drops between the input and the load. as indicated in the pin description section, an external connection must be made that ties together both channel inputs ((+) kelvin sense) of each main power rail (i.e., 3vina and 3vinb, 12vina and 12vinb must be externally connected). these connections should be implemented directly at the chip. insure that the voltage drop between the two (+) kelvin sense inputs for each rail is no greater than 0.2mv by using a common power path for the two inputs (e.g., 12vina, 12vinb ). finally, the use of plated-through vias will be necessary to make circuit connection to the power, ground, and signal planes on multi-layer pcbs. figure 12. 4-wire kelvin sense connections for r sense figure 13. current limit sense filter for noisy systems
micrel, inc. mic2342/2342r june 2008 30 m9999-062008-b figure 14. suggested pcb layout for sense resistor, power mosfet, and capacitors
micrel, inc. mic2342/2342r june 2008 31 m9999-062008-b mosfet and sense resistor vendors device types, part numbers, and manufacturer contact information for power mosfets and sense resistors are provided in table 2. some of the recommended mosfets include a metal (tab) heat sink on the bottom side of the package. contact the device manufacturer for package information. key power mosfet type(s) mosfet vendors n-channel p-channel package contact information si4420dy si4435bdy so-8 si4442dy si4427bdy so-8 si3442dv si4405dy so-8 si4410dy si4425bdy so-8 si7860adp si7483adp powerpak so-8 si7344dp si7491dp powerpak so-8 si7844dp (dual) si7945dp (dual) powerpak so-8 si7114dn si7423dn 1212 so-8 vishay-siliconix si7806adn si7421dn 1212 so-8 www.siliconix.com (203) 452-5664 irf7882 irf7424 so-8 irf7413 irf7416 so-8 international rectifier irf7313 (dual) irf7328 (dual) so-8 www.irf.com (310) 322-3331 resistor vendors sense resistors contact information vishay - dale ?wsl? and ?wsr? series www.vishay.com/docswsl_30100.pdf (203) 452-5664 irc ?oars? series ?lr? series second source to ?wsl? www.irctt.com/pdf_files/oars.pdf www.irctt.com/pdf_files/lrc.pdf (828) 264-8861 table 2. mosfet and sense resistor vendors
micrel, inc. mic2342/2342r june 2008 32 m9999-062008-b package information 48-pin tqfp (t) micrel, inc. 2180 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 believ ed to be accurate and reliable. however, no responsibility is a ssumed by micrel for its use. micrel reserves the right to change ci rcuitry and specifications at any time without notification to the customer. micrel products are not designed or authori zed for use as components in life support app liances, devices or systems where malfu nction of a product can reasonably be expected to result in personal injury. life suppo rt devices or systems are devices or systems that (a) are in tended 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 significan t injury to the user. a purchaser?s use or sale of micrel products for use in life support appliances, devices or systems is a purchaser?s own risk and purchaser agrees to fully indemnify micrel for any damages resulting from such use or sale. ? 2007 micrel, incorporated.

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