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Final Electrical Specifications
LTC1643L/LTC1643H PCI-Bus Hot Swap Controller
September 1998
FEATURES
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DESCRIPTION
The LTC(R)1643 is a Hot SwapTM controller that allows a board to be safely inserted and removed from a live PCI-Bus slot. Two external N-channel transistors control the 3.3V and 5V supplies while on-chip switches control the -12V and 12V supplies. All supply voltages can be ramped up at a programmable rate. An electronic circuit breaker protects all four supplies against overcurrent faults. The fold-back current limit feature limits current spikes and power dissipation when shorts occur and allows boards with large capacitances to be powered up without tripping the circuit breaker. The PWRGD output indicates when all of the supply voltages are within tolerance and the FAULT output indicates an overcurrent condition. The ON(LTC1643H)/ON (LTC1643L) pin is used to cycle the board power or reset the circuit breaker. The LTC1643 is available in a 16-pin narrow SSOP package.
, LTC and LT are registered trademarks of Linear Technology Corporation. Hot Swap is a trademark of Linear Technology Corporation. CompactPCI is a trademark of PCI Industrial Computer Manufacturing Group.
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Allows Safe Board Insertion and Removal from a Live PCI Slot Works on either a Motherboard or CompactPCITM Card Controls -12V, 3.3V, 5V, 12V Supplies Programmable Fold-Back Current Limit with Circuit Breaker User-Programmable Supply Voltage Power-Up Rate High Side Drive for External N-Channels -12V and 12V On-Chip Switches Fault and Power-Good Outputs
APPLICATIONS
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PCI-Based Servers CompactPCI Compliant Boards
TYPICAL APPLICATION
Hot Swappable PCI Supply
R1 0.007 Q1 IRF7413 5V 5A
R2 0.005
Q2 IRF7413
R6 10
SYSTEM POWER SUPPLY 9 3VIN 8 GND 1 12VIN 2 VEEIN 5 ON PCI POWER SYSTEM CONTROLLER RESET R3 10k R4 10k 6 10
R5 10 11 3 13 12 5VSENSE 14 5VOUT
3VSENSE GATE
3VOUT 5VIN
12VOUT LTC1643H VEEOUT
FAULT TIMER
7
PWRGD
Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
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R7 1k
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3.3V 7.6A GND
C1 0.047F
16 15 4 C2 0.1F
12V 500mA -12V 100mA
LOGIC RESET
1643 TA01
1
LTC1643L/LTC1643H
ABSOLUTE MAXIMUM RATINGS
(Note 1)
PACKAGE/ORDER INFORMATION
TOP VIEW 12VIN 1 VEEIN 2 3VOUT 3 TIMER 4 ON/ON* 5 FAULT 6 PWRGD 7 GND 8 16 12VOUT 15 VEEOUT 14 5VOUT 13 5VIN 12 5VSENSE 11 GATE 10 3VSENSE 9 3VIN
Supply Voltages 12VIN ................................................................ 13.2V VEEIN .............................................................. -13.2V Input Voltage (Pin 5) ................ - 0.3V to (12VIN + 0.3V) Output Voltages (Pins 6, 7) ...... - 0.3V to (12VIN + 0.3V) Analog Voltages (Pins 3, 4, 9, 10 to 14) ........ - 0.3V to (12VIN + 0.3V) VEEOUT ............................................ -13.2V to + 0.3V 12VOUT .............................................. - 0.3V to 13.2V Operating Temperature Range Commercial ............................................. 0C to 70C Industrial ........................................... - 45C to 85C Storage Temperature Range ................. - 65C to 150C Lead Temperature (Soldering, 10 sec).................. 300C
ORDER PART NUMBER LTC1643HCGN LTC1643LCGN LTC1643HIGN LTC1643LIGN
GN PACKAGE 16-LEAD NARROW PLASTIC SSOP * ON FOR LTC1643H, ON FOR LTC1643L
TJMAX = 150C, JA = 135C/ W
Consult factory for Military grade parts.
DC ELECTRICAL CHARACTERISTICS
SYMBOL IDD VLKO PARAMETER V12VIN Supply Current Undervoltage Lockout CONDITIONS 12VIN 3VIN 5VIN
V12VIN = 12V, VEE = - 12V, V3VIN = 3.3V, V5VIN = 5V, TA = 25C (Note 2)
MIN
q q q q q q q q
TYP 3.5 9 2.5 2.5 7.5 53 7.5 53 15 - 50 200 10 100 250 250 120
MAX 8 10.8 2.75 2.75 12 65 12 65 - 100 20 200 600 750 250 500 1500 215 650 11.4 11.4 - 10.8 - 10.8 3.0 3.0 4.75 4.75
UNITS mA V V V mV mV mV mV s A A mA mV mV mV mV mA mA mA mA C V V V V V V V V
ON = 3V, ON = GND
7 2.25 2.25 4 40 4 40 - 20 3
VFB
Fold-Back Current Limit Voltage
VFB = (V5VIN - V5VSENSE), V5VOUT = 0V VFB = (V5VIN - V5VSENSE), V5VOUT > 2.5V VFB = (V3VIN - V3VSENSE), V3VOUT = 0V VFB = (V3VIN - V3VSENSE), V3VOUT > 1.3V Charge Pump On, VGATE = GND, FAULT = High Charge Pump Off, VGATE = 5V, FAULT = High Charge Pump Off, VGATE = 5V, FAULT = Low (V12VIN - VGATE) (V12VIN - V12VOUT), I = 500mA (VEEOUT - VEEIN), IEE = 100mA C Grade I Grade
tCB ICP
Circuit Breaker Trip Filter Time GATE Pin Output Current
q q
VGATE VDROP
External Gate Voltage Internal Switch Voltage Drop
q q q q q q q
ICL
Current Fold-Back
12VIN, 12VOUT = 0V 12VIN, 12VOUT = 12V VEEIN, VEEOUT = 0V VEEIN, VEEOUT = - 12V V12VOUT VEEOUT V3VOUT V5VOUT C Grade I Grade C Grade I Grade C Grade I Grade C Grade I Grade
50 525 100 225 10.8 10.4 - 10.2 - 10.0 2.8 2.75 4.5 4.4
250 850 160 450 150 11.1 11.1 - 10.5 - 10.5 2.9 2.9 4.65 4.65
TTS VTH
Thermal Shutdown Temperature Power-Good Threshold Voltage
q q q q q q q q
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LTC1643L/LTC1643H DC ELECTRICAL CHARACTERISTICS
SYMBOL VIL VIH VOL IIN PARAMETER Input Low Voltage Input High Voltage Output Low Voltage ON/ON Pin Input Current 5VSENSE Input Current 3VSENSE Input Current 5VIN Input Current 3VIN Input Current 5VOUT Input Current 3VOUT Input Current RDIS 5VOUT Discharge Impedance 3VOUT Discharge Impedance 12VOUT Discharge Impedance VEEOUT Discharge Impedance TIMER Pin Current TIMER Threshold Voltage CONDITIONS ON/ON, FAULT ON/ON, FAULT FAULT, PWRGD, I = 3mA ON/ON = GND ON/ON= 12VIN 5VSENSE = 5V 3VSENSE = 3V 5VIN = 5V 3VIN = 3V 5VOUT = 5V, ON = 3V, ON = GND 3VOUT = 3V, ON = 3V, ON = GND ON = GND or ON = 3V ON = GND or ON = 3V ON = GND or ON = 3V ON = GND or ON = 3V Timer On, VTIMER = GND Timer Off, VTIMER = 5V (V12VIN - VTIMER)
q q q q q q q q q q q q
V12VIN = 12V, VEE = - 12V, V3VIN = 3.3V, V5VIN = 5V, TA = 25C (Note 2)
MIN 2 0.4 0.08 0.08 50 50 460 320 240 220 100 70 450 1600 - 15 0.5 - 22 45 0.9 - 27 1.3 10 10 100 100 700 600 500 500 TYP MAX 0.8 UNITS V V V A A A A A A A A A mA V
ITIMER VTIMER
q
The q denotes specifications that apply over the full operating temperature range. Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired.
Note 2: All currents into device pins are positive; all currents out of device pins are negative. All voltages are reference to ground unless otherwise specified.
TYPICAL PERFORMANCE CHARACTERISTICS
3.3V and 5V Current Fold-Back Profile
11 10 9 8 7 6 5 4 3 2 1 0 0 1 RSENSE = 0.005 3 4 2 OUTPUT VOLTAGE (V)
OUTPUT CURRENT (A)
OUTPUT CURRENT (A)
5VOUT
0.5
OUTPUT CURRENT (A)
3VOUT
UW
5
1643 G01
12V Current Fold-Back Profile
1.0 1.0
- 12V Current Fold-Back Profile
0.5
0
0
2
6 8 4 OUTPUT VOLTAGE (V)
10
12
1643 G02
0
0
-2
-6 -8 -10 -4 OUTPUT VOLTAGE (V)
-12
1643 G03
3
LTC1643L/LTC1643H
PIN FUNCTIONS
12VIN (Pin 1): 12V Supply Input. It powers all the chip's internal circuitry. A 0.5 switch is connected between 12VIN and 12VOUT with a fold-back current limit. An undervoltage lockout circuit prevents the switches from turning on while the 12VIN pin voltage is less than 9V. VEEIN (Pin 2): - 12V Supply Input. A 1.2 switch is connected between VEEIN and VEEOUT with a fold-back current limit. 3VOUT (Pin 3): Analog Input. Used to monitor the 3.3V output supply voltage. The PWRGD signal cannot go high until the 3VOUT pin exceeds 3V. TIMER (Pin 4): Analog Current Fault Inhibit Timing Input. Connect a capacitor from TIMER to GND. With the chip turned off (ON = GND or ON = High) or the internal circuit breaker tripped (FAULT = GND), the TIMER pin is internally held at GND. When the chip is turned on, a 20A pull-up current source is connected to TIMER. Current limit faults will be ignored until the voltage at the TIMER pin rises to within 0.9V of 12VIN. ON/ON (Pin 5): Digital Input.The LTC1643L has an active low enable, ON, and the LTC1643H has an active high enable, ON. When the ON pin is pulled high or the ON pin pulled low, the GATE pin is pulled high by a 50A current source and the internal 12V and - 12V switches are turned on. When the ON pin is pulled low or the ON pin pulled high, the GATE pin will be pulled to ground by a 200A current source and the 12V and - 12V switches turned off. The ON/ON pin is also used to reset the electronic circuit breaker. If the ON/ON pin is cycled following the trip of the circuit breaker, the circuit breaker is reset and a normal power-up sequence will occur. FAULT (Pin 6): Open-Drain Digital I/O. FAULT is pulled low when a current limit fault is detected. Current limit faults are ignored while the voltage at the TIMER pin is less than 12VIN - 0.9V. Once the TIMER cycle is complete, FAULT will pull low 15s after any of the supplies go into current limit. At the same time the GATE and TIMER pins are pulled to GND and the 12V and -12V switches are turned off. The chip will remain latched in the off state until the ON/ON pin is toggled or the power is cycled. Forcing the FAULT pin low with an external pull-down will immediately turn off the internal switches and force the GATE and TIMER pins to GND independent of the state of the ON/ON pin. However, the chip is not latched into the off state, so when the FAULT pin is released, the state of the chip will be determined by the ON pin. PWRGD (Pin 7): Open-Drain Digital Power-Good Output. PWRGD remains low while V12VOUT 11.4V, V3VOUT 3V, V5VOUT 4.75V and VEEOUT - 10.8V. When one of the supplies falls below its power-good threshold voltage, PWRGD will go high after a 15s deglitching time. The switches will not be turned off when PWRGD goes high. GND (Pin 8): Chip Ground. 3VIN (Pin 9): 3.3V Supply Sense Input. An undervoltage lockout circuit prevents the switches from turning on when the voltage at the 3VIN pin is less than 2.5V. If no 3.3V input supply is available, tie 3VIN to the 5VIN pin. 3VSENSE (Pin 10): The 3.3V Current Limit Set Pin. With a sense resistor placed in the supply path between 3VIN and 3VSENSE, the GATE pin voltage will be adjusted to maintain a constant voltage across the sense resistor and a constant current through the switch. A fold-back feature makes the current limit decrease as the voltage at the 3VOUT pin approaches GND. To disable the current limit, 3VSENSE and 3VIN can be shorted together. GATE (Pin 11): High Side Gate Drive for the External N-Channels. Requires an external series RC network for the current limit loop compensation and setting the minimum ramp-up rate. During power-up, the slope of the voltage rise at the GATE is set by the 50A current source connected to 12VIN and the external capacitor connected to GND or by the 3.3V or 5V current limit and the bulk capacitance on the 3VOUT or 5VOUT suppy lines. During power-down, the slope of the falling voltage is set by the 200A current source connected to GND and the external GATE capacitor. The voltage at the GATE pin will be modulated to maintain a constant current with either the 3V or 5V supplies go into current limit. When a current limit fault occurs after the inhibit period set by the TIMER pin capacitance, the undervoltage lockout circuit on 3.3V, 5V or 12V trips or
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LTC1643L/LTC1643H
PIN FUNCTIONS
the FAULT pin is pulled low, the GATE pin is immediately pulled to GND. 5VSENSE (Pin 12): 5V Current Limit Set Pin. With a sense resistor placed in the supply path between 5VIN and 5VSENSE, the GATE pin voltage will be adjusted to maintain a constant voltage across the sense resistor and a constant current through the switch. A fold-back feature makes the current limit decrease as the voltage at the 5VOUT pin approaches GND. To disable the current limit, 5VSENSE and 5VIN can be shorted together. 5VIN (Pin 13): Analog Input. Used to monitor the 5V input supply voltage. An undervoltage lockout circuit prevents the switches from turning on when the voltage at the 5VIN pin is less than 2.5V. 5VOUT (Pin 14): Analog Input. Used to monitor the 5V output supply voltage. The PWRGD signal cannot go high until the 5VOUT pin exceeds 4.75V. VEEOUT (Pin 15): -12V Supply Output. A 1.2 switch is connected between VEEIN and VEEOUT. VEEOUT must exceed -10.8V before the PWRGD signal can go high. 12VOUT (Pin 16): 12V Supply Output. A 0.5 switch is connected between 12VIN and 12VOUT. 12VOUT must exceed 11.4V before the PWRGD signal can go high.
BLOCK DIAGRAM
5VIN 5VSENSE 13 12
2.5V UVL ON/ON 5 FAULT 6 Q3 PWRGD 7 Q4
Q5
200A
LOGIC
12VIN 9V UVL Q1 Q9 20A CP7 Q6 + Q2 Q10
REF
CP5
REF
1643 BD
1 12VIN
16 12VOUT
4 TIMER
2 VEEIN
15 VEEOUT
8 GND
+
CP4
+
-
-
-
+
+
-
-
-
+
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GATE 11 12VIN 5VOUT 50A 3VOUT
3VSENSE 3VIN 10 9
3VOUT 5VOUT 3 14
- +
- +
Q8 Q7
2.5V UVL CP3
REF
REF
5
LTC1643L/LTC1643H
APPLICATIONS INFORMATION
Hot Circuit Insertion When a circuit board is inserted into a live PCI slot, the supply bypass capacitors on the board can draw huge transient currents from the PCI power bus as they charge up. The transient currents can cause permanent damage to the connector pins and cause glitches on the power bus, causing other boards in the system to reset. The LTC1643 is designed to turn a board's supply voltages on and off in a controlled manner, allowing the board to be safely inserted or removed from a live PCI slot without glitching the system power supplies. The chip also protects the PCI supplies from shorts and monitors the supply voltages. The LTC1643H is designed for motherboard applications, while the LTC1643L is designed for CompactPCI applications where the chip resides on the plug-in board. LTC1643 FEATURE SUMMARY 1. Allows safe board insertion and removal from either a motherboard (LTC1643H) or CompactPCI board (LTC1643L). 2. Controls all four PCI supplies: -12V, 12V, 3.3V and 5V. 3. Programmable fold-back current limit: a programmable analog current limit with a value that depends on the output voltage. If the output is shorted to ground, the current limit drops to keep power dissipation and supply glitches to a minimum. 4. Programmable circuit breaker: if a supply remains in current limit too long, the circuit breaker will trip, the supplies will be turned off and the FAULT pin pulled low. 5. Current limit power-up: the supplies are allowed to power up in current limit. Allows the chip to power up boards with widely varying capacitive loads without tripping the circuit breaker. The maximum allowable power-up time is programmable using the TIMER pin. 6. -12V and 12V power switches on chip. 7. Power good output: monitors the voltage status of the four supply voltages. 8. Space saving 16-pin SSOP package. PCI Power Requirements PCI systems usually require four power rails: 5V, 3.3V, 12V and -12V. Systems implementing the 3.3V signaling environment are usually required to provide all four rails in every system. Systems implementing the 5V signaling environment may either ship the 3.3V supply with the system or provide a means to add it afterward. The tolerance of the supplies as measured at the components on the plug-in card is summarized in Table 1.
Table 1. PCI Power Supply Requirements
SUPPLY 5V 3.3V 12V - 12V TOLERANCE 5V 5% 3.3V 0.3V 12V 5% -12V 10% CAPACITIVE LOAD < 3000F < 3000F < 500F < 120F
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LTC1643L/LTC1643H
APPLICATIONS INFORMATION
Power-Up Sequence The power supplies are controlled by placing external N-channel pass transistors in the 3.3V and 5V power paths, and internal pass transistors for the 12V and -12V power paths (Figure 1). Resistors R1 and R2 provide current fault detection and R7 and C1 provide current control loop compensation. Resistors R5 and R6 prevent high frequency oscillations in Q1 and Q2. When the ON pin (Pin 5) is pulled high, the pass transistors are allowed to turn on and a 20A current source is connected to the TIMER pin (Pin 4) (Figure 2). The current in each pass transistor increases until it reaches the current limit for each supply. Each supply is then allowed to power up at the rate dv/dt = 50A/C1 or as determined by the current limit and the load capacitance whichever is slower. Current limit faults are ignored while the TIMER pin (Pin 4) voltage is ramping up and is less than 0.9V below 12VIN (Pin 1). Once all four supply voltages are within tolerance, the PWRGD pin (Pin 7) will pull low. Power-Down Sequence When the ON (Pin 5) is pulled low, a power-down sequence begins (Figure 3). Internal switches are connected to each of the output supply voltage pins to discharge the bypass capacitors to ground. The TIMER pin (Pin 4) is immediately pulled low. The GATE pin (Pin 11) is pulled down by a 200A current source to prevent the load currents on the 3.3V and 5V supplies from going to zero instantaneously and glitching the power supply voltages. When any of the output voltages dip below its threshold, the PWRGD pin (Pin 7) pulls high. Timer During a power-up sequence, a 20A current source is connected to the TIMER pin (Pin 4) and current limit faults are ignored until the voltage ramps to within 0.9V of 12VIN (Pin 1). This feature allows the chip to power up a PCI slot that can accept boards with widely varying capacitive loads on the supplies. The power-up time will be:
R2 0.005
SYSTEM POWER SUPPLY 9 3VIN GND 1 12VIN 2 VEEIN 5 ON 8 PCI POWER SYSTEM CONTROLLER RESET R3 10k R4 10k 6 10
3VSENSE GATE
FAULT TIMER
7
PWRGD
Figure 1. Typical Application
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R1 0.007
Q1 IRF7413
5V 5A
Q2 IRF7413
R6 10
3.3V 7.6A GND
R5 10 11 3 13 12 5VSENSE 14 5VOUT
R7 1k C1 0.047F
3VOUT 5VIN
12VOUT LTC1643H VEEOUT
16 15 4 C2 0.1F
12V 500mA -12V 100mA
LOGIC RESET
1643 TA01
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LTC1643L/LTC1643H
APPLICATIONS INFORMATION
ON 10V/DIV
TIMER 10V/DIV
GATE 10V/DIV
12VOUT 5V/DIV 5VOUT 5V/DIV 3VOUT 5V/DIV VEEOUT 5V/DIV
FAULT 10V/DIV PWRGD 10V/DIV
10ms/DIV
Figure 2. Normal Power-Up Sequence
C *V t ON 2 SUPPLY SUPPLY ILIMIT - ILOAD
For CSUPPLY = 2000F, VSUPPLY = 5V, ILIMIT = 7A, ILOAD = 5A, the turn-on time will be ~10ms. The timer period should be set longer than the maximum supply turn-on time but short enough to not exceed the maximum safe operating area of the pass transistor during a short circuit. The timer period will be:
* 11.1V C tTIMER = TIMER 22A For CTIMER = 0.1F, the timer period will be ~ 50ms. The TIMER pin (Pin 4) is immediately pulled low when ON (Pin 5) goes low.
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ON 10V/DIV
TIMER 10V/DIV
GATE 10V/DIV
12VOUT 5V/DIV 5VOUT 5V/DIV 3VOUT 5V/DIV
VEEOUT 5V/DIV
FAULT 10V/DIV PWRGD 10V/DIV
1643 F02
10ms/DIV
1643 F03
Figure 3. Normal Power-Down Sequence
Thermal Shutdown The internal switches for the 12V and -12V supplies are protected by an internal current limit and thermal shutdown circuit. When the temperature of chip reaches 150C, all switches will be latched off and the FAULT pin (Pin 6) will be pulled low. Short-Circuit Protection During a normal power-up sequence, if the TIMER (Pin 4) is done ramping and a supply is still in current limit, all of the pass transistors will be immediately turned off and the FAULT pin (Pin 6) will be pulled low as shown in Figure 4. If a short circuit occurs after the supplies are powered up, the shorted supply's current will drop immediately to the limit value (Figure 5).
LTC1643L/LTC1643H
APPLICATIONS INFORMATION
ON 10V/DIV
TIMER 10V/DIV
GATE 10V/DIV
12VOUT 5V/DIV 3VOUT 5V/DIV 5VOUT 5V/DIV VEEOUT 5V/DIV
FAULT 10V/DIV PWRGD 10V/DIV
20ms/DIV
Figure 4. Power-Up into a Short on 3.3V Output
If the supply remains in current limit for more than 15s, all of the supplies will be latched off. The 15s delay prevents quick current spikes--for example, from a fan turning on--from causing false trips of the circuit breaker. The chip will stay in the latched-off state until ON (Pin 5) is cycled low then high, or the 12VIN pin (Pin 1) power supply is cycled. To prevent excessive power dissipation in the pass transistors and to prevent voltage spikes on the supplies during short-circuit conditions, the current limit on each supply is designed to be a function of the output voltage. As the output voltage drops, the current limit decreases. Unlike a traditional circuit breaker function where huge currents can flow before the breaker trips, the current foldback feature assures that the supply current will be kept at
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ON 10V/DIV
TIMER 10V/DIV
GATE 10V/DIV
12VOUT 5V/DIV 5VOUT 5V/DIV 3VOUT 5V/DIV
VEEOUT 5V/DIV
FAULT 10V/DIV PWRGD 10V/DIV
1643 F04
20ms/DIV
1643 F05
Figure 5. Short Circuit on 5V
a safe level and prevent voltage glitches when powering up into a short. The current limit for the 5V and 3.3V supplies is set by placing a sense resistor between 5VIN (Pin 13) and 5VSENSE (Pin 12) and between 3VIN (Pin 9) and 3VSENSE (Pin 10). The current limit will be set by: ILIMIT = 53mV/RSENSE For a 0.005 resistor, the current limit will be set at 10.6A and fold back to 1.5A when the output is shorted. For a 0.007 resistor, the current limit will be set at 7.6A and fold back to 1.1A when the output is shorted. The current for the internal 12V switch is set at 850mA folding back to 250mA and the -12V switch at 450mA folding back to 160mA.
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LTC1643L/LTC1643H
APPLICATIONS INFORMATION
CompactPCI Application The LTC1643L is ideal for hot swapping CompactPCI boards. The typical application is shown in Figure 6. Because the turn-on signal is active low for CompactPCI, the LTC1643L must be used. Capacitors C3 and C4 are required when hot-plugging the chip into a live backplane. Systems Without 3.3V If a system does not use a 3.3V supply, the LTC1643 should be connected as shown in Figure 7. Increasing 12V and - 12V Current Capability The internal switches in the LTC1643 are designed for up to 500mA loads on 12V and 200mA on - 12V. If more current is needed, then the circuits in Figure 8 can be used. For the 12V supply, P-channel transistor Q4 is placed in parallel with the internal switch. When the LTC1643H is turned off, the GATE pin is held low and transistor Q3 is turned on which pulls the gate of Q4 high, turning it off. When the LTC1643H is turned on, the GATE pin goes high, turning off Q3 and allowing R8 to pull the gate of Q4 low to turn it on. Because Q4 is in parallel with the internal 12V switch, the load current will be shared in proportion to their respective RDS(ON) values. For example, if the RDS(ON) of the external switch is 0.2 and the internal switch is 0.4, then, at 1.5A load current, the external switch will provide 1A and the internal switch 500mA. The circuit breaker current will be reached when the internal current reaches 1A and the external current is 2A or 3A load current. For the -12V supply, N-channel transistor Q6 is used to provide the extra load current. When the LTC1643H is turned on, the internal VEE switch is turned on and the -12V output starts to pull down through D1 and turns on Q5. When Q5 turns on, the gate of Q6 starts to rise, turning it on. When the LTC1643H turns off, the VEEOUT pin is pulled up to ground, diode D1 is reversed biased, and transistor Q5 turns off, which allows resistor R10 to turn off Q6. The internal -12V switch provides the current limit for the supply, but because the high RDS(ON) of the internal switch (1.2) is in series with D1, very large currents can flow through Q6 before the circuit breaker trips. However, if a short to ground occurs on the -12V output, diode D1 will prevent Q5 from turning on, which will prevent Q6 from turning on.
R1 0.007 5V R2 0.005 3.3V VID CompactPCI CONNECTOR R8 10k 5 VID R11 10k HEALTHY# 12V -12V GND C3 0.1F C4 0.1F R5 10 9 3VIN ON 8 12VOUT 6 7 LTC1643L FAULT VEEOUT TIMER GND 8 16 15 4 C2 0.1F
1643 F06
BD_SEL#
R3 10k
PWRGD 1 12VIN 2 VEEIN
Figure 6. Typical CompactPCI Application
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Q1 IRF7413
5V 5A 3.3V 7.6A
Q2 IRF7413 R6 10
R7 1k 14 C1 0.047F
10
11
3
13
12 5VSENSE
3VSENSE GATE
3VOUT 5VIN
5VOUT
12V 500mA -12V 100mA
LTC1643L/LTC1643H
APPLICATIONS INFORMATION
R1 0.007 Q1 IRF7413 5V 5A GND R6 10 SYSTEM POWER SUPPLY 9 8 GND 1 12VIN 2 VEEIN 5 ON PCI POWER SYSTEM CONTROLLER R3 10k R4 10k 6 3VIN 13 5VIN 10 12 11 3 14 3VSENSE 5VSENSE GATE 3VOUT 5VOUT R7 1k C1 0.047F
FAULT TIMER
7
PWRGD
Figure 7. System Without 3.3V Supply
Q4 Si9400 Q3 TP0610T R8 100k C3 0.1F Q1 IRF7413 R1 0.007
SYSTEM POWER SUPPLY
R2 0.005
Q2 IRF7413
1 8 2 5 R3 10k R4 10k GND VEEIN ON
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12VIN 3VIN
3VSENSE GATE 3VOUT
PCI POWER SYSTEM CONTROLLER
6
FAULT
7
PWRGD
Figure 8. Increasing 12V and - 12V Current Capability
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12VOUT LTC1643H VEEOUT
16 15 4 C2 0.1F
12V 500mA -12V 100mA
1643 F07
12V 1.5A
5V 5A
R6 10 R5 10 11 3 13 5VIN 12 16 R7 1k C1 0.047F
3.3V 7.6A GND
5VSENSE 12VOUT Q5 TP0610T
LTC1643H
VEEOUT
15 R9 200 D1 1N4148
TIMER
4 C2 0.1F R10 200 Q6 Si9410DY -12V 1.5A
1643 F08
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LTC1643L/LTC1643H
PACKAGE DESCRIPTION U
Dimensions in inched (millimeters) unless otherwise noted.
GN Package 16-Lead Plastic SSOP (Narrow 0.150)
(LTC DWG # 05-08-1641)
0.189 - 0.196* (4.801 - 4.978) 16 15 14 13 12 11 10 9
0.229 - 0.244 (5.817 - 6.198)
0.150 - 0.157** (3.810 - 3.988)
1 0.015 0.004 x 45 (0.38 0.10) 0.007 - 0.0098 (0.178 - 0.249) 0.016 - 0.050 (0.406 - 1.270) * DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE ** DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE 0 - 8 TYP 0.053 - 0.068 (1.351 - 1.727)
23
4
56
7
8 0.004 - 0.0098 (0.102 - 0.249)
0.008 - 0.012 (0.203 - 0.305)
0.025 (0.635) BSC
GN16 (SSOP) 1197
RELATED PARTS
PART NUMBER LTC1421 LTC1422 LT1640 DESCRIPTION Hot Swap Controller Hot Swap Controller - 48V Hot Swap Controller COMMENTS Multiple Supply Single Supply Negative High Voltage Supplies
12
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408)432-1900 q FAX: (408) 434-0507 q www.linear-tech.com
1643i LT/TP 0998 4K * PRINTED IN USA
(c) LINEAR TECHNOLOGY CORPORATION 1998

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