LTC4241

7

sn4241 4241f

primary controller internal circuitry. A 0.5

Ω switch is

current limit. An undervoltage lockout circuit prevents the

less than 9V.

current limit.

3.3V output supply voltage. The PWRGD signal cannot go

TIMER (Pin 4): Current Limit Fault Timer Input. Connect a

capacitor from TIMER to ground. With the primary con-

troller turned off (ON = GND) or the internal circuit breaker

tripped due to a PCI supply fault (FAULT = low), the TIMER

pin is internally held at ground. When the primary control-

ler is turned on, a 22

µA pull-up current source is con-

nected to TIMER. Current limit faults from the PCI supplies

will be ignored until the voltage at the TIMER pin rises to

ON (Pin 5): On Control Input. A rising edge turns on the

external N-channel FETs for 3.3V and 5V PCI supplies, the

internal 12V and –12V switches and a falling edge turns it

off. If the ON pin is cycled low then high following the trip

of the circuit breaker due to a PCI supply fault, the circuit

breaker is reset.

FAULT (Pin 6): Fault Output. Open drain logic output used

by both the primary and auxiliary controller to indicate an

overcurrent fault condition. When any of the PCI and 3.3V

auxiliary supplies are in current limit fault, the controller

detecting the fault (primary or auxiliary) will be latched off

and the FAULT pin will be pulled low. Current limit faults

from the PCI supplies are ignored while the voltage at the

fault detected by the primary controller will not cause the

auxiliary controller to latch off and vice versa.

PWRGD (Pin 7): Power Good Output. Open drain logic

output used by the primary controller to indicate the

voltage status of the PCI supplies. PWRGD remains low

PI FU CTIO S

power good threshold voltage, PWRGD will go high after

a 15

µsdeglitchingtime.Theswitcheswillnotbeturnedoff

when PWRGD goes high.

GND (Pin 8): Chip Ground

AUXGATE (Pin 9): High Side Gate Drive for the 3.3V

Auxiliary External N-channel MOSFET. An internal charge

pump generates at least 8V of gate drive from a 3.3V

auxiliary supply. A zener clamps AUXGATE approximately

12V above the supply voltage at AUXIN. The rise time at

AUXGATE is set by an external AUXGATE capacitor con-

nected to ground and an internal 10

µA current source

provided by the charge pump. If the circuit breaker trips or

the auxiliary supply voltage hits the undervoltage lockout

threshold, a 50mA current sink rapidly pulls AUXGATE

low.

AUXSENSE (Pin 10): 3.3V Auxiliary Circuit Breaker Cur-

rent Sense Input. The load current is monitored by a sense

resistor connected between AUXIN and AUXSENSE. The

circuit breaker trips if the voltage across the sense resistor

exceeds 50mV and the AUXGATE pin voltage will be turned

off.

AUXIN (Pin 11): 3.3V Auxiliary Supply Input. This pin

powers the auxiliary controller internal circuitry. An

undervoltage lockout circuit disables the AUXGATE pin

until the supply voltage at AUXIN is greater than 2.6V.

AUXGATE is held at ground potential until the undervoltage

lockout deactivates. If no 3.3V auxiliary supply is available,

tie AUXIN to ground.

AUXON (Pin 12): ON Control Input for Auxiliary Supply. A

rising edge turns on the external N-channel FET for 3.3V

auxiliary supply and a falling edge turns it off. If the AUXON

pin is cycled low then high following the trip of the circuit

breaker due to a 3.3V auxiliary supply fault, the circuit

breaker is reset.

lockout circuit prevents the switches from turning on