LT1913 datasheet(7/22 Pages) AD

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LTC4368

Rev. B

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PIN FUNCTIONS

Exposed Pad: The exposed pad may be left open or con-

nected to device ground.

FAULT: Fault Indication Output. Connect to a pull-up resis-

tor. This high voltage open drain output is pulled low if

there is a voltage or current fault, if SHDN is low, or if

VIN has not risen above VIN(UVLO). Leave unconnected if

unused.

GATE: Gate Drive Output for External N-channel MOSFETs.

An internal charge pump provides 35µA of pull-up current

and up to 13.1V of enhancement to the gate of an external

MOSFET. When turned off, GATE is pulled just below the

lower of VIN or VOUT. When VIN goes negative, GATE is

automatically connected to VIN.

GND: Device Ground.

OV: Overvoltage Comparator Input. Connect this pin to an

external resistive divider to set the desired VIN overvolt-

age fault threshold. This input connects an accurate, fast

(1µs) comparator with a 0.5V rising threshold and 25mV

of hysteresis. When OV rises above its threshold, a 60mA

current sink pulls down on the GATE output. When OV

falls back below 0.475V, and after a 32ms GATE turn-on

delay waiting period, the GATE charge pump is enabled.

The low leakage current on this input allows the use of

large valued resistors for the external resistive divider.

Connect to GND if unused.

RETRY: Retry or Latch-Off Selection Input. Connect to

ground to latch off the MOSFETs after a forward over-

current fault. To turn the external MOSFETs back on, the

SHDN pin must be toggled low then high. Connect RETRY

to an external capacitor to configure a 5.5ms/nF delay

before the MOSFETs automatically turn on again. Leave

unconnected if unused.

SENSE: Overcurrent Sense Input. Connect a current

sense resistor between SENSE and VOUT. This input

detects overcurrent faults in both directions: forward

at ΔVSENSE = 50mV, and reverse at ΔVSENSE = –50mV

(LTC4368-1 option) or ΔVSENSE = –3mV (LTC4368-2

option). When an overcurrent fault is detected, a 60mA

current sink pulls down on the GATE output, thus quickly

disconnecting the load from the input. After a reverse cur-

rent fault, when VOUT falls 100mV below VIN, the LTC4368

automatically turns on the external MOSFETs. A forward

overcurrent fault uses the RETRY pin to set the conditions

for reconnecting power to the load. Connect to VOUT if

unused.

SHDN: Shutdown Control Input. Assuming no voltage or

current faults, SHDN high enables the GATE charge pump

which in turn enhances the gate of the external N-channel

MOSFETs. A low on SHDN generates a pull down on the

GATE output with a 90µA current sink and places the

LTC4368 in low current mode (5µA). If a forward overcur-

rent condition latches off the external MOSFETs (RETRY

grounded), the SHDN pin must be toggled low then high

to re-enable the charge pump that enhances the external

MOSFETs. If VIN goes above 80V, the SHDN pin voltage

must be kept below 80V.

UV: Undervoltage Comparator Input. Connect this pin to

an external resistive divider to set the desired VIN under-

voltage fault threshold. This input connects to an accu-

rate, fast (1µs) comparator with a 0.5V falling threshold

and 25mV of hysteresis. When UV falls below its thresh-

old, a 60mA current sink pulls down on the GATE output.

When UV rises back above 0.525V, and after a 32ms GATE

turn-on delay waiting period, the GATE charge pump is

enabled. The low leakage current on this input allows the

use of large valued resistors for the external resistive

divider. If unused and VIN is less than 80V, connect to

VIN with a 510k resistor.

VIN: Power Supply Input. Maximum protection range:

–40V to 100V. Operating range: 2.5V to 60V. This pin

can be hot swapped and has a 2.2V UVLO.

VOUT: Output Voltage Sense Input. Connect a current

sense resistor between VOUT and SENSE. The GATE

charge pump voltage is referenced to VOUT. It is used as

the charge pump input when VOUT is greater than approxi-

mately 5V. The reverse current fault comparators require

that VOUT rise above its 2.2V UVLO. VOUT cannot be hot

swapped with supplies above 24V. Place at least 1µF from

VOUT to GND.

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