LTC4368
7
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 V
OUT
falls 100mV below V
IN
, 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 V
OUT
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.