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LT4363

4363fa

PIN FUNCTIONS

ENOUT:OpenCollectorEnableOutput.TheENOUTpingoes

high impedance when the voltage at the OUT pin is within

0.5V of VCC and 3V above GND, indicating the external

MOSFET is fully on. The state of the pin is latched until the

OUT pin voltage drops below 2V, resetting the latch. The

internal NPN is capable of sinking up to 2mA of current.

Exposed Pad (DFN Package Only): Exposed pad may be

left open or connected to device ground (GND).

FB: Voltage Regulator Feedback Input. Connect this pin to

the center tap of the resistive divider connected between

the OUT pin and ground. During an overvoltage condition,

the GATE pin is controlled to maintain a 1.275V threshold

at the FB pin. Connect to GND to disable the OV clamp.

FLT: Open Collector Fault Output. This pin pulls low after

the voltage at the TMR pin has reached the fault threshold

of1.275V.Itindicatesthepasstransistorisabouttoturnoff

becauseeitherthesupplyvoltagehasstayedatanelevated

level for an extended period of time (voltage fault) or the

device is in an overcurrent condition (current fault). The

internal NPN is capable of sinking up to 2mA of current.

GATE:N-ChannelMOSFETGateDriveOutput.TheGATEpin

is pulled up by an internal charge pump current source and

clamped to 14V above the OUT pin. Both voltage and cur-

rent amplifiers control the GATE pin to regulate the output

voltage and limit the current through the MOSFET.

GND: Device Ground.

OUT: Output Voltage Sense Input. This pin senses the

voltage at the source of the external N-channel MOSFET.

The voltage difference between VCC and OUT sets the fault

timer current. When this difference drops below 0.5V, the

EN pin goes high impedance.

OV (LT4363-2): Overvoltage Comparator Input. When OV

is above its threshold of 1.275V, the fault retry function

is inhibited even when the TMR pin voltage has reached

its retry threshold. As soon as the voltage at OV pin falls

below its lower threshold the GATE pin is allowed to turn

back on. Connect to GND if unused.

SHDN: Shutdown Control Input. The LT4363 can be

shutdown to a low current mode by pulling the SHDN pin

below the threshold of 0.4V. Pull this pin above 2.1V or

disconnect it to allow the internal current source to turn

the part back on. The leakage current to ground at the pin

should be limited to no more than 1µA if no external pull

up is used to turn the part on. The SHDN pin can be pulled

up to 100V or below GND by 60V without damage.

SNS: Current Sense Input. Connect this pin to the input of

thecurrentsenseresistor.Thecurrentlimitcircuitcontrols

the GATE pin to limit the sense voltage between SNS and

OUT pins to 50mV. This is reduced to 25mV in a severe

fault when OUT is below 2V. When in current limit mode,

a current source charges up the TMR pin. The voltage

difference with the OUT pin must be limited to less than

30V. Connect to OUT pin if unused.

TMR: Fault Timer Input. Connect a capacitor between this

pin and ground to set the times for early fault warning,

fault turn-off, and cool down periods. The current charg-

ing up this pin during fault conditions depends on the

voltage difference between the VCC and OUT pins. When

TMR reaches 1.275V, the FLT pin pulls low to indicate the

detection of a fault condition. If the condition persists, the

pass transistor turns off when TMR reaches the threshold

of 1.375V. A 2µA current source then continues to pull

the TMR up. When TMR reaches 4.3V, the 2µA current

reverses direction and starts to pull the TMR pin low.

When TMR reaches the retry threshold of 0.5V, the GATE

pin pulls high turning back on the pass transistor for the

LT4363-2 version. The GATE pin latches low after fault

time out for the LT4363-1.

UV: Undervoltage Comparator Input. When UV falls below

its threshold of 1.275V, the GATE is pulled down with a

1mA current. When UV rises above 1.275V plus the hys-

teresis, the pull down current disappears and the GATE

pin is pulled up by the internal charge pump. If unused,

connect to VCC.

VCC: Positive Supply Voltage Input. The positive supply

input ranges from 4V to 80V for normal operation. It can

also be pulled below ground by up to 60V during a reverse

battery condition, without damaging the part. Shutting

down the LT4363 by pulling the SHDN pin to ground will

reduce the supply current to 7µA.

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