LTC4232 datasheet(7/18 Pages) AD

7 / 18 page

LT4200

Rev. 0

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PIN FUNCTIONS

UV (Pin 1): Undervoltage Comparator Input. Connect this

pin to an external resistive divider from VDD. If the UV pin

voltage falls below 1.15V, an undervoltage is detected

and the switch turns off. Pulling this pin below 0.62V

resets the overcurrent fault and allows the switch to turn

back on (see Application Information section for details).

If overcurrent auto-retry is desired, then tie UV to the FLT#

pin. Tie UV to INTVCC if unused.

OV (Pin 2): Overvoltage Comparator Input. Connect this

pin to an external resistive divider from VDD. If the voltage

at this pin rises above 1.235V, an overvoltage is detected,

and the switch turns off. Tie to GND if unused.

IMON (Pin 3): Current Monitor Output. The current in

the internal MOSFET switch is divided by 500,000 and

sourced from this pin. Placing a 20k resistor on this pin

allows a 0V to 2V voltage swing when current ranges

from 0A to 50A.

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

capacitor between this pin and ground to set a 12ms/µF

duration for current limit before the switch is turned off. If

the UV pin is toggled low while the MOSFET switch is off,

the switch will turn on again following cool down time of

4.14s/µF duration. Tie this pin to INTVCC for a fixed 0.5ms

overcurrent delay and 900ms cool down time.

INTVCC (Pin 5): Internal 3.1V Supply Decoupling Output.

This pin must have a 1µF or larger bypass capacitor.

Overloading this pin can disrupt internal operation.

GATE (Pin 6): Gate Drive for Internal N-Channel MOSFET.

An internal 24µA current source charges the gate of the

N-channel MOSFET. At start-up, the GATE pin ramps up at

a 0.35V/ms rate determined by internal circuitry. During

an undervoltage or overvoltage condition, a 250µA pull-

down current turns the MOSFET off. During a short-circuit

or undervoltage lockout condition, a 140mA pull-down

current source between GATE and OUT is activated.

OUT (Pins 7–21): Output of Internal MOSFET Switch.

Connect this pin directly to the load.

VDD (Pins 22–30): Supply Voltage and Current Sense

Input. These pins must be soldered to input power. VDD

has an undervoltage lockout threshold of 2.73V.

GND (Pin 31): Device Ground.

SENSE– (Pin 32): Current Sense Node and MOSFET Drain.

The exposed pad on the UHG package is connected to

SENSE– and should be soldered to an electrically isolated

printed circuit board trace to properly transfer the heat

out of the package.

SENSE+ (Pin 32): Current Limit and Current Monitor

Amplifier Input. The current limit circuit controls the GATE

pin to limit the voltage between the SENSE+ and SENSE–

pin to 17mV (57A) or less depending on the voltage at

the FB pin and ISET. This pin must be connected to VDD

pin (connect Pin 32 to Pin 26).

PG (Pin 33): Power Good Indicator. Open-drain output

pulls low when the FB pin drops below 1.21V indicating

the power is bad. If the voltage at FB rises above 1.235V

and the GATE-to-OUT voltage exceeds 4.2V, the open-

drain pull-down releases the PG pin to go high.

FLT# (Pin 34): Overcurrent Fault Indicator. Open-drain

output pulls low when an overcurrent fault has occurred

and the circuit breaker trips. For overcurrent auto-retry

tie FLT# to UV pin (see Applications Information section

for details).

FB (Pin 35): Foldback and Power Good Input. Connect this

pin to an external resistive divider from OUT. If the voltage

falls below 0.9V, the current limit is reduced using a fold-

back profile (see the Typical Performance Characteristics

section). If the voltage falls below 1.21V, the PG pin will

pull low to indicate the power is bad.

ISET (Pin 36): Current Limit Adjustment Pin. For 57A

current limit value, open this pin. This pin is driven by

a 20k resistor in series with a voltage source. The pin

voltage is used to generate the current limit threshold.

The internal 20k resistor (RISET) and an external resistor

(RSET) between ISET and ground create an attenuator that

lowers the current limit value. Due to circuit tolerance

RSET should not be less than 2k. In order to match the

temperature variation of the sense resistor, the voltage on

this pin increases at the same rate as the sense resistance

increases. Therefore the voltage at ISET pin is made pro-

portional to temperature of the MOSFET switch.

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