LTC4232 datasheet(7/20 Pages) LINER

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LTC4234

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PIN FUNCTIONS

DNC: Do Not Connect. Leave open.

FB: Foldback and Power Good Input. Connect this pin to

an external resistive divider from OUT. If the voltage falls

below 0.6V, the current limit is reduced using a foldback

profile (see the Typical Performance Characteristics sec-

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

low to indicate the power is bad

FLT: Overcurrent Fault Indicator. Open-drain output pulls

low when an overcurrent fault has occurred and the circuit

breaker trips. For overcurrent auto-retry tie to UV pin (see

Applications Information section for details).

GATE: 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. Dur-

ing 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.

GND: Device Ground.

IMON: Current Monitor Output. The current in the internal

MOSFET switch is divided by 200,000 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 20A.

INTVCC: Internal 3.1V Supply Decoupling Output. This pin

must have a 1.0µF or larger bypass capacitor. Overloading

this pin can disrupt internal operation.

ISET: Current Limit Adjustment Pin. For 22.5A 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 is

made proportional to temperature of the MOSFET switch.

OUT: Output of Internal MOSFET Switch. Connect this pin

directly to the load.

OV: 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.

PG: 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.

SENSE: Current Sense Node and MOSFET Drain. One

exposed pad on the UH 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. Connect the SENSE pin 31 to the SENSE– pin 34.

SENSE−: Current Limit and Current Monitor Amplifier

Input. The current limit circuit controls the GATE pin to

limit the voltage between the VDD and SENSE– pins to

15mV (22.5A) or less depending on the voltage at the FB

pin. This pin must be connected to SENSE pin on the right

side (connect Pin 34 to Pin 31).

TIMER: 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 2ms overcurrent

delay and 900ms cool down time.

UV: Undervoltage Comparator Input. Tie high to INTVCC

if unused. Connect this pin to an external resistive divider

from VDD. If the UV pin voltage falls below 1.15V, an un-

dervoltage 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 this pin to the FLT pin.

VDD: Supply Voltage and Current Sense Input. This ex-

posed pad must be soldered to input power. VDD has an

undervoltage lockout threshold of 2.73V.

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