LTC1421 datasheet(6/24 Pages) LINER

6 / 24 page

LTC1421/LTC1421-2.5

PIN FUNCTIONS

RAMP (Pin 10): Analog Power-Up Ramp Control Pin. By

connecting an external capacitor between the RAMP and

GATEHI, a positive linear voltage ramp on GATEHI and

GATELO is generated on power-up with a slope equal to

µA/CRAMP.

FB (Pin 11): Analog Feedback Input. FB is used to set the

reset threshold voltage on VCCLO. For a 5V supply leave FB

floating. For a 3.3V supply, short FB to VCCLO.

GND (Pin 12): Ground

COMP + (Pin 13): Noninverting Comparator Input.

COMP– (Pin 14): Inverting Comparator Input.

COMPOUT (Pin 15): Open Drain Comparator Output.

VOUTHI(Pin 16): High Supply Voltage Output. This must be

the higher of the two supply voltage outputs.

GATEHI (Pin 17): The High Side Gate Drive for the High

Supply N-Channel. An internal charge pump guarantees at

least 6V of gate drive. The slope of the voltage rise at

GATEHI is set by the external capacitor connected between

GATEHI and RAMP. When the circuit breaker trips, GATEHI

is immediately pulled to GND.

SETHI (Pin 18): The Circuit Breaker Set Pin for the High

Supply. With a sense resistor placed in the supply path

between VCCHI and SETHI, the circuit breaker will trip when

the voltage across the resistor exceeds 50mV for more

than 20

µs. To disable the circuit breaker, VCCHI and SETHI

should be shorted together.

VCCHI (Pin 19): The Positive Supply Input. This must be the

higher of the two input supply voltages. An undervoltage

lockout circuit disables the chip until the voltage at VCCHI

is greater than 2.45V.

VOUTLO(Pin 20): Low Supply Voltage Output. This must be

the lower of the two supply voltage outputs.

GATELO (Pin 21): The High Side Gate Drive for the Low

Supply N-Channel Pass Transistor. An internal charge

pump guarantees at least 10V of gate drive. The slope of

the voltage rise at GATELO is set by the external capacitor

connected between GATEHI and RAMP. When the circuit

breaker trips GATELO is immediately pulled to GND.

SETLO (Pin 22): The Circuit Breaker Set Pin for the Low

Supply. With a sense resistor placed in the supply path

between VCCLO and SETLO, the circuit breaker will trip

when the voltage across the resistor exceeds 50mV for

more than 20

µs. To disable the circuit breaker, VCCLO and

SETLO should be shorted together.

VCCLO (Pin 23): The Positive Supply Input. VCCLO must be

equal to or lower voltage than VCCHI. An undervoltage

lockout circuit disables the chip until the voltage at VCCLO

is greater than 2.45V.

AUXVCC (Pin 24): The supply input for the GATELO and

GATEHI discharge circuitry. Connect a 1

µF capacitor to

ground. AUXVCC is powered from VCCLO via an internal

Schottky diode and series resistor.

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