5

LT4250L/LT4250H

4250lhf

OV (Pin 2): Analog Overvoltage Input. When OV is pulled

above the 1.255V threshold, an overvoltage condition is

detected and the GATE pin will be immediately pulled low.

The GATE pin will remain low until OV drops below the

1.235V threshold.

UV (Pin 3): Analog Undervoltage Input. When UV is

pulled below the 1.125V threshold, an undervoltage

condition is detected and the GATE pin will be immedi-

ately pulled low. The GATE pin will remain low until UV

rises above the 1.255 threshold.

The UV pin is also used to reset the electronic circuit

breaker. If the UV pin is cycled low and high following the

trip of the circuit breaker, the circuit breaker is reset and

a normal power-up sequence will occur. The response

time for this pin is 1.5

µs. Add an external capacitor to this

pin for additional filtering.

the lower potential of the power supply.

SENSE (Pin 5): Circuit Breaker Sense Pin. With a sense

SENSE, the overcurrent condition will pull down the

GATE pin and regulate the voltage across the resistor to

be 50mV. If the overcurrent condition exists for more

than 500

µs the electronic circuit breaker will trip and turn

off the external MOSFET.

If the current limit value is set to twice the normal

operating current, only 25mV is dropped across the

sense resistor during normal operation. To disable the

together.

GATE (Pin 6): Gate Drive Output for the External

N-Channel MOSFET. The GATE pin will go high when the

following start-up conditions are met: the UV pin is high,

45

µA current source and pulled low with a 50mA current

source. During current limit the GATE pin is pulled low

using a 100mA current source.

DRAIN (Pin 7): Analog Drain Sense Input. Connect this

pin to the drain of the external N-channel MOSFET and the

the switch is on.

pin to the higher potential of the power supply inputs and

BLOCK DIAGRA

–

+

+

–

+

–

DRAIN

4250 BD

GATE

SENSE

OUTPUT

DRIVE

PWRGD/PWRGD

50mV

REF

REF

UV

OV

LOGIC

REFERENCE

GENERATOR

–

+

+

–

500

µs

DELAY

GATE

DRIVER

UVLO