LTC4352

7

4352f

OPERATION

The LTC4352 controls either single or back-to-back

N-channel MOSFETs in order to emulate an ideal diode. Dual

MOSFETs eliminate current flow from the input to the output

in an input undervoltage or overvoltage condition.

When enabled, an amplifier (AMP) monitors the voltage

The amplifier controls the gate of the external MOSFET

The gate voltage rises to enhance the MOSFET if the load

current causes more than 25mV of drop. For large output

currents the MOSFET gate is driven fully on and the voltage

In the case of an input supply short-circuit, when the

MOSFET is conducting, a large reverse current starts

flowing from the load towards the input. The AMP detects

this failure condition as soon as it appears, and turns off

the MOSFET by pulling down the GATE pin. The REV pin

can be used to allow reverse current, overriding the diode

behavior.

The AMP quickly pulls-up the GATE pin whenever it senses

a large forward voltage drop. An external capacitor between

the CPO and SOURCE pins is needed for fast gate pull-up.

This capacitor is charged up, at device power-up, by the

internal charge-pump. This stored charge is used for the

fast gate pull-up.

The GATE pin sources current from the CPO pin, and sinks

current to the SOURCE and GND pins. Internal clamps

limit the GATE to SOURCE voltage to 6.1V, and the CPO

to SOURCE voltage to 6.7V. The same clamps also limit

the CPO and GATE pins to a diode voltage below the

SOURCE pin.

passage. The MOSFET is held off whenever the OV pin

below 2.57V. There is a 40μs delay from all three condi-

tions becoming good to GATE being allowed to turn on.

Overvoltage causes a fast turn-off, while undervoltage

activates a 100μA pull-down on GATE after a 7μs delay.

Open-drain pull-down, M1, pulls the STATUS pin low

when the GATE to SOURCE voltage exceeds 0.7V, to

indicate that power is passing through the MOSFET. The

FAULT output, M2, pulls low during an undervoltage or

overvoltage fault condition. It also pulls low when GATE

is fully on and the forward voltage drop exceeds 250mV,

indicating the MOSFET has too much current or has failed

open circuit.

LDO is a low dropout regulator that generates a 4.1V

below 2.9V is being ORed, an external supply in the 2.9V