LTC4359 datasheet(6/20 Pages) LINER

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LTC4359

Rev D

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BLOCK DIAGRAM

OPERATION

The LTC4359 controls an external N-channel MOSFET to

form an ideal diode. The GATE amplifier (see Block Dia-

gram) senses across IN and OUT and drives the gate of the

MOSFET to regulate the forward voltage to 30mV. As the

load current increases, GATE is driven higher until a point

is reached where the MOSFET is fully on. Further increases

in load current result in a forward drop of RDS(ON)• ILOAD.

If the load current is reduced, the GATE amplifier drives

the MOSFET gate lower to maintain a 30mV drop. If the

input voltage is reduced to a point where a forward drop

of 30mV cannot be supported, the GATE amplifier drives

the MOSFET off.

In the event of a rapid drop in input voltage, such as an

input short-circuit fault or negative-going voltage spike,

reverse current temporarily flows through the MOSFET.

This current is provided by any load capacitance and by

other supplies or batteries that feed the output in diode-

OR applications.

4359 BD

CHARGE PUMP

TYP. 500kHz

SHUTDOWN

–

FPD

COMP

GATE

AMP

30mV

2.6µA

SOURCE

SHDN

GATE

–1.7V

OUT

VOUT

VIN

VSS

+–

–

NEGATIVE

COMP

The FPD COMP (Fast Pull-Down Comparator) quickly

responds to this condition by turning the MOSFET off in

300ns, thus minimizing the disturbance to the output bus.

The IN, SOURCE, GATE and SHDN pins are protected

againstreverseinputsofupto–40V.TheNEGATIVECOMP

detects negative input potentials at the SOURCE pin and

quickly pulls GATE to SOURCE, turning off the MOSFET

and isolating the load from the negative input.

When pulled low the SHDN pin turns off most of the

internal circuitry, reducing the quiescent current to 9µA

and holding the MOSFET off. The SHDN pin may be either

driven high or left open to enable the LTC4359. If left

open, an internal 2.6µA current source pulls SHDN high.

In applications where Q1 is replaced with back-to-back

MOSFETs, the SHDN pin serves as an on/off control for

the forward path, as well as enabling the diode function.

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