LTC2913 datasheet(15/24 Pages) AD

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LT4356-3

Rev D

For more information www.analog.com

APPLICATIONS INFORMATION

Shutdown

The LT4356-3 can be shut down to a low current mode

whenthevoltageattheSHDNpingoesbelowtheshutdown

threshold of 0.4V. The quiescent current drops to 7µA. All

functions are turned off including the auxiliary amplifier.

After the GATE pin pulls low due to a fault time out, the

LT4356-3 latches off. Allow sufficient time for the TMR

pin to discharge to 0.5V (typical discharge current is

2.2µA) and for the MOSFET to cool before attempting to

reset the part. To reset, pull the SHDN pin low for at least

100µs, then pull high with a slew rate of at least 10V/ms.

The SHDN pin can be pulled up to VCC or below GND by

up to 60V without damaging the pin. Leaving the pin open

allows an internal current source to pull it up and turn

on the part while clamping the pin to 2.5V. The leakage

current at the pin should be limited to no more than 1µA

if no pull up device is used to help turn it on.

Supply Transient Protection

The LT4356-3 is 100% tested and guaranteed to be safe

fromdamagewithsupplyvoltagesupto80V.Nevertheless,

voltagetransientsabove100Vmaycausepermanentdam-

age. During a short-circuit condition, the large change in

currentflowingthroughpowersupplytracesandassociated

wiring can cause inductive voltage transients which could

exceed100V.Tominimizethevoltagetransients,thepower

trace parasitic inductance should be minimized by using

wide traces. A small surge suppressor, D2, in Figure 9,

at the input will clamp the voltage spikes.

A total bulk capacitance of at least 22µF low ESR is re-

quired close to the source pin of MOSFET Q1. In addition,

the bulk capacitance should be at least 10 times larger

than the total ceramic bypassing capacitor on the input

of the DC/DC converter.

Figure 8. Overvoltage Regulator with P-Channel MOSFET

Reverse Input Protection

CTMR

0.1µF

RSNS

10m

IRLR2908

Si4435

VIN

12V

VOUT

12V, 3A

CLAMPED

AT 16V

43563 F08

LT4356DE-3

GND

TMR

OUT

SNS

SHDN

AOUT

IN+

VCC

FLT

4.99k

59k

GATE

10k

1N5245

15V

D2*

SMAJ58CA

*DIODES INC.

CTMR

47nF

*SANYO 25CE22GA

RSNS

10m

IRLR2908

SMAJ58A

VIN

43563 F09

LT4356DE-3

GND

TMR

OUT

GATE

SNS

IN+

SHDN

AOUT

FAULT

FLT

UNDERVOLTAGE

CL*

22µF

DC-DC

CONVERTER

GND

SHDN

VCC

4.99k

383k

100k

59k

VCC

Figure 9. Overvoltage Regulator with Low-Battery Detection

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