LTC2913 datasheet(14/24 Pages) AD

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LT4356-3

Rev D

For more information www.analog.com

Figure 5.

Figure 6. Auxiliary LDO Output with Optional Current Limit

43563 F05

LT4356-3

GATE

IN4148W

*4.7

D1*

BAV99

2N2905A OR

BCP53

249k

47nF

INPUT

2.5V OUTPUT

≈ 150mA MAX

*OPTIONAL FOR

CURRENT LIMIT

LT4356DE-3

AOUT

RLIM

100k

249k

43563 F06

IN+

10µF

R4 + R5

VOUT = 1.25

ILIM ≈

0.7

RLIM

APPLICATIONS INFORMATION

The LT4356-3 does not need extra compensation compo-

nents at the GATE pin for stability during an overvoltage

or overcurrent event. However, with fast, high voltage

transient steps at the input, a gate capacitor, C1, to ground

is needed to prevent turn-on of the N-channel MOSFET.

The extra gate capacitance slows down the turn off time

during fault conditions and may allow excessive current

during an output short event. An extra resistor, R1, in

series with the gate capacitor can improve the turn off

time. A diode, D1, should be placed across R1 with the

cathode connected to C1 as shown in Figure 5.

tions. This diode causes extra power loss, generates heat,

and reduces the available supply voltage range. During

cold crank, the extra voltage drop across the diode is

particularly undesirable.

The LT4356-3 is designed to withstand reverse voltage

without damage to itself or the load. The VCC, SNS, and

SHDN pins can withstand up to 60V of DC voltage below

the GND potential. Back-to-back MOSFETs must be used

to eliminate the current path through their body diodes

(Figure 7). Figure 8 shows the approach with a P-Channel

MOSFET in place of Q2.

Figure 7. Overvoltage Regulator with N-channel MOSFET

Reverse Input Protection

CTMR

0.1µF

RSNS

10m

IRLR2908

VIN

12V

VOUT

12V, 3A

CLAMPED

AT 16V

43563 F07

LT4356DE-3

GND

TMR

OUT

SNS

SHDN

AOUT

IN+

VCC

FLT

D2*

SMAJ58CA

4.99k

59k

GATE

10k

2N3904

1N4148

*DIODES INC.

Auxiliary Amplifier

An uncommitted amplifier is included in the LT4356-3 to

provide flexibility in the system design. With the negative

input connected internally to the 1.25V reference, the

amplifier can be connected as a level detect comparator

with external hysteresis. The open collector output pin,

AOUT, is capable of driving an opto or LED. It can also

interface with the system via a pull-up resistor to a supply

voltage up to 80V.

The amplifier can also be configured as a low dropout

linearregulatorcontroller.WithanexternalPNPtransistor,

such as 2N2905A, it can supply up to 100mA of current

with only a few hundred mV of dropout voltage. Current

limit can be easily included by adding two diodes and one

resistor (Figure 6). The amplifier is turned off when the

LT4356-3 is shut down.

Reverse Input Protection

A blocking diode is commonly employed when reverse

input potential is possible, such as in automotive applica-

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