LTC1421 datasheet(32/40 Pages) LINER

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LTC4211

4211fb

APPLICATIONS INFORMATION

VCC

TIMER

GATE

RESET

FILTER

>VREF – 80mV

FAULT

VOUT

GATE

VOUT

A B C

SLOW COMPARATOR ARMED

IF OVERVOLTAGE GOES

AWAY, SECOND CYCLE

CONTINUES

OVERVOLTAGE

IF ANY FAULT HAPPENS

AFTER THIS POINT, THE

CIRCUIT BREAKER TRIPS

AND

FAULT LATCHES LOW

OVERVOLTAGE CIRCUIT BREAKER

TRIPS, GATE PULLS DOWN AND

FAULT LATCHES LOW

FAULT IS PULLED LOW (BUT NOT LATCHED)

DUE TO A START-UP OVERVOLTAGE PROBLEM

POWER GOOD

VFB > VREF

POWER BAD

VFB < VREF

FPD

4211 F24

>VREF

FAULT

LATCHED LOW

Low Side (Output) Overvoltage Protection

A Zener diode can be used in a similar fashion to detect/

protect the system against a supply overvoltage condition

on the load (or low) side of the pass transistor. In this

case, the Zener diode is connected from the load to the

LTC4211’s FILTER pin, as shown in Figure 25. An additional

diode, D1, prevents the FILTER pin from pulling low during

an output short-circuit. Figure 26 illustrates the timing

diagram for a low side output overvoltage condition. In

this example, VCC starts up in an overvoltage condition

but the LTC4211 can only sense the overvoltage supply

condition at Time Point 6 when the GATE pin has ramped

up. At Time Point 6, VFILTER is greater than 1.236V, the

circuit breaker is tripped, the GATE pin voltage is pulled

to ground and FAULT is asserted low and latched.

Figure 24. High Side Overvoltage Protection

LTC1421 Datasheet(PDF) 32 Page - Linear Technology

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