LTC3421 datasheet(10/16 Pages) LINER

10 / 16 page

LTC3421

3421f

OPERATIO

The circuit connected to BURST should be able to sink or

source up to 2mA. Note that Burst Mode operaton is

inhibited during start-up and soft-start.

Note that if VIN is above VOUT – 0.3V, the part will exit Burst

Mode operation and the synchronous rectifier will be

disabled.

Note that if the load applied during forced Burst Mode

operation exceeds the current that can be supplied, the

output voltage will start to droop and the part will auto-

matically come out of Burst Mode operation and enter fixed

frequency mode, raising VOUT. The maximum current that

can be supplied in Burst Mode operation is given by:

Simplified Diagram of Automatic Burst Mode Control Circuit

MODULATOR

CLAMP

0.5V TO 1V

SLEEP

3421 TA03

ERROR AMP/

SLEEP COMP

RCOMP

CCOMP

VREF

±1%

–

9 BURST

0.9V/

1.1V

SSDONE

MODE

1 = Burst Mode

OPERATION

0 = PWM MODE

SSDONE

VREF

–4%

VCC

1mA

IOUT/3000

in amps

O MAX

OUT

()

•

–

()

055

OUTPUT DISCONNECT AND INRUSH LIMITING

The LTC3421 is designed to allow true output disconnect

by eliminating body diode conduction of the internal

P-channel MOSFET rectifier. This allows VOUT to go to zero

volts during shutdown without drawing any current from

the input source. It also allows for inrush current limiting

at turn-on, minimizing surge currents seen by the input

supply. Note that to obtain the advantages of output

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