LTC2925IGN datasheet(11/20 Pages) LINER

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LTC2925

2925f

Status Output

The STATUS pin provides an indication that the supplies

are finished ramping up. This pin is an open-drain output

that pulls low until the GATE has been fully charged. Since

the GATE pin drives the gate of the external FET, or the

RAMP pin directly when no FET is used, the supplies are

completely ramped up when the GATE pin is fully charged.

The STATUS pin will go low again when the GATE pin is

pulled low, either because of a short-circuit fault, a power

good timeout fault, or because the ON pin has been pulled

low.

Fault Output

The FAULT pin is an open-drain output that pulls low when

the electronic circuit breaker is activated due to a short-

circuit or power good timeout fault. FAULT is reset by

pulling ON below 0.4V. The supplies will not be allowed to

ramp up again until the SCTMR, PGTMR, and SDTMR pins

are below about 100mV, and the ON pin is pulled above

1.23V.

APPLICATIO S I FOR ATIO

RSENSE

0.1

µF

CPGTMR

VCC SENSEP SENSEN

VIN

RONB

VIN

RTB1

RTB2

RFA2

SLAVE2

MASTER

RFB2

RTA2

RTB3

RTA3

RTA1

RONA

RAMPBUF

TRACK1

TRACK2

TRACK3

FB2

GATE

LTC2925

PGTMR

CSDTMR

SDTMR

CSCTMR

SCTMR

GND

2925 F09

RAMP

RFA3

SLAVE3

RFB3

DC/DC

OUT

DC/DC

RUN/SS

OUT

FB3

VIN

PGI

RFA1

SLAVE1

RFB1

SUPPLY

MONITOR

DC/DC

RUN/SS

OUT

FB1

FAULT

10k

VIN

STATUS

REMOTE

RST

SD3

SD2

SD1

CGATE

Ω

Figure 9. Retry on Fault

Retry on Fault

The LTC2925 continuously attempts to ramp up the out-

puts after a fault if the FAULT pin is tied to the ON pin

(Figure 9). If a short-circuit fault occurs in this configura-

tion, the SCTMR pin ramps up the CSCTMR capacitor with

µA until it reaches 1.23V. Then, GATE is pulled low turn-

ing off the shorted FET. At the same time, the FAULT pin’s

open-drain output pulls ON low. The CSCTMR capacitor is

pulled down with 2

µA until it reaches about 100mV. After

the CSCTMR capacitor reaches 100mV, the shutdown timer

begins and upon completing a shutdown timer cycle, the

supplies start ramping up again. If there is no short-circuit

this time, the supplies will come up normally. Otherwise,

the retry cycle will repeat. If a longer off time is required

between retry attempts, the CSDTMR capacitor value can be

increased, providing a greater delay before the FET’s GATE

ramps up on each cycle. Note that tying FAULT to ON also

causes the LTC2925 to retry on Power Good Timeout faults.

In this mode, verify that the slave supplies’ current limits

provide sufficient protection under short-circuit conditions.

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