LTC2925 View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
'LTC2925' PDF : 26 Pages View PDF
LTC2925
APPLICATIONS INFORMATION
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.
Retry on Fault
The LTC2925 continuously attempts to ramp up the outputs
after a fault if the FAULT pin is tied to the ON pin (Figure 9).
If a short-circuit fault occurs in this configuration, the
SCTMR pin ramps up the CSCTMR capacitor with 50μA until
it reaches 1.23V. Then, GATE is pulled low turning 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 2μA 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.
12
RSENSE
Q1
VIN
0.1μF
10Ω
CGATE
RONB
RONA
VIN
VCC SENSEP SENSEN GATE
ON
REMOTE
RAMP
PGI
SD1
FB1
MASTER
SUPPLY
MONITOR
RST
VIN
RUN/SS IN
DC/DC
FB
OUT
10k
RTB1
RTA1
RTB2
RTA2 RTB3
RTA3
STATUS
LTC2925
SD2
FAULT
FB2
RAMPBUF
TRACK1
TRACK2
SD3
FB3
TRACK3
GND SCTMR SDTMR PGTMR
CSCTMR
CSDTMR
CPGTMR
RFA1
RFB1
VIN
RUN/SS IN
DC/DC
FB
OUT
RFA2
RFB2
VIN
RUN/SS IN
DC/DC
FB
OUT
RFB3
RFA3
2925 F09
Figure 9. Retry on Fault
SLAVE1
SLAVE2
SLAVE3
2925fc
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