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LTC1421/LTC1421-2.5

APPLICATIONS INFORMATION

time point 2). Pulses less than 20ms on POR are ignored.

CPON goes low. Both GATEHI and GATELO will be

actively pulled down to GND. When VOUTLO drops below

its reset threshold voltage, PWRGD will immediately pull

low (time point 3) followed by RESET and DISABLE 32

µs

later (time point 4). Both supplies will be discharged to

ground and stay there until POR is pulled high.

The circuit breaker can be reset by pulling POR low. After

POR is low for more than 20ms, the chip will immediately

try to power up the supplies.

Circuit Breaker Timing

The waveforms for the circuit when a short occurs on

either supply during board insertion are shown in

Figure 16. Time points 1 to 4 are the same as the board

insertion example, but at time point 5, a short circuit is

detected on one of the supplies. The charge pumps are

immediately turned off, the outputs VOUTHI and VOUTLO are

actively pulled to GND and the CPON and FAULT pins are

pulled low. At time point 6, the circuit breaker is reset by

pulling POR low. After POR has been low for 20ms (time

point 7), CPON and FAULT are pulled high, the 20

µA

reference current is connected to RAMP and the charge

pumps are enabled. VOUTHI and VOUTLO ramp up at a

controlled rate. When VOUTLO has exceeded its reset

threshold, the PWRGD signal is pulled high (time point 8).

After a 200ms delay, RESET is pulled high and DISABLE

goes low.

Figure 16. Circuit Breaker Timing

VCCLO

VCCHI

DISABLE

CON1

CON2

CPON

PWRGD

VTH1

1421 F16

VOUTHI

GATEHI

GATELO

VOUTLO

RESET

FAULT

POR

20ms

200ms

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