UCC2913

UCC3913

SLUS274A – JANUARY 1999 – REVISED APRIL 2003

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APPLICATION INFORMATION

source, I2, until 0.5 V is reached. Once the voltage at CT reaches 0.5 V, the fault latch resets, which re-enables

the output and allows the fault circuitry to regain control of the charging switch. If a fault is still present, the fault

comparator closes the charging switch causing the cycle to begin. Under a constant fault, the duty cycle is given

by:

Duty Cycle

+

1

mA

I

Average power dissipation in the pass element is given by:

P

IMAX

1

mA

I

I

V

FET

R

PL

Duty Cycle

+

1

mA

R

PL

V

FET

Therefore, the maximum average power dissipation in the MOSFET can be approximated by:

P

IMAX

1

mA

R

PL

V

FET

+ IMAX

1

mA

R

PL

MOSFET pass element.

Overload Comparator

occur if the output MOSFET is not responding to a command from the device) the CT pin begins charging with

I3, 1 mA, and continue to charge to approximately 8 V. This allows a constant fault to show up on the SD/FLT

pin, and also since the voltage on CT charges past 2.5 V only in an overload fault mode, it can be used for

detection of output FET failure or to build in redundancy in the system.

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