SC2603 datasheet(5/11 Pages) SEMTECH

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SC2603

POWER MANAGEMENT

Application Information

Over Current Protection

The over-current protection is implemented by a sensing

resistor and an internal current-limit comparator with a

threshold of 70mV. If the switching current through the

sensing resistor causing voltage to drop at the CS pin

reachs 70mV, the SC2603 will immediately turn the gate

pulse off to limit the current through the power switch.

The figure below shows over-current waveforms. At t1,

the input current I

IN begins to increase as the load IOUT

builds up until it hits the OCP threshold at t2. At t2, V

OUT

begins to drop as I

OUT starts increasing toward t3 while VIN

and I

IN remain the same. At t3, there two events are

happening. 1) V

OUT is at half of its regulating voltage. At

this point, the internal oscillator runs into frequency shift

mode and shifts the frequency to one fourth of the oper-

ating frequency. 2) The diode starts conducting current

without limit causing V

IN to fall due to supply current limit.

Finally, V

IN and VOUT both drops to zero and IIN becomes the

input supply current limit.

A RC filter at the CS pin is necessary to filter out noise to

ensure accurate sensing.

The value of the sensing resistor can be caculated by

the following equation:

PEAK

Where I

PEAK is the input peak current through the power

MOSFET.

OUT

IOUT

IIN

Over Current Waveforms

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