F72820

Jul 2007

V0.24P

-5-

F72820

12V

VOUT

Q1

Q2

UGATE

LGATE

PHASE

BOOT

VCC

Regulator

5V

Figure 4

6.3 Soft-Start

The POR function initiates the digital soft-start sequence; the soft start function is used to prevent surge current from

power supply input during power on. When soft start event, PWM error amplifier reference inputs are forced to track

a voltage level proportional to the soft-start voltage. As the soft-start voltage slews up, the PWM comparator

regulates the output relative to the tracked soft-start voltage, slowly charging the output capacitor(s), the soft start

duration is 3mS in typical case.

TIME

0V

3V

6V

3mS

VCC

VOUT

Figure 5

6.4 Over-current Protection

programs the over-current tripping level of the PWM converter. As show on Figure 6, the internal 40uA current sink

when UGATE is high and PHASE voltage is under OCSET voltage. When OC be detected, over current protect

function will soft start three times and check over current again. If over current event is true, the F72820 will be shut

down.