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reference voltage reaches 0.6V). The reference used in this case to determine the UV thresholds is the

increasing voltage driven by the 2048 soft start digital counter while the reference used for the OV

threshold is the final reference programmed by the VID pins or available on the REF_IN/OUT pin.

Figure 13. UVP Protection & Hiccup Mode.

3.8 SOFT START AND INHIBIT

At start-up a ramp is generated increasing the loop reference from 0V to the final value programmed by

VID in 2048 clock periods as shown in Figure 14.

Once the soft start begins, the reference is increased: upper and lower Mosfets begin to switch and the

output voltage starts to increase with closed loop regulation. At the end of the digital soft start, the Power

Good comparator is enabled and the PGOOD signal is then driven high (See Figure 14).

The Under Voltage comparator is enabled when the increasing reference voltage reaches 0.6V while OVP

comparator is always active with a threshold equal to the +15%_min of the final reference.

The Soft-Start will not take place, if both VCC and VCCDR pins are not above their own turn-on thresholds.

During normal operation, if any under-voltage is detected on one of the two supplies the device shuts

down. Forcing the OSC/INH pin to a voltage lower than 0.5V (Typ.) disables the device: all the power mos-

fets and protections are turned off until the condition is removed.

Figure 14. Soft Start.

CH1=PGOOD; CH2=Vout; CH3=REF_OUT; CH4=Iout

PGOOD

t

t

t

t

Turn ON threshold

2048 Clock Cycles

Timing Diagram

Acquisition:

CH1=PGOOD; CH2=VOUT; CH3=REF_OUT