PM8908 datasheet(16/28 Pages) STMICROELECTRONICS

16 / 28 page

Device description

PM8908

16/28

DocID027688 Rev 3

Figure 7. PM8908 startup time diagram

Soft-off

The PM8908 implements the soft-off sequence turning off both the HS and LS MOSFETs

and connecting the integrated discharge resistor (47

) between the PHASE and PGND

pin.

The PM8908 begins the soft-off sequence, and remains in a latched state, if one of the

following conditions occurs:



VCC voltage falls below UVLO threshold



OVP (overvoltage protection)



UVP (undervoltage protection)



EN pin is pulled low.

The cycling VCC and EN the IC recover from the latched state with a new soft-start

sequence.

5.4

Output voltage monitoring and protection

The PM8908 monitors the output voltage status through the VOUT pin and compares the

voltage on this pin with the REFIN voltage in order to provide over and undervoltage

protection as well as the PGOOD signal.

5.4.1

Overvoltage protection

Overvoltage protection is active as soon as the device is enabled, the VCC is above the

respective undervoltage lockout level and REFIN is higher than 300 mV.

dc= 550 us(typ)

PM8908

Latches UVP

PM8908 will not perform any

SS by itself but will follow

REFIN as it is observable on

REFIN pin. REFIN need to

have an external SS.

d=750 us(typ)

Case 1

Case 3

Case 2

9 ms(typ)

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