PM8903 datasheet(16/34 Pages) STMICROELECTRONICS

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Device description

PM8903

16/34

Doc ID 022748 Rev 1

The protection is triggered when the voltage sensed on the FB pin rises over the OVP

threshold (0.72 V typ.) and the device acts as follows:

●

HS MOSFET is suddenly forced OFF

●

LS MOSFET is turned on (to discharge the output and protect the load) until VFB drops

to 0.3 V, then it is turned off (to avoid negative spikes on output voltage). If VFB

recrosses OVP rising threshold, LS is turned on again

This protection state is latched, cycle EN or VCC to recover.

5.3.2

Undervoltage protection

Undervoltage protection is active from the end of soft-start.

If VFB falls below the UVP threshold (0.48 V typ.), undervoltage protection is triggered and

the device starts a soft-off sequence (see

Section 5.2.2).

This protection state is latched, cycle EN, VCC or VIN to recover.

5.3.3

Feedback disconnection protection

In order to protect the load even if the FB pin is not connected to the PCB, a 100 nA current

is constantly sourced from the FB pin: if the FB pin is left floating, it is internally pulled high

triggering OVP protection and preventing VOUT from rising out of control.

Figure 10.

FB disconnection

5.3.4

Power Good (PGOOD)

PGOOD is an open drain output, left floating when VOUT is in regulation at the programmed

voltage, at the end of soft-start.

PGOOD is forced low, to communicate that the output voltage is no longer in regulation, if

one of the following conditions is verified:

●

The voltage of the FB pin exits from the PGOOD window (

±20% of V

REF)

●

The device is disabled, EN is forced low

●

VCC voltage is below the UVLO threshold

●

Any protection is triggered (OVP, UVP, OCP, OTP)

ROS

RFB

VOUT

720mV

OVP

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