DocID025003 Rev 1

15/29

A6727

Output voltage monitor and protections

8

Output voltage monitor and protections

The A6727 monitors the voltage at FB pin and compares it to internal reference voltage in

order to provide undervoltage and overvoltage protections.

8.1

Undervoltage protection

If the voltage at FB pin drops below UV threshold (0.6 V typ.), the device turns off both HS

and LS MOSFETs, waits for 2048 clock cycles and then performs a new soft-start. If

undervoltage condition is not removed, the device enters the hiccup mode with a typical

period of 13.6 ms.

UVP is active from the end of soft-start.

8.2

Overvoltage protection

If the voltage at FB pin rises over OV threshold (1 V typ.), overvoltage protection turns off

HS MOSFET and turns on LS MOSFET overriding PWM logic as long as overvoltage is

detected.

OVP is always active with top priority as soon as the overcurrent threshold setting phase

has been completed.

8.3

Feedback disconnection protection

In order to provide load protection even if FB pin is not connected, a 100 nA bias current is

always sourced from this pin. If FB pin is not connected, this current permanently pulls up

FB over OVP threshold: thus LS is latched on preventing output voltage from rising out of

control.

8.4

Undervoltage lock out

In order to avoid anomalous behaviors of the device when the supply voltage is too low to

support its internal rails, UVLO is provided: the device starts up when VCC reaches UVLO

upper threshold and shut downs when VCC drops below UVLO lower threshold.