L6711 datasheet(33/50 Pages) STMICROELECTRONICS

33 / 50 page

L6711

Output voltage monitor and protections

33/50

Output voltage monitor and protections

The device monitors through pin VSEN the regulated voltage in order to manage the OVP /

UVP conditions.

14.1

UVP protection

If the output voltage monitored by VSEN drops below the 60% of the reference voltage for

more than one clock period, the device turns off all mosfets and the OSC/FAULT is driven

high (5V). The condition is latched; to recover it is required to cycle Vcc or the OUTEN pin.

14.2

Programmable OVP protection

Once VCC crosses the turn-ON threshold and the device is enabled (OUTEN = 1), the

device provides a programmable Over Voltage protection; when the voltage sensed

overcomes the programmed threshold, the controller permanently switches on all the low-

side mosfets and switches off all the high-side mosfets in order to protect the load. The

OSC/ FAULT pin is driven high (5V) and power supply or OUTEN pin cycling is required to

restart operations.

The OVP threshold is programmed through the OVP pin: leaving the pin floating, it is

internally pulled-up and the threshold is set at 115% (Typ.) of the programmed output

voltage. Connecting the OVP pin to SGND through a resistor ROVP, the OVP threshold

becomes a fixed voltage as follow:

OVPTH = 1.455 · ROVP · 12.5µ

14.3

Preliminary OVP protection (Pre-OVP)

While VCC pin is under the turn-ON threshold, a preliminary-OVP protection turns on the

low side mosfets as long as the FBR pin voltage is greater than 1.8V. This protection is

enabled when VCC stays within the device turn-on threshold and the PreOVP turn on

threshold and depends also on the OUTEN pin status as detailed in Figure 16 - left.

A simple way to provide protection to the output in all conditions when the device is OFF

(then avoiding the unprotected red region in Figure 16) consists in supplying the controller

through the 5VSB bus as shown in Figure 16 - right.

Both Over Voltage and Under Voltage are active also during soft start (see the relevant

section).

L6711 Datasheet(PDF) 33 Page - STMicroelectronics