L6756D datasheet(26/36 Pages) STMICROELECTRONICS

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Output voltage monitoring and protections

L6756D

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Output voltage monitoring and protections

L6756D monitors through pin VSEN the regulated voltage in order to manage OV and UV.

The device shows different thresholds when in different operative conditions but the

behavior in response to a protection event is still the same as described below.

6.1

Overvoltage

Once VCC crosses the turn-ON threshold and the device is enabled (EN = 1), L6756D

provides an overvoltage protection by sensing the regulated voltage through VSEN: when it

overcomes the programmed VID +200 mV (max) the controller:

–

Permanently sets Gx to zero keeping DRVON high in order to keep all the low-side

MOSFETs on to protect the load.

–

Drives the OSC/ FLT pin high.

–

Power supply or EN pin cycling is required to restart operations.

6.2

Feedback disconnection

This feature acts in order to stop the device from regulating dangerous voltages in case the

remote sense connections are left floating. The protection is available for both the positive

and negative sense.

According to what reported in Figure 11, the protection works as follow:

–

Positive sense consider to monitor the CORE output voltage through both VSEN

and CSxN. As soon as CSxN is more than 650 mV higher than VSEN, the device

latches with all Gx set to HiZ and DRVON set to zero. FLT pin is driven high. In any

case, the 50

μA pull-down current on the VSEN (offset) forces the device to detect

the fault condition.

–

Negative sense consider to monitor the internal opamp used to recover the SGND

losses by comparing its output and the internal reference generated by the DAC.

As soon as the difference between the output and the input of this opamp is higher

than 500mV, the device latches with all Gx set to HiZ and DRVON set to zero. FLT

pin is driven high.

–

To recover from a latch condition, cycle VCC or EN.

Figure 11.

FB disconnection protection

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