L6728D datasheet(13/33 Pages) STMICROELECTRONICS

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L6728D

Overcurrent protection

Doc ID 16498 Rev 1

13/33

Overcurrent protection

The overcurrent function protects the converter from a shorted output or overload, by

sensing the output current information across the low side MOSFET drain-source on-

resistance, RDS(on). This method reduces cost and enhances converter efficiency by

avoiding the use of expensive and space-consuming sense resistors.

The low side RDS(on) current sense is implemented by comparing the voltage at the PHASE

node when the LS MOSFET is turned on with the programmed OCP threshold voltages,

internally held. If the monitored voltage is higher than these thresholds, an overcurrent event

is detected.

For maximum safety and load protection, the L6728D implements a dual-level overcurrent

protection system:

●

1st level threshold: This is the user externally-set threshold. If the monitored voltage

on PHASE exceeds this threshold, a 1st level overcurrent is detected. If four 1st level

OC events are detected in four consecutive switching cycles, overcurrent protection is

triggered.

●

2nd level threshold: This is an internal threshold whose value is equal to the 1st level

threshold multiplied by a factor 1.5. If the monitored voltage on PHASE exceeds this

threshold, overcurrent protection is triggered immediately.

When overcurrent protection is triggered, the device turns off both the LS and HS MOSFETs

in a latched condition.

To recover from an overcurrent protection-triggered condition, the VCC power supply must

be cycled.

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