L3751 datasheet(21/41 Pages) STMICROELECTRONICS

21 / 41 page

Figure 21. Constant current in persistent short-circuit

Figure 22. Hiccup in persistent short-circuit

The L3751 implements an improved pulse-by-pulse valley current sensing thanks to dedicated control logic for

an effective current protection over the duty cycle range. The device supports programmable valley current

monitoring across an optional sensing resistor for the best reading accuracy or across the on-state RSDON of the

low-side MOSFET to minimize the conduction losses, as shown in Figure 17.

The valley current threshold is easily programmed with series RILIM resistor connected from ILIM pin to the

selected sensing element (see Figure 17). As soon as the LO gate signal is driven high an internal generator

source a constant current out of the ILIM pin so the pin voltage is:

VILIMt = RILIM+Rx ∙IILIM−Rx∙IVYt ≈RILIM∙IILIM−Rx∙IVYt

(5)

where RX can be the low-side RDSON or the shunt resistor. An internal comparator monitors the pin voltage and

keeps the low LO signal high until it drops to VILIM TH threshold (- 2 mV typ.)

IILIM= 200μAat TJ=27℃ in case of RDSON lossles sensing

100μAat TJ=27℃ in case of precise sensing on sℎunt resistor

(6)

L3751

Overcurrent protection

DS13841 - Rev 1

page 21/41

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