L9380 datasheet(10/18 Pages) STMICROELECTRONICS

10 / 18 page

Functional description

L9380

10/18

In application which don’t use the overload protection or if one channel is not used, the

Timer pin of this channel must be connected to ground and the drain pin with a resistor to

Vbat.

The timing characteristic illustrates the function and the meaning of VDSmin and Toff (see

Figure 6). The input current of the overload sense comparator is specified as ISmax. The sum

IPR + IDmax generates a drop across the external resistor RD if the drain pin voltage is higher

than the source pin (see Figure 4). In the switching point the comparator input source pin

currents are equal and the half of the specified current ISmax. For an offset compensation

equal external resistors (RD = RS) at drain and source pin are imperative. The drain sense

comparator, which detects the overload, has a symmetrical hysteresis of 20 mV (see

Figure 5).

Exceeding the source pin voltage by 10 mV with respect to the drain voltage forces the timer

capacitor to discharge. Decreasing the source pin voltage 10 mV lower than the drain pin

voltage an overload of the external MOS is detected and the timer capacitor will be loaded.

After reaching a voltage at pin CT higher than the timer threshold VThi the influenced

channel is switched off. In this case the overload is stored in the timer capacitor.

The timer capacitor will be discharged with a ’High’ signal at the input (see Figure 3). After

reaching the lower timer threshold VTLo the overload protection is reset and the channel is

able to switch on again.

Figure 3.

Timing characteristic

Figure 4.

Drain, source input current.

VIN

4.4V

0.4V

VDSmin

Toff

D98AT392

IPR + IDmax

ISmax

V S

IPR

D98AT393

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