When also the Toff interval has expired, the out-

put power MOS is switched ON.

Now two conditions may occur

- the overload is still present. In this case the out-

put power MOS is again driven in linear mode

(limiting the output current to Isc) for another Ton,

starting a new cycle, or

- the overload condition is removed, and the out-

put power MOS is no longer driven in linear

mode.

All these occurrences are presented on the DIAG

pin (see fig 2). We call this unique feature Non

Dissipative Short Circuit Protection and it en-

sures a very safe operation even in permanent

overload conditions. Note that, of course, choos-

ing the most appropriate value for the Ton interval

(i.e. the value of the Cdon capacitor) a delay (the

Ton itself) will prevent that a misleading Short Cir-

cuit information is presented on the DIAG output,

when driving capacitive loads (that acts like short

circuit in the very beginning) or Incandescent

Lamp (a cold filament has a very low resistive

value).

The Non Dissipative Short Circuit Protection can

be disabled (keeping Ton = 0 but with the output

current still limited to Isc, and Diagnostic dis-

abled) simply shorting to ground the the ON DE-

LAY pin.

DEMAGNETISATION OF INDUCTIVE LOADS

The L6377 has an internal clamping zener diode

able to demagnetise inductive loads. Note that

the limitation comes from the peak power that the

package can handle. Attention must be paid to a

proper thermal design of the board. If, for what-

ever reason (load current or inductive value too

big) the peak power dissipation is too high, an ex-

ternal Zener plus Diode arrangement, can per-

form a demagnetisation versus Ground or versus

Vs (see fig 5 and 6). The breakdown voltage of

the external Zener Diode must be chosen consid-

ering the internal clamping voltage (Vcl) and the

supply voltage (Vs) according to:

Vz< Vcl(min)-Vs(max)

for demagnetisation versus Ground or

Vs(max)<Vz<Vcl(min)

for demagnetisation versus Vs.

Vi+

Vs

Vout

100mV

D94IN079

Vi-

100mV

Figure 4: Input Comparator Hysteresis

L6377

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