Functional description

L9935

16/29

Doc ID 5198 Rev 10

next data transfer took place. After detection of a short to VS we suggest to turn off the

corresponding bridge to reduce power dissipation for at least 1ms.

5.5

Diagnosis of a short to VS

During the short current through the sink transistor will rise more rapidly than under normal

load conditions. Reaching a peak current of 1.5 times the maximum PWM current between

typically 2 µs and 5 µs

after turn on will be detected as a short to VS.

Detecting a short the low side transistor will try to turn on again the next 7 trigger pulse of

the oscillator.

Simultaneously the error flag will updated on each pulse.

Figure 8.

Normal PWM current versus short circuit current and detection of short

to VS

Between ton and tshort the over current detection is totally blanked.

Between tshort and tPWM the current threshold is set to 1.5 times the maximum PWM current

(1.5 times the current of current setting LL).

Overcurrent now will set the error flag.

After tPWM the current threshold is the nominal PWM current set by the external resistor.

Exceeding this current will just turn off the sink transistor. This is considered as normal

operation. The error flag is detached from the comparator after tPWM so no error flag is set

during normal pulse width modulation.