Datasheet

Functional description L9935
16/29 Doc ID 5198 Rev 10
next data transfer took place. After detection of a short to V
S
we suggest to turn off the
corresponding bridge to reduce power dissipation for at least 1ms.
5.5 Diagnosis of a short to V
S
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 V
S
.
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 V
S
Between t
on
and t
short
the over current detection is totally blanked.
Between t
short
and t
PWM
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 t
PWM
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 t
PWM
so no error flag is set
during normal pulse width modulation.
'!0'03
T
T
/.
)
1
SHORTTHRESHOLD
T
ON
TURNONOFTHESINKTRANSISTOR
T
ON
T

T
SHORT
ACTIVATIONOFSHORTTHRESHOLD
T
ON
T
DELAY
T
07-
ACTIVATIONOF07-THRESHOLD
07-THRESHOLD
07-DETECTION
SIGNALINTERNAL
3HORTDETECTION
SIGNALINTERNAL
%RROR
T
SHORT
T
07-
T
/.
T
/.
T
/.
T
SHORT
T
SHORT
T
07-
T
SHORT
T
07-
T
07-
T
T
T