Figure 2 : SRC : Icoil Failure and Time Dependence of Active Region.
L497
HJ : Input signal
IC : Coil current
Figure 3 : Permanent Conduction Protection.
VCM : Voltage on capacitor CSRC.
DST : Percentage of imposed desaturation time.
PERMANENT CONDUCTION PROTECTION
(fig. 3)
The permanent conduction protection circuit moni-
tors the input period, chargingCP with a costantcur-
rent when the sensor signal is high and discharging
it when the sensor signal is low. If the input remains
high for a time longer than TP the voltage across CP
reachesan internallyfixed valueforcingthe slow de-
crease of coil current to zero. A slow decrease is
necessary to avoid undesired sparks. When the in-
put signal goes low again CP is swiftly discharged
and the current control loop operates normally.
The delay time TP is given by :
TP (sec) = 18 CP R7
Where R7 is the biasing resistor on pin 12 (in K) and
Cp the delay capacitor at pin 9 (in µF).
7/11