L497 datasheet(7/11 Pages) STMICROELECTRONICS

7 / 11 page

Figure 2 : SRC : Icoil Failure and Time Dependence of Active Region.

Figure 3 : Permanent Conduction Protection.

HJ : Input signal

IC : Coil current

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 value forcingthe 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).

L497

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L497 Datasheet(PDF) 7 Page - STMicroelectronics