L99MOD50XP datasheet(24/42 Pages) STMICROELECTRONICS

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Application information

L99MOD50XP

24/42

DS12615 Rev 4

3.14

Programmable soft-start function to drive loads with higher

inrush current

Loads with start-up currents higher than the over-current limits (e.g. inrush current of lamps,

start current of motors and cold resistance of heaters) can be driven by using the

programmable softstart function (i.e. overcurrent recovery mode). Each driver has a

corresponding over-current recovery bit. If this bit is set, the device automatically switches

the outputs on again after a programmable recovery time. The duty cycle in over-current

condition can be programmed by the SPI interface to about 12% or 25%. The PWM

modulated current provides sufficient average current to power up the load (e.g. heat up the

bulb) until the load reaches operating condition. The PWM frequency settles at 1.7 kHz and

3 kHz. The device itself cannot distinguish between a real overload and a non linear load

like a light bulb. A real overload condition can only be qualified by time. For over-load

detection the microcontroller can switch on the light bulbs by setting the over-current

recovery bit for the first e.g. 50 ms. After clearing the recovery bit the output is automatically

switched off, if the overload condition remains. This over-load detection procedure has to be

followed in order make it possible to switch on the low-side driver of a bridge output, if the

associated high-side driver has been used in recovery mode before.

Figure 8. Example of programmable soft-start function for inductive loads

L99MOD50XP Fiches technique(PDF) 24 Page - STMicroelectronics