L9954TR datasheet(22/37 Pages) STMICROELECTRONICS

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Application information

L9954 / L9954XP

22/37

Doc ID 14279 Rev 4

3.13

Programmable softstart 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 will automatically switch-

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

condition can be programmed by the SPI interface to be about 15% ...25%. The PWM

modulated current will provide 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 1.5 kHz

or 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. As an example the

microcontroller can switch on light bulbs by setting the over-current recovery bit for the first

50ms. After clearing the recovery bit the output will be automatically disabled if the overload

condition still exits.

Figure 9.

Example of programmable softstart function for inductive loads

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