L9953LXP

Application information

Doc ID 16185 Rev 3

23/35

3.13

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 soft start 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 12% or 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 3kHz or

6kHz. 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.

Programmable soft start function for inductive loads and incandescent

bulbs

Load Current

Overcurrent

detection

Unlimited Inrush Current

Limited Inrush Current in

overcurrent recovery mode

with inductive load

t

Load Current

Overcurrent

detection

Unlimited Inrush Current

Limited Inrush Current in

overcurrent recovery mode with

incandescent bulb

t