L99MC6 datasheet(16/55 Pages) STMICROELECTRONICS

16 / 55 page

Description

L99MC6

16/32

Doc ID 16523 Rev 2

2.7

Bulb mode (programmable soft start function to drive loads

with higher inrush current)

Loads with start-up currents higher than the overcurrent limits (for example inrush current of

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

programmable soft start function (that is overcurrent recovery mode). Each driver has a

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

on the outputs again after a fixed recovery time. The PWM modulated current provides

sufficient average current to power up the load (for example heat up the bulb) until the load

reaches operating condition (Figure 6).

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 overcurrent recovery bit for the first

50 ms. After clearing the recovery bit, the output is automatically disabled if the overload

condition still exits.

Figure 7.

Example of programmable soft start function for inductive loads and incandescent

bulbs

Load Current

Unlimited Inrush Current

Limited Inrush Current in

overcurrent recovery

mode with inductive load

Load Current

Unlimited Inrush Current

Limited Inrush Current in

overcurrent recovery mode

with incandescent bulb

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