L99MM70XP datasheet(20/68 Pages) STMICROELECTRONICS

20 / 68 page

Description

L99MM70XP

20/68

Doc ID 022637 Rev 2

3.10.4

Cross current protection

The half bridges of the device are cross current protected by an internal delay time. If one

driver (LS or HS) is turned off, the activation of the other driver of the same half bridge is

automatically delayed by the cross current protection time. After the cross current protection

time is expired, the slew-rate limited switch off phase of the driver is changed to a fast turn-

off phase and the opposite driver is turned on with slew-rate limitation. Due to this behavior,

it is always guaranteed that the previously activated driver is completely turned off before

the opposite driver starts to conduct.

3.10.5

Programmable soft start function

Loads with startup currents higher than the overcurrent 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 overcurrent recovery bit. If this bit is set, the device automatically switches

the outputs on again after a programmable recovery time. The duty cycle in overcurrent

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

3kHz.

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 the light bulbs by setting the overcurrent recovery bit for the

first 50 ms. After clearing the recovery bit, the output is automatically switched off, if the

overload condition remains.

Figure 6.

Example of programmable soft start function for inductive loads

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