L9951XP datasheet(21/36 Pages) STMICROELECTRONICS

21 / 36 page

L9951 / L9951XP

Application information

Doc ID 14173 Rev 8

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3.10

PWM input

Each driver has a corresponding PWM enable bit which can be programmed by the SPI

interface. If the PWM enable bit is set, the outputs OUT1 to OUT5 are controlled by the

logically AND-combination of the signal applied to the PWM input and the output control bit

in input data register1.

3.11

Cross-current protection

The three half-brides 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

will be 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 will be 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 totally turned-off

before the opposite driver will start to conduct.

3.12

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 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 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

L9951XP Datasheet(PDF) 21 Page - STMicroelectronics