L99DZ70XP datasheet(27/47 Pages) STMICROELECTRONICS

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L99DZ70XP

Application information

Doc ID 15162 Rev 3

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3.13

Cross-current protection

The six 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 is changed to a

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

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

before the opposite driver starts to conduct.

3.14

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 softstart function (i.e. overcurrent recovery mode). Each driver has a

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

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

condition can be programmed by the SPI interface to 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 1.7kHz

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. For over-load

detection the microcontroller can switch on the light bulbs by setting the over-current

recovery bit for the first e.g. 50ms. After clearing the recovery bit the output will be

automatically switched off, if the overload condition remains. This over-load detection

procedure has to be followed in order make it possible to switch on the low-side driver of a

bridge output, if the associated high-side driver has been used in recovery mode before.

Figure 9.

Example of programmable soft-start function for inductive loads

L99DZ70XP Datasheet(PDF) 27 Page - STMicroelectronics