L99DZ80EPTR datasheet(35/68 Pages) STMICROELECTRONICS

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L99DZ80EP

Application information

one PWM counter each. Therefore the maximum on-time is 100% - 1 LSB.

1 LSB = 100/128 %. Which output uses which corresponding PWM driver can be seen in

the SPI register definition. When programming a specific duty-cycle, the output on/off times

as well as the slopes must be taken into account.

3.13

Cross-current protection

The six half-brides of the device are crosscurrent 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 crosscurrent protection time. After the crosscurrent 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

3.14

Programmable soft-start function to drive loads with higher

inrush current

Loads with start-up 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 softstart 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

3 kHz. 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 overload

detection the microcontroller can switch on the light bulbs by setting the overcurrent

recovery bit for the first e.g. 50 ms. After clearing the recovery bit the output is automatically

switched off, if the overload condition remains. This overcurrent detection procedure has to

be followed in order to 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.

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