L99MOD50XP datasheet(23/42 Pages) STMICROELECTRONICS

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DS12615 Rev 4

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L99MOD50XP

Application information

3.10

Over-load detection

In case of an over-current condition a flag is set in the status register in the same way as

during open load detection. If the over-current signal is valid for at least tISC(typ) = 55 μs,

the over-current flag is set and the corresponding driver is switched off to reduce the power

dissipation and to protect the integrated circuit. If the over-current recovery bit of the output

is zero, the microcontroller has to clear the status bits to reactivate the corresponding driver.

3.11

Current monitor

The current monitor output sources a current image at the current monitor output which has

two fixed ratios of the instantaneous current of the selected high-side driver. Outputs with a

resistance of 500 mΩ and higher have a ratio of 1/2000 and those with a lower resistance of

1/10000. The signal at output CM is blanked after switching on the driver until correct

settlement of the circuitry (at least for 64 μs). The bits 0 to 3 of the control register 3 define

which of the outputs are multiplexed to the current monitor output CM/PWM2. The current

monitor output allows a more precise analysis of the actual state of the load rather than the

detection of an open- or overload condition. For example it can be used to detect the motor

state (starting, free-running, stalled). Moreover, it is possible to control the power of the

defroster more precisely by measuring the load current. The current monitor output is

bidirectional (PWM inputs).

3.12

PWM inputs

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

interface. If the PWM enable bit is set in control registers 2 or 3, the output is controlled by

the logically AND-combination of the PWM signal and the output control bit in Control

Registers 0 and 1. The outputs OUT1-4, 6, 7, 9, OUT11 are controlled by the PWM1 input

and the outputs OUT5, 8 and OUT10 are controlled by the bidirectional input CM/PMW2.

For example, the two PWM inputs can be used to dim two lamps independently by external

PWM signals. In case of switching off a high/low side switch in PWM mode a minimum off

time of appr. (256 μs – tdon+ tdoff) is predefined by the state machine, to avoid switching on

the high/low side again during the negative slope. For a PWM frequency of 100Hz this

means the maximum duty cycle is about 98%. Larger duty cycles can be realized by

applying pulse skipping.

3.13

Cross-current protection

The six 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.

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