L9954 / L9954XP

Application information

Doc ID 14279 Rev 4

21/37

3.10

Current monitor

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

a fixed ratio (1/10000) of the instantaneous current of the selected highside driver. Signal at

output CM is blanked after switching on of driver until correct settlement of circuitry (at least

for 32 µs).

The bits 18 and 19 of the Input Data Register 0 control which of the outputs OUT1, OUT4,

OUT5 and OUT6 will be multiplexed to the current monitor output. 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 this can be used to detect the motor state

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

more precise by measuring the load current. The current monitor output is bidirectional (c.f.

PWM inputs).

3.11

PWM inputs

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

interface. If the PWM enable bit in Input Data Register 1 is set , the output is controlled by

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

Register 0. The outputs OUT1-OUT4 and OUT6 are controlled by the PWM1 input and the

output OUT5 is 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.

3.12

Cross-current protection

The three 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

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.