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L9950

3.7

Open Load Detection

The open load detection monitors the load current in each activated output stage. If the load current is

the status register. Due to mechanical/electrical inertia of typical loads a short activation of the outputs

(e.g. 3ms) can be used to test the open load status without changing the mechanical/electrical state of the

loads.

3.8

Over Load Detection

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

responding 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.

3.9

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. The bits 18 and 19 of the Input Data

Register 0 control which of the outputs OUT1, OUT4, OUT5, OUT6 and OUT11 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 de-

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

inputs).

3.10 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, the output is controlled by the logically AND-combination of the PWM signal and

the output control bit in Input Data Register. The outputs OUT1-OUT8 and OUT11 are controlled by the

PWM1 input and the outputs OUT9/10 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.

3.11 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 will be 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 totally turned-off before the opposite driver will start to conduct.

3.12 Programmable Softstart Function to drive loads with higher inrush currrent

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