L9347

Functional Description

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The output current is measured during the recirculation of the load. The current sense

resistor is in series to the free wheeling diode. If this recirculation path is interrupted the

regulator stops immediately and the status output remains low for the rest of the input cycle.

The output period is 64 times the clock period. With a clock frequency of 250kHz the output

PWM frequency is 3.9kHz. The output PWM is synchronized with the first negative edge of

the input signal. After that the output and the input are asynchronous. The first period is

used to measure the current. This means the first turn-on of the power is 256

s after the first

negative edge of the input signal.

As regulator a digital PI-regulator with the Transfer function for:

KI:

and KP: 0.96

for a sampling time of 256

s is realised.

To speed up the current settling time the regulator output is locked to 90% output PWM untill

the target current value is reached. This happens alsowhen the target current value

changes and the output PWM reaches 90% during the regulation. The status output gets

low if the target current value is not reached within the regulation error delay time of

tRE=10ms. The output PWM is than out of the regulation range from 10% to 90%.

3.5

Protective circuits

The outputs are protected against current overload, overtemperature, and power-GND-loss.

The external clock is monitored by a clock watchdog. This clock watchdog detects a minimal

frequency f

CLK,min and wrong clock duty cycles. The allowed clock duty cycle range is 45% to

55%. The current-regulator stages are protected against recirculation errors, when D3 or D4

is not connected. All these error conditions shut off the power stage and invert the status

output information.

3.6

Error detection

The status outputs indicate the switching state under normal conditions (status LOW = OFF;

status HIGH = ON). If an error occurs, the logic level of the status output is inverted, as listed

in the diagnostic table below. All external errors, for example open load, are filtered

internally. The following table shows the detected errors, the filter times and the detection

mode (on/off).

0.126

z1

–

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