L9352B

Functional description

15/27

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 256µs is realized.

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

the target current value is reached. This happens also when 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

t

RE=10ms.

4.5

Protective circuits

The outputs are protected against current overload, over temperature, 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.

4.6

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

–

---------------

Table 7.

Error detection

ON State

EN &IN = HIGH

OFF State

EN &IN = LOW

Filter time

Reset done by

Short circuit of the load

X

tsf

EN & IN = “LOW”

for TD or TDreg

Open load

(under voltage detection)

Xtlf

timer TD

Open load

(under current detection)

Xtsf

timer TD

Overtemperature

X

tsf

EN & IN = “LOW”

for TD or TDreg

Power-GND-loss

X

X

tlf

in on: EN & IN = “LOW”

for TD or TDreg

in off: timer TD

Signal-GND-loss

X

X

tlf

timer TD