L9733 datasheet(26/35 Pages) STMICROELECTRONICS

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Fault operation

L9733

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DocID11319 Rev 12

7.1.1

No latch mode

This diagnostic operating mode doesn't latch open load and short to GND faults.

Open load

The diagnostic of open load is detected only in OFF condition sensing the Drn1-8

output voltage. This fault is detected on the falling edge of the CS input if the power

drain voltage is inside the voltage range limited by the two thresholds Vth_Vbat and

Vth_GND. An internal current limited voltage regulator fixes the drain voltage inside the

described range when no load is connected.

Short circuit to GND

The diagnostic of short circuit to GND is detected only in OFF condition sensing the

Drn1-8 output voltage. This fault is detected on the falling edge of the CS input if the

power drain voltage is lower than the Vth_GND threshold.

Overcurrent

The diagnostic of overcurrent is detected only in ON condition, if the switching OFF

protection of the channel is enabled (default), sensing the current level of the output

power transistor. If the output current has been above the short threshold Iovc for the

filtering time Tdel the output power is switched off and at the same time an overcurrent

fault is written in the fault register.

There are three possibilities to restart one output after the fault has occurred:

–

Automatically after a time Tres

–

On the rising edge of CS if two valid DI bytes have been received and first the

Output Status in the command register is written with logic '0' and then with a logic

“1” in the following SPI cycle

–

On the rising edge (low to high transition) at the corresponding parallel input pin

(only for Outputs 6-8).

–

If the switching OFF protection is not active the On phase overcurrent protection is

a linear current limitation and no diagnosis is available.

The use of the IN6-8 pins for PWM control on the outputs 6-8 could generate bad diagnostic

behavior when the falling edge of CS happens a short time after the falling edge of IN6-8

during the power MOS transient. Software filtering may be needed to ignore fault signals

during Drn6-8 transient after falling edge of IN6-8.

7.1.2

Latch mode

This diagnostic operating mode latches all faults when they happen.

Open load

The diagnostic of open load is detected only in OFF condition sensing the Drn1-8

output voltage. This fault is detected if the power drain voltage is inside the voltage

range limited by the two thresholds Vth_Vbat and Vth_GND for the filtering time Tfilt.

An internal current limited voltage regulator fixes the drain voltage inside the described

range when no load is connected.

Short circuit to GND

The diagnostic of short circuit to GND is detected only in OFF condition sensing the

Drn1-8 output voltage. This fault is detected if the power drain voltage is lower than the

Vth_GND threshold for the filtering time Tfilt.

Overcurrent

The diagnostic of overcurrent is detected only in ON condition, if the switching OFF

protection of the channel is enabled (default), sensing the current level of the output

power transistor. If the output current has been above the short threshold Iovc for the

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