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L9733

Fault operation

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

fault is written in the fault register. If the switching OFF protection is not active the On

phase overcurrent protection is a linear current limitation and no diagnosis is available.

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 power MOS transient, after a switching-off command, is longer than Tdel

filtering time, a bad diagnostic behavior happens and software filtering may be

needed.

7.2

High-side configured output fault operation

The diagnostic circuitry verifies for the high-side configured output the following condition:

Normal operation, open load, short circuit to Vbat and overcurrent (only if the switching OFF

protection, selectable for each channel via SPI bus, is active).

The diagnostic circuitry operates in two different modes, selected for each channel by SPI:

no latch mode and latch mode. The fault priority is overcurrent and then open load or short

circuit to Vb, this means that if an overcurrent occurs the fault register is always overwritten

and following open load or short to Vbat faults that happen before that the register is cleared

will be ignored.

7.2.1

No latch mode

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

1.

Open load

The diagnostic of open load is detected only in OFF condition sensing the Src1-8

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.

2.

Short Circuit to Vb

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

Src1-8 output voltage. This fault is detected on the falling edge of the CS input if the

power drain voltage is higher than the Vth_Vbat threshold.

3.

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