Fault Operation

L9733

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7

Fault Operation

The fault diagnostic capability consists of one internal 16 bits shift register and 2 bits are

used for each output. The diagnostic information are: no fault present, overcurrent, open

load and short circuit.

All of the faults will be cleared on the rising edge of Chip Select if a valid DI byte was

received

If all the bits b0-b15 of the fault register have value '1' it means that a thermal fault, at least

on one of the eight independent Outputs, occurred.

7.1

Low Side Configured Output Fault Operation

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

Normal operation, open load, short circuit to GND 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 GND, this means that if an overcurrent occurs the fault register is always

overwritten and following open load or short to GND faults that happen before that the

register is cleared will be ignored.

7.1.1

No latch mode

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

1.

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

Table 10.

Fault Register Definition

OUT 8

OUT 7

OUT6

OUT5

OUT4

OUT3

OUT2

OUT1

MSB

LSB

D1

D0

D1

D0

D1

D0

D1

D0

D1

D0

D1

D0

D1

D0

D1

D0

b15

b14

b13

b12

b11

b10

b9

b8

b7

b6

b5

b4

b3

b2

b1

b0

Table 11.

Fault Logic Definition

D1

D0

FAULT STATUS

0

0

No fault is present

0

1

Open load

1

0

Short circuit to GND (low side) or Short circuit to Vbat(high side)

1

1

Overcurrent