Functional description

L9823

14/19

DocID7791 Rev 7

3.3

Diagnostics

The output voltage at all outputs is compared with the diagnostic threshold, typ 0,55

Fault condition 1

Output short circuit to Vbat:



For SFPD = Low the output was switched on and the voltage at the output exceeded

the diagnostics threshold due to overcurrent, the output overload latch was set and the

output has been switched off. The diagnostic bit is high.



For SFPD = high the output was switched on and the voltage at the output exceeds the

diagnostics threshold. The output operates in current regulation mode or has been

switched off due to thermal shutdown. The status bit is high.

Fault condition 2

Open load or output short circuit to GND:



The output is switched off and the voltage at the output drops below the diagnostics

threshold, because the load current is lower than the output diagnostic current source,

the load is interrupted. The diagnostic bit is low.



At the falling edge of CSB the output status data are transferred to the shift register.

When SCB is low, data bits contained in the shift register are transferred to SO output

at every rising SCLK edge.

Figure 5. Pulse diagram to read the outputs status register

Table 7. Diagnostic for outputs

Output

Output voltage

Status bit

Output mode

off

> DG-threshold

high

correct operation

off

< DG-threshold

low

fault condition 2)

on

< DG-threshold

low

correct operation

on

> DG-threshold

high

fault condition 1)