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Power outputs characteristics

for flyback current, outputs short circuit protection and diagnostics

For output currents flowing into the circuit the output voltages are limited. The typical value of this voltage is 50V.

This function allows that the flyback current of a inductive load recirculates into the circuit; the flyback energy is

absorbed in the chip.

Output short circuit protection for outputs 3 to 8 (dedicated for loads without inrush current): when the output

current exceeds the short circuit threshold, the corresponding output overload latch is set and the output is

switched off immediately.

Output short circuit protection for outputs 1 and 2 (dedicated for loads with inrush current, as lamps): when the

load current would exceed the short circuit limit value, the corresponding output goes in a current regulation

mode. The output current is determined by the output characteristics and the output voltage depends on the

load resistance. In this mode high power is dissipated in the output transistor and its temperature increases rap-

idly. When the power transistor temperature exceeds the thermal shutdown threshold, the overload latch is set

and the corresponding output switched off.

For the load diagnostic in output off condition each output features a diagnostic current sink, typ 60µA.

Diagnostics

Outputs 1 and 2 features dedicated fault latches. The output status signal is filtered and latched. The fault latch-

es are cleared during NCS low. The latch stores the status bit, so the first reading after the error occurred might

be wrong. The second reading is right.

Diagnostic Table for outputs 1 and 2 in parallel controlled mode:

Fault condition 1) "output short circuit to Vbat" : the output was switched on and the voltage at the output ex-

ceeds the diagnostics threshold. The output operates in current regulation mode or has been switched off due

to thermal shutdown. The status bit is low.

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 cur-

rent source, the load is interrupted. The diagnostic bit is low.

For outputs 3 to 8 the output status signals, are fed directly to the SPI register.

Diagnostic Table for outputs 1 to 8 in SPI controlled mode:

Output 1, 2

Output-voltage

Status-bit

Output-mode

off

> DG-threshold

high

correct operation

off

< DG-threshold

low

fault condition 2)

on

< DG-threshold

high

correct operation

on

> DG-threshold

low

fault condition 1)

Output 1 ... 8

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)