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L9825
Figure 2.
Output Control register structure
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 1 to 6 (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 7 and 8 (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
The output voltage at all outputs is compared with the diagnostic threshold, typ 0.38 · V
CC
.
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.
Table 2. Diagnostic 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-
ceeded the diagnostics threshold due to overcurrent, the output overload latch was set and the output has been
switched off. The diagnostic bit is low.
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)
Q2 Q4 Q6 Q8 Q1 Q3 Q5 Q7
MSB LSB
Control-bit output 7
Control-bit output 5
Control-bit output 3
Control-bit output 1
Control-bit output 8
Control-bit output 6
Control-bit output 4
Control-bit output 2
