17
9120A–AUTO–01/08
ATA6831/ATA6832 Driver ICs
8.
Overload Considerations
8.1
Driver Output Shorted to V
S
During normal operation ATA6831 is protected against short circuits by an overcurrent limitation.
However, some attention has to be paid to certain abnormal operating conditions that might
occur in practice. In particular, consider the case of an output shorted to V
out
while the IC is not
connected to supply voltage V
S
. Under these conditions, an unwanted backward current flows
from the shorted output via the voltage supply pin to the capacitor C1.
illustrates this
situation.
The backward current I
b
flows from OUTx via the HSx output stage to the VS pin until the capac-
itor C1 is charged to V
out
(minus drop across the diode). Its value is strongly influenced by the
capacitance of C1, but the quality of C1 (ESR) and any parasitic resistance can also have an
impact. The recommended range of C1 is 22 µF to 100 µF. As stated in the ATA6831 datasheet,
the maximum reverse current is 17A for a duration of 150 µs. The graph illustrated in
shows the typical voltage and reverse current gradients for a capacitor value of 100 µF.
Figure 8-1.
Current Flow in Case of OUTx Shorted to V
out
Figure 8-2.
Current and Voltage Gradients for V
out
= 16V, C1 = 100 µF; Channel 1 = I
b
,
Channel 2 = V
VS
, Channel 3 = V
out
V
out
V
S
C1
ATA6831
HSx
OUTx
I
b
