TA8428K/FG
2010-02-23
4
OVERCURRENT PROTECTION (ISD)
• Basic Operation
When output sink and source currents (TA8428K: at pins 3 and 5; TA8428FG: at pins 15 and 16) are equal to
or lower than the overcurrent threshold, output signals are controlled by input signals. However, when any of
these currents exceed the threshold, outputs are turned on and off periodically as shown in Figure 1.
Figure 1 Basic Operation
• Functional Description
The output current is sensed by monitoring the V
BE
voltage at each output transistor. The current sensor is
connected to each output transistor and to the ISD circuit. If a current higher than the overcurrent threshold
flows through any one of the four output transistors, the ISD circuit is activated. This circuit incorporates a
timer. If the overcurrent condition persists for 20 μs (typ.), the output is switched to a high-impedance state.
Then, it is turned back on after 80 μs (typ.). If the overcurrent condition still persists at this time, the ISD
circuit repeats this overcurrent protection sequence until the overcurrent condition is removed.
This circuit cannot protect the device from all types of over currents. If the outputs are short-circuited to
each other or to ground, the IC may be permanently damaged before the protection circuit is activated.
Therefore, a resistor or fuse should be connected in the supply voltage line.
