FP-DO-410
4
www.natinst.com
only a small leakage current to flow. Choose the impedance of the
loads driven by the output channels so that the current supplied
by any one channel in the ON state is no more than 1 A, and the
total current supplied by all channels at any one time is no more
than 8 A.
In the ON state, there is an effective resistance of 0.3
Ω
between
the output (V
out
) and the supply voltage (the V and V
sup
terminals).
This resistance causes a voltage drop between the external supply
voltage and the output voltage. For example, if the external supply
voltage is 5 V and the output current is 1 A, the output voltage is
4.7 V: [5 V – (1 A x 0.3
Ω
) = 4.7 V].
Figure 3 shows the diagram of one channel’s discrete output
circuit.
Figure 3.
Discrete Output Circuit
Overcurrent Protection
Detect an Overcurrent Condition
Each channel has an overcurrent protection circuit that monitors
the amount of current it sources to the V
out
terminal. If this current
exceeds a safe level, which is always at least 1 A, the output
automatically becomes deactivated. If the protection circuitry
disables an output that would otherwise be in the ON state, the
output state indicator for that channel remains lit, but the output
transistor is turned off. This condition also turns on the adjacent red
overcurrent state indicator and returns an overcurrent status to the
network module. To prevent false triggering, higher inrush currents
that exist for only a short time do not trigger the protection
circuitry.
COM
V
out
V
sup
V
C
Optical
Isolation
Load
