NI UMI-7774/72 User Guide and Specifications
32
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The Digital output circuit sources current to external loads. The maximum output current for the digital
outputs depends on the V
iso
voltage. Refer to Table 4 for the maximum output current at different V
iso
voltages.
Note
If the load current exceeds the over current trip point, the output shuts off.
The output voltage is within 1.2 V of the voltage provided on the V
iso
power supply. Refer to Figure 27
for an illustration of the Digital output interface circuit.
To cause current to flow through the digital inputs, the voltage applied to the digital inputs must be
greater than 3.5 V and less than 30 V. Also, the source must be able to provide at least 7.2 mA to turn
on the optical isolator and result in an ON condition. When the applied voltage is below 2 V, the input
results in an OFF condition.
Figure 27.
UMI-7774/72 Optically Isolated Sourcing Digital Output Interface Circuit and Connection to an
External Load
Table 10.
Maximum Available Output Current
V
iso
Maximum Output Current (mA)
30 V
160 mA
24 V
150 mA
5 V
60 mA
Digital
Output
Viso
Ciso
Vcc
Load
Current Limiter
Current
Sense
UMI-7774/72
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