Galil DMC-2X00 - Manual (Page 236)

The resistor pack RPx3 limits the amount of current available to source, as well as affecting the low
level voltage at the I/O output. The maximum sink current is 2mA regardless of RPx3 or I/OC voltage,
determined by the NEC2505 optical isolator IC. The maximum source current is determined by
dividing the external power supply voltage by the resistor value of RPx3.
The high level voltage at the I/O output is equal to the external supply voltage at I/OC. However,
when the output transistor is on and conducting current, the low level output voltage is determined by
three factors. The external supply voltage, the resistor pack RPx3 value, and the current sinking limit
of the NEC2505 all determine the low level voltage. The sink current available from the NEC2505 is
between 0 and 2mA. Therefore, the maximum voltage drop across RPx3 is calculated by multiplying
the 2mA maximum current times the resistor value of RPx3. For example, if a 10k ohm resistor pack
is used for RPx3, then the maximum voltage drop is 20 volts. The digital output will never drop below
the voltage at OUTC, however. Therefore a 10 k
Ω resistor pack will result in a low level voltage of
0.7 to 1.0 volts at the I/O output for an external supply voltage between 4 and 21 VDC. If a supply
voltage greater than 21 VDC is used, a higher value resistor pack will be required.
Output Command Result
CB
n
V
out
= GND
iso
SB
n
V
out
= V
iso
The resistor pack RPx3 is removed to provide open collector outputs. The same calculation for
maximum source current and low level voltage applies as in the above circuit. The maximum sink
current is determined by the NEC2505, and is approximately 2mA.
Open Collector
1/4 NEC2505
To DMC-2x40 +5V
DMC-2x40 I/O
I/O
n
OUTC
n
1/8 RPx2
Figure A-14
Electrical Specifications
• I/O points, configurable as inputs or outputs in groups of 8
Digital Inputs
• Maximum voltage: 28 VDC
• Minimum input voltage: 4 VDC
• Maximum input current: 3 mA
226
• Appendices
DMC-2X00