Galil DMC-2X00 user manual Digital Inputs, Figure A-14

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 kΩ resistor pack will result in a low level voltage of

0.7to 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
CBn	Vout = GNDiso
SBn	Vout = Viso

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

To DMC-2x40 +5V

1/8 RPx2

DMC-2x40 I/O

Figure A-14

1/4 NEC2505

I/On

OUTCn

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

DMC-2X00 Appendices y 181