I am planning to use the ADUM140E to convert 3.3V GPIO from an FPGA to 5V to interface with digital I/O on a servo drive. The servo drive DIO are active low and use opto-isolators with 50mA max drive. I have a couple of questions about the iCoupler:
Is there a better iCoupler part to use for this type of application? I don't really need the 150Mbps throughput of the ADUM140E series; my outputs are pretty much DC GPIO.
The ADuM140E is rated for 4mA outputs. It does not have output short circuit protection and you would need to and some limiting resistance to the output to protect it in case of a short circuit.
The part number ADuM1421 does not come up in a google search. The part number ADuM1420 does, and has outputs of 12 to 15 V with peak current of 0.1A for 1 sec max. But, the ADuM1420 is not recommended for new designs.
It may be that you need to add a buffer at the output of the digital isolator to provide the 50mA max source or sink current.
If the opto-isolators already provide the isolation you need, it could be what you need is level translation from 3.3V to 5V, with 5V output drive source/sink. You may want to consider a 4 channel analog switch like the ADG1611, with a max of 63mA at 125C in the TSSOP package. We have another group at Analog Devices that can help support detailed questions on analog switches.