iCoupler clamp current

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:

  • What is the maximum output drive, source and sink?
  • Are the outputs internally current limited? For instance, if someone accidentally shorts an output pin to 5V while the output is ON, would the part get damaged?

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.

  • I did some more research, and I think the ADUM1421 will work for me; it's a bit overkill for my application, but it seems to have all the features I'm looking for. Still open to other suggestions from though.

  • 0
    •  Analog Employees 
    on Jan 22, 2017 10:52 PM

    Hi Kiy,

    I'm an applications engineer for Switches and Multiplexers.

    How may I be able to help you?

    Best Regards,

    May 

  • 0
    •  Analog Employees 
    on Jan 22, 2017 11:43 PM

    Hi

    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. 

    Regards, Brian

  • Brian

    Thanks for your response. I meant to say ADUM4121 instead of ADUM1421.

    The opto-isolators in the drive provide isolation between the drive's internal high voltage electronics and the low voltage (5V) digital interface to my micro-controller. My micro-controller runs on 3.3V logic, and I wanted to also isolate it from the drive's circuits just to be safe.

    I like your suggestions to use something like the ADG1611 switch; it would allow me to use the same components for inputs and outputs, and it meets my output drive requirements. I can use a series resistor to current limit the switches that drive outputs. If you can refer me to someone I can talk to about your analog switches, that would be great!

    Regards,

    Kiy

  • 0
    •  Analog Employees 
    on Feb 7, 2017 6:02 PM

    Hi Kiy,

    Yes, analog switches have ESD protection diodes.

    As seen in the figure below, in a standard analog switch circuit the source, drain, and logic terminals include clamping diodes to the supplies to provide ESD protection. Reverse-biased in normal operation, the diodes do not pass current unless the signal exceeds the supply voltage.

    This is further discussed in the article:

    Ask The Applications Engineer-40 Switch and Multiplexer Design Consideration for Hostile Environments by Michael Manning

    Let me know if this helps.

    Best Regards,

    May