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ISOW7841: Can ISO784x or ISOW784x be used as level transformer? i.e., from 3.3V LVCMOS to 5V CMOS?

Part Number: ISOW7841

Hi, I want to use an FPGA to control external logics, the VCCIO at FPGA is 3.3V and the level at the device is 5V. Can I use ISO784x or ISOW784x as level transformers (shift)? i.e., The outputs of FPGA are directly connect to ISOW784x or ISO784x, and set VCC=5V, VISO=5V, so that the level at the isolation side is 5V CMOS? Thanks!
  • Hi,

    I understand that the requirement is to connect the FPGA IO lines operating at 3.3V directly to digital lines of the isolator operating at 5V. Depending on the threshold levels, this may or may not work.
    From the perspective of the isolator, there shouldn't be any problems as long as the high and low thresholds are met.
    But from the perspective of FPGA, please check whether it is ok to apply 5V to the 3.3V IO lines of the FPGA and also whether the thresholds levels are ok for reliable communication.

    Another option is to use a digital isolator which doesn't have integrated power (like ISO784x or ISO774x) and operate the side of the isolator interfacing directly with the FPGA at 3.3V and the other side of the isolator at 5V.
    This above option can also be possible with an ISOW784x device (isolator with integrated power) under certain conditions.

    If above explanation is unclear, could you please share a diagram of the connections required between the FPGA and the isolator?
    If we continue the discussion with respect to a connection diagram we can have more clarity.

    Anand Reghunathan
  • In reply to Anand Reghunathan:

    Hi, Thanks for your reply. My VCCIO of FPGA is 3.3V. Previously, I firstly needed to transfer the control signals up to 5V, to then using opto-coupler to isolate the output. Or the input signals are received using opto-coupler, and then the logic are transfer downto 3.3V before connect to the FPGA. BTW, How could I attach images?
  • In reply to byliu:


    Is it necessary to operate the digital isolator at 5V?
    Digital isolators such as ISO7841 and ISO7741 or even ISOW7841 (with integrated power) are capable of functioning using 3.3V supply voltage.
    If 3.3V supply is provided to the isolator the FPGA can be directly interfaced with the IC with no issues. In such scenario no level transfer will be required.

    To attach images to the E2E post please click on "Use rich formatting".

    Anand Reghunathan