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Problems with ISO124

Hossein Saberi
Prodigy 120 points
Other Parts Discussed in Thread: ISO124

Hi,

I am using the ISO124UE4 Precision Isolation Amplifier. I have designed and fabricated a board that get the data from sensors and send it to a processor. In order to isolate the input data lines and the processor I have used the ISO124. My problem is that they are getting hot when the board is working. The temperature goes high up to 45 degree Celsius. Is that normal or it should not be like that? Do you have any idea what have caused the high temperature? 

Thanks

  • 0
    TI__Guru**** 168485 points
    Hi Hossein,

    Welcome to our E2E forum! Under normal operating conditions, the ISO124 should not get hot. Can you share a schematic of how you have things hooked up?
  • 0 in reply to Tom Hendrick
    Prodigy 120 points

    Hi,

    The ISO124 IC is used as shown in the schematic. The Input signal is applied to VIN, +Vs1 and -Vs1 are connected to +12 and -12v and GND1 is the ground at the input side. +Vs2 and -Vs2 are supply voltage at the output side and connected to +12 and -12 and GND2 is the ground that are all isolated from the input side. Vo is the output signal that is scaled down usinga simple resistive division circuit. A Zener diode a used to limit the output voltage. In this configuration, the ISO124 IC gets hot up to 45 degree Celsius on the board. I was wondering what could be the reason and how I can solve this problem?

    Thanks

  • 0 in reply to Hossein Saberi
    TI__Guru**** 168485 points

    Hi Hossien,

    What is the input voltage? Two 22 ohm resistors for use as a voltage divider might be your problem here with the ISO124. You could easily be drawing quite a bit of current through the ISO124 with this setup.

  • 0 in reply to Tom Hendrick
    Prodigy 120 points
    Thanks for the response. The resistors are not 22 Ohms, they are 10 and 20K Ohm. Is there any other reason for this heat?

    Best,
    Hossein
  • 0 in reply to Hossein Saberi
    TI__Guru**** 168485 points
    Hi Hossein,

    Violating input common mode voltage limits perhaps, drawing too much power from the device, or perhaps a chip that got zapped by ESD... Are you using a proper PCB or is this a proto-type lab-board setup? Do you have a complete (and accurate) schematic to share? What you provided looks like R0603 and R0805 are both '22' (ohms was my assumption and now I suspect they are SMT sizes, not actual reference designations).