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ISO1212: ISO1212 not working as expected

Chris Henschel
Intellectual 385 points
Part Number: ISO1212

Tool/software:

Hi,

On a new design I used the ISO1212 for DI. I copied the reference design as shown below: 

Rthr is 1k and Rsens is 562 Ohm

I measure a current of about 20mA as soon as I apply 24V on the Rthr input. The device output is not switching and stays at 0V. The Voltage on the Sense Pin is 7V therefore we have about 17mA of current inside RTHR. (24-7)/1k 

Any suggestion why my ISO1212 needs that much current?

I also measured a second PCB with the same result.

Thanks for your answers!

Cheers,

Chris

  • 0
    TI__Mastermind 22545 points

    Hello Chris, 

    Thank you for reaching out. I would expect the ISO1212 to limit the current to the ~2.25mA as shown in 6.9 Electrical Characteristics. Has something happened while testing that could damage the ISO1212? Would you be able to share a schematic?

    Best,
    Andrew

  • 0 in reply to Andrew J
    Intellectual 385 points

    Thanks for your response. I received the new ISO1212 chip from DigiKey and replaced it, ensuring the orientation was correct. Unfortunately, I still got the same result.

    I also tried removing the Rthr resistor, and the IC started switching correctly when a 24V input was applied. However, it then consumed around 100mA, which is obviously far too high. Anyhow I think the IC is working.


    please find the schematic below: 

    I switch the In1 to 24V (in respect to the system GND - Isolation not needed here). The Outputs are left opened - I check them with a Multimeter.

    Thanks in advance

  • 0 in reply to Chris Henschel
    TI__Mastermind 22545 points

    Hello Chris, 

    Thank you for the added details. I agree the device seems to be okay and should operate as normal based on the schematic. Looking at the first post again I have a few comments that I gathered from the team.

    • I am assuming customer is measuring 7V on SENSE pin with respect to FGND, which is expected.
      • Please measure voltage across RSENSE, this should be 1.25V. If it is, then device is working normal.
    • Would it be possible to see the complete board schematic? It is possible that other components on PCB are consuming current.
    • You could also test by disconnecting the ISO1212 from other components and power only ISO1212 and test. Or alternatively, order and test on an EVM.

    Best,
    Andrew