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Original question:

ISOW7841: Isolated output problem

ISOW7841: VISO out problem

Dagmar Carnier Neto
Prodigy 20 points
Part Number: ISOW7841

I´m testing a new ISOW7841 IC, and have problems with VISO out right away. 

Supplying 5V to VCC directly from a power supply, SEL pin connected to VISO, just give me 0.6V out at VISO (should be 5V). Current consuming indication  is 0.00A at the power supply display.

When I put a 4.7uF electrolytic cap between VCC and GND, current consumption rise to 0.2A, and VISO goes to 2.95V.

I found all  this very strange, since following the datasheet does´nt seem to point any further recommendation concerning VCC supply.

The IC is directly soldered to a SOP adapter and plugged in a prototyping board.

Could you please pont me any directions?

Thanks, best regards,

Dagmar

  • 0
    TI__Genius 17100 points

    Hi Dagmar,

    Thank you for posting to E2E!

    I'm sorry to hear you are having trouble with ISOW7841, this behavior is definitely strange. I have a few comments and questions that may help us figure out what is going wrong here:

    1. It is necessary for both Vcc and Viso to have decoupling capacitors connected to their respective grounds. Are decoupling capacitors connected from VISO to GND2 (isolated ground)?
    2. Is there anything else connected to VISO other than SEL? What is the expected current load on this pin?
    3. Could you temporarily disconnect SEL and see if Viso behavior is any different?
    4. Please verify that all pins are soldered and connected correctly and there are no shorts to either GND, Vsupply, or Viso. Ensure both connections to GND1 on side 1 (pin 2 and pin 8) are connected and both connections to GND 2 on side 2 (pin 15 and pin 9) are also connected. 

    If you can share them, feel free to post a schematic or PCB layout image for analysis, and if you'd like to keep them private, please send me a Request to Connect. To maximize performance from the ISOW7841, you may refer to this Application Report.

    I will await your response!



    Respectfully,
    Manuel Chavez

  • 0 in reply to Manuel Chavez
    Prodigy 20 points

    Hello Manuel,

    Solved. Definitively was the lack of decoupling at the VISO side. Everything seems work OK now!

    Thanks for the prompt reply,

    Dagmar

  • 0 in reply to Dagmar Carnier Neto
    TI__Genius 17100 points

    Dagmar,

    We're happy to help! Please feel free to post again with any other questions if needed.


    Best wishes,
    Manuel Chavez