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ISOW7844: The output voltage obtained through isolation is too high.

qiji LI
Prodigy 10 points
Part Number: ISOW7844

Hello Support team,

The isolation circuit I designed is used to collect whether the keys are grounded.  I have a 3.3V input and a 3.3V output, but when I measured the voltage at the output end, it was as high as 7V.  I don't understand the reason。

  • 0
    TI__Mastermind 24405 points

    已经收到了您的案例，调查需要些时间，感谢您的耐心等待。

  • 0
    TI__Mastermind 37140 points

    Thanks for the schematics. I am also not 100% sure why 7V would appear but have following suspicions for which I have some suggestions for you to implement and check

    1. VCC/VISO Supply Decaps:
      1. I don't see any supply decaps in the schematics - At least 0.1uF+10uF Capacitors are needed on both side near to the pins for working if device.
    2. Primary side VCC 3.3V supply current limits:
      1. If the current are limited and not able to supply the demanded current, device might not be able to regulate the voltage
      2. Check 3.3V supply current limits for both U8 and U11  - each of them should have 300mA current providing capability for transient current demands by internal DC/DC converter.
    3. Pull up resistor connected to VISO:
      1. Can you remove these pull resistors for your testing and then check for the VISO:
      2. If in case of grounding on INx lines, the current demand from VISO might be increasing making it out of regulation.