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ISOW7841: Large Ripple and Sagging Voltage

Ryan.Bishop
Expert 3900 points
Part Number: ISOW7841

Hello,

I am working with a customer on their ISOW7841 design and we are seeing extremely large voltage ripple on the Viso output rail.

Figure 30 of the datasheet shows that Vpp should be less than 100mV at 5V full load.

In testing, the customer has 10uF on Viso and using a dummy load of 4.7kOhm or 120Ohm. See scope-shots below for the ripple they are seeing under both conditions. Note that both waveforms are averaging under 5V.

4.7kOhm:

 

120Ohm:

Let me know what steps we can take to narrow in on the issue here.

Thank you!
Ryan B.

  • 0
    TI__Mastermind 49445 points
    Hi Ryan,

    Thank you for sharing details about the customer issue along with waveform. I see that the ripple is abnormally very high which is not expected out of ISOW7841 with 10µF cap and 120Ω. Please note that decoupling capacitor placement and routing also plays a role in the effectiveness of the decoupling capacitor. I would like to look at the schematic and PCB layout, please allow me to reach out to you over email for the same. Thanks.


    Regards,
    Koteshwar Rao