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ISOW1412: Abnormal Output High at RX Pin4

Francis Jiang
Expert 3250 points
Part Number: ISOW1412

Tool/software:

Hi Team,

Customer feedback that ISOW1412 will have an abnormal output high at RX Pin4, during the differential input is normal. The condition is under 5V power supply, and if it reduces to 4.53V, the abnormal high will not appear again.

I ask customer to check the Vdd and secondary side aux power output together, which is shown as below, it can be noticed that there is a big ripple wave, which causes this abnormal high at RX. The Visoout & Visoin are connecting to capacitors to GND. So there is no load at aux power. And for the 2kHz ripple wave, there is not any other 2kHz switching power in the system. Could you please help urgently check it, thanks.

Abnormal with 5V Vdd, CH1:RX, CH2: 5V Vdd, CH3: 485 differential input, CH4: 5V secondary side output

Normal with 4.53V Vdd:

BRs,

Francis

  • 0
    TI__Genius 17555 points

    Hello,

    Thanks for reaching out. 

    Our team is on TI Holiday. Please allow our team until Monday next week (4/21/2025) to reply.

    Regards,
    Aaditya V

  • +1
    TI__Expert 7585 points

    Hi Francis,

    Thanks for the details. Let me Clarify some of the points first

    1. The 2KHz frequency can be expected at VISOUT pin as it is the feedback control loop switching frequency of the internal DC-DC Converter

    Now Coming to the customer issue. I'm sorry but I'm unable understand what is the meaning of Abnormal HIGH from above inputs. The Only difference evident is the ripple on CH4(VISOUT).

    Inputs Needed:

    1. Schematics for ISOW1412
      1. Especially the Decoupling Capacitors on VISOUT and VISOIN Pins
    2. What is the ripple value on VISOUT that customer is suspecting as the main issue.
    3. Better RX Waveform for understanding the abnormality.
    4. Any Load Current Extracted from VISOUT pin in both scenario?

    Regards
    Varun

  • 0 in reply to Varun Kumar
    TI__Expert 3250 points

    Due to confidential message, please let me contact you offline, thanks.