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ISOW7742-Q1: Changing VSEL At Runtime

nbetham
Prodigy 10 points
Part Number: ISOW7742-Q1

Tool/software:

Hi,

I'm working on integrating the ISOW7742-Q1 into a design and would like to have the ability to change the output voltage of the isolated power converter from 3V3 to 5V or vice versa at runtime. What is the behavior of the IC when VSEL is changed during operation? My through process was to use one of the forward channels to control VSEL pin while the converter is running to get the desired output voltage. Will the change in voltage, especially going from 5V to 3V3 damage the isolator?

Thanks!

  • 0
    TI__Genius 17475 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 7555 points

    Hi Neil,

    Thank You for reaching out. Please Find my inputs below:

    The VSEL pin needs to be shorted to VISOUT pin or GND2 pin only for 5V and 3.3V respectively. 

    Yes, you can change the connection of VSEL pin between VISOUT and GND2 or vice versa when the device is operational without any issue, this won't damage the isolator.

    • Just a heads up for a possible case scenario: Do take care of the External Load resistor(if connected) if you're switching from 3.3V to 5V and 3.3V is already operating with lowest resistor load(for full load of 140mA in 5V VDD and 3.3V VISOUT) on VISOUT pin, this will damage the internal power converter as 5V will draw more current than max rated 110mA

    Regards
    Varun

  • 0 in reply to Varun Kumar
    Prodigy 10 points

    Hi Varun,

    Thanks for the clarification!

  • +1 in reply to nbetham
    TI__Expert 7555 points

    Hi Neil,

    Update on this. I checked with our device experts afterwards and although there is no obvious failure in device but performance is not guaranteed across temperature and devices.

    Also when switching dynamically from 3.3V to 5V scenario, the soft start feature will not be available.

    Hence, Changing VSEL Dynamically is not a preferred operation mode and so my recommendation for your design is to go for STATIC only signals at VSEL during power up.

    Apologies for the Confusion here.

    Regards
    Varun

  • 0 in reply to Varun Kumar
    Prodigy 10 points

    Okay, understood. Thanks for the clarification.