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UCG28828: Disable and Enable the Converter

Keith Keller
Expert 7580 points

Part Number: UCG28828

Hello,

We are designing with the UCG28828 and would like to enable / disable the IC from the secondary side through an opto coupler. 

  • Is FLT pin the best way to disable the IC?
  • Will auto-retry will occur when FLT is pulled low?
  • Would using FB pin be a secondary option, becuase there would be no soft-start when enabled?

Thank you, Keith

  • 0
    TI__Expert 4525 points

    Hi Keith, 

    Keith Keller said:
    We are designing with the UCG28828 and would like to enable / disable the IC from the secondary side through an opto coupler. 

    May I know more details about your application?

    Keith Keller said:
    • Is FLT pin the best way to disable the IC?
    • Will auto-retry will occur when FLT is pulled low?

    Yes, FLT pin is the best way to disable the IC as by pulling FLT pin voltage below 0.6V, it will be considered as external over temperature fault. And to check for the external overtemperature fault, a 75μA current is sourced from the FLT pin through the external resistor to ground. This current is sourced for a 250μs on-time during every 10ms time period. An up-down counter increments every time when VFLT is lower than 0.6V (typically) with the sourced current. This counter decrements when VFLT is higher than 0.6V (typically) during the 250μs duration. An external overtemperature fault is declared at a count of three and based upon FCL pin setting device will do auto-retry or latched. 

    Keith Keller said:
    Would using FB pin be a secondary option, becuase there would be no soft-start when enabled?

    Yes, alternative is to work with FB pin to enable/disable device. But before I recommend any solution here, could you please help me to understand your requirement clearly - like what is test condition when you want device to enable and disable it? When device is disable, then at same test condition you want device to go in latched or auto-retry mode? What is External OTP & OVP protection demand, is it latched or auto-retry?

    Also, regarding soft-start- 

    If Vfb < 0.25V to disable and on-release once Vfb goes higher than 0.3V, it will operate in burst mode. No-soft start on enable. 

    If Vfb pulled up to its open feedback voltage, device will go into OFB faults and based upon FCL pin setting it will decide either latched or auto-retry conditions.

    Thanks

    Regards

    Anita

  • 0
    TI__Expert 7580 points

    Hi Anita,

    This is a 120Vac to USB-C 120W solution.,

    We want to disable the solution through an optocoupler and it needs to be able to recover without power cycling the IC (no latching). 

    We want the converter to start with soft-start enabled

    What is the best way to do this? 

    Thank you, Keith

  • 0 in reply to Keith Keller
    TI__Expert 4525 points

    Hi Keith, 

    Thanks for input. As mentioned above, device can be enabled or disabled using discrete circuit at FLT pin by pulling below 0.6V. As the customer requirement is to have soft-start enabled which means auto-retry setting and that means even output OVP will also be auto-retry, is it acceptable to customer?

    Thanks

    Regards

    Anita