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TPS23755EVM-894: 12V Adapter Priority and Smooth Transition

Nicholas Carley
Expert 8355 points
Part Number: TPS23755EVM-894

Hello,

I don't see any information in the User's Guide about how this circuit helps with a smooth transition. I've tried recreating the circuit in Tina TI and the results are inconclusive on weather it from a transition perspective. The only thing from an adapter priory perspective seems to be the opto-coupler feedback to AUX-D.

Am I missing something?

Thanks,
Nick

  • 0
    TI__Mastermind 40145 points

    Hi Nicholas,

    I recommend looking at the datasheet instead that goes into detail on the AUX_D and AUX_V functionality to achieve smooth transition. 

    When an adapter is plugged in, the flyback output will drop to a voltage lower than the adapter such that adapter takes priority since it is essentially diode ORing together. Please let me know if this helps. Thanks!

  • 0 in reply to Darwin Fernandez
    TI__Expert 8355 points

    Hi Darwin,

    I've read through the Aux_D and Aux_V portions and that makes sense, the optocoupler circuitry and D8 for ORing.

    What I don't understand is the purpose of D5/Q1/D11 (+ passives). I put this circuit into TINA TI and all I can see it does is pull down the transformer output by ~50mV. If the optocoupler feedback into Aux_D is handling the adapter priority and the D8 diode is handling the ORing, what is the purpose of these other components?

    Update: I realized I didn't include the image.


    Thanks,
    Nick

  • 0 in reply to Nicholas Carley
    TI__Intellectual 1005 points

    Nick, 

    Darwin is out on business travel so I am filling in for him. The purpose of this extra circuitry is to add a "dummy load" to the PoE input when the auxilary is plugged in. Keep in mind that the PSE will disconnect a PD if the load is below 10mA (on ~50V input).  

    The RC's control the timing to avoid glitches during the transition. 

    -Artem