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Original question:

TPS2121: Operation of seamless switch between inputs

TPS2121: application mode "Manual switchover" question

Will Wang47
Expert 7780 points
Part Number: TPS2121

Hi Team,

Customer want use TPS2121 "manual switchover" mode, they use MCU GPIO control the part CP2, and they need the fast switch feature to reduce the voltage dip at output. Experiment performed on TPS2121 EVM, find the following request:

  1. EVM Vin1 = 5V, Vin2 = 4V; PR1 = EVM 3.3V connector operation(high) install jumper J1; CP2 control by GPIO; Output current = 2.5A;

    Configuration follow datasheet TPS2121 manual switchover, but it shows large dip, ~ 125us, doesn't get result as datasheet mentioned 5us fast switch. Could you help check about this? 

Thanks and best regards,

Will

  • 0
    TI__Genius 10652 points

    Hi Will, 

    Fast switchover is only enabled when CP2 voltage is > VREF (~1.07V). Because of this, you need to ensure the "LOW" CP2 voltage is still above VREF. Because your CP2 voltage goes all the way to ground is the reason why the device can't use fast switchover.

    There a few ways to ensure this condition is met on CP2. An alternative is to keep CP2 fixed > 1.07V (vref) and drive PR1 pin with MCU GPIO which will avoid the issue you are having. 

    Please let me know if any other questions on this. If this answers your question, please let me know by pressing the green button. 

    Best

    Dimitri

  • 0 in reply to dimitri james
    TI__Expert 7780 points

    Hi Dimitri,

    Thanks for your suggestion. Follow your guide, I did the following experiment using TPS2121 EVM setup, does the result aligned with expected?

    1. Vin1 = 5V, Vin2 = 4V; CP2 = EVM 3.3V connector operation(high); PR1 control by GPIO; Output current = 2.5A;

    Thanks and Best Regards,

    Will

  • 0 in reply to Will Wang47
    TI__Genius 10652 points

    Will,

    I made an error in my previous response. 

    BOTH PR1 and CP2 voltages must be >VREF~=1.07V in order for fast switchover to occur.

    therefore, whether or not toggling PR1/CP2 you msut ensure the LOW level of either still is above the Vref voltage. 

    Best

    Dimitri