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TPS23754

WhiteHorse
Genius 4430 points
Other Parts Discussed in Thread: TPS23754

Hi E2e,

Our customer has a question concerning the TPS23754.  They needed a 24V output solution. We gave them TI's TPS23754_EVM420_24V_TestReport.pdf reference design to copy. 

They have been drawing up the schematic for the TPS23754 with a 24V output.   Looking over the adapter input section they have a question.  They have gone through the equations for choosing the correct values of R17, R18, and R19 (under the PPD and APD sections) in the attached image of  the schematic.  They double checked that these values will work for a 12V – 24V adapter input. The PPD and APD have threshold voltages in order to enable them, however, it doesn’t appear that the given equations will meet these thresholds. Is this because the VSS and SGND are at different potentials?

 

Can you answer this question please?

 

Thanks for your help.

 

Regards,

 

WH

  • 0
    TI__Mastermind 40530 points
    Hi WH,

    Please clarify what your concern is. The adapter will be connected to either APD or PPD not both. Whichever one the customer chooses, it must go above that threshold stated in the datasheet.

    Also, please note that the 24V design you're referencing is not designed for a wide input range or 12V adapter input. This should really only be used with a 48V adapter if connected at the primary. Since the customer's current prospective 24V adapter is the same as the output voltage, I recommend doing ORing with a diode for example at the secondary.
  • 0 in reply to Darwin Fernandez
    Genius 4430 points

    Hi Darwin,

    I'll confirm if it is APD or PPD.

    The schematic TI provided (see below) indicates that it supports 24V & 48V external adapters, but you say it should only be used with 48V adapter.   Just wanted to confirm that the statement on the schematic " External Adapter 24V & 48V" is not correct. 

    Regards,

    WH

  • 0 in reply to WhiteHorse
    Genius 4430 points
    Looks like the customer will use the ORing diode option.
    Thanks for your help.
    WH