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Original question:

TPS23758EVM-080: Changing output voltage on TPS23758EVM

TPS23758EVM-080: TPS23758EVM-080: Changing output voltage on TPS23758EVM

Tim Hsu
Prodigy 70 points
Part Number: TPS23758EVM-080
Other Parts Discussed in Thread: TPS23758

Hi, we also have some similar issue of evaluating output voltage.

I need to make it slightly higher than 5V, maybe 5.2-5.5V.

Is there any guides or tool kits for us to reference, thank you.

Tim 

  • 0
    TI__Mastermind 21320 points

    Hello Tim,

    Please use the following equations to determine the new resistor divider values (for R19 and R24)

    If this post answers your question, please indicate so by marking this thread as resolved. Thank you.

     

    Regards, 

     

    Michael P.

    Applications Engineer

    Texas Instruments 

  • 0 in reply to Michael Pahl
    Prodigy 70 points

    Hi , according to EVM R1=200K R2=36.5K we measured  Vout=5.1V Vpp=70mV.(Vin source is POE)

    As I changed the FB resistance to R1=200K R2=33K we measured Vout=5.7V Vpp=250mV(Vin source is POE)

    How do we overcome the Vpp problem in this case? Can we tune the COMP capacitance and resistance to achieve it?

    Thank You

  • 0 in reply to Tim Hsu
    TI__Mastermind 21320 points

    Hello Tim,

    I am glad to hear you were able to successfully change the output voltage. 

    To decrease the output ripple, one thing you can do is increase the output capacitance. The following equation is a guideline. Alternatively you can guess and check in the lab :) 

    Another suggestion is to use electrolytic caps as well.  

    If this post answers your question, please indicate so by marking this thread as resolved. Thank you.

     

    Regards, 

     

    Michael P.

    Applications Engineer

    Texas Instruments 

  • 0 in reply to Michael Pahl
    Prodigy 70 points

    Hi Micheal, we already increased Cout to 860UF , but it didn't improve much.

    So I am wondering, how to progress the FB accuracy in this kind of architecture.(TPS23758 is a primary side regulation system)

    Thank you,

    Tim

  • 0 in reply to Tim Hsu
    TI__Mastermind 21320 points

    Hello Tim,

    When you mention accuracy, are you talking about ripple or load regulation?

    You could also try changing the snubber values across the FET Q1 to lower the peak voltage. 

    Did you use eletrolytic or ceramic caps? Also, what voltage value did the caps have?

    Try using 330uF electrolytic and a 0.1uF ceramic on the output. 

    If this post answers your question, please indicate so by marking this thread as resolved. Thank you.

     

    Regards, 

     

    Michael P.

    Applications Engineer

    Texas Instruments