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TPS23754EVM-383: The component of ACF circuit selection

Part Number: TPS23754EVM-383

Hi

Below is the secondary circuit of our design. Vout is 15V.

Please see ZD1 & ZD2 . We select Vz=12V zener diode.

Is there any risk or wrong of the electrical characteristics of ZD1 & ZD2?

Does Vz value relate to the voltage of Vout?

Thanks.

Wendy

  • Hey Wendy, 

    The diode helps bias the base of the NPN transistors. The higher the voltage, the higher the current through the transistor. Higher current means the FET is going to turn off faster. A higher output voltage means the gate voltage is also higher, unless you adjusted the resistor dividers. So it just depends on the other design choices. It is probably fine, but you can test the normal operation and check out the gate/drain waveforms to ensure the FET is not exceeding VDS max. 

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

     

    Regards, 

     

    Michael P.

    Applications Engineer

    Texas Instruments 

  • Hi Michael

    1. If I choose Vz=15V ,is it better than the current design?

        Because I found that TI choose Vz=12V for TPS23754EVM-383 circuit ,and the Vout=12V 

        Is the Vz value depend on the output level?

    2. Could you help to check is the value of L7(22uH) suitable for 15V/2A output?

        Would it make ripple more than 15%?  

    Thanks

    Wendy

  • Hello Wendy, 

    1. We have  not done a 15V ACF so i don't know based on lab results. Our 24V ACF's use 10V zener clamps, so I think 12V is probably fine for a 15V output. Choice is yours. 

    2. Use the Power Stage Designer Tool to estimate the current ripple of the inductor. 

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

     

    Regards, 

     

    Michael P.

    Applications Engineer

    Texas Instruments