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TPS25831Q1EVM-062: Ccsp and Cbus

K.Yaita
Guru 29710 points
Part Number: TPS25831Q1EVM-062
Other Parts Discussed in Thread: TPS25831-Q1

Hi Team,

The schematic of TPS25831Q1EVM-062 shows Ccsp=22uF x 3 and Cbus=10uF.
On the other hand, the datasheet shows Ccsp=22uF x 5 and Cbus=1~4.7uF as the following.



Which is recommended value?

Best Regards,
Yaita

  • 0
    TI__Expert 8420 points

    Hi Yaita-san,

    The datasheet only show the recommend output cap value but the EVM is use the min cap value.

    If your customer switching frequency is 400Khz the min cap should be 44uF , if the switching frequency is 2Mhz the min output cap should be 33uF.

  • 0 in reply to Michael Tan
    Guru 29710 points

    Hi Michael-san,

    Thank you for your support.
    I understand the value in datasheet is recommended for Ccsp.

    Is 1~4.7uF recommended for Cbus?

    Best Regards,
    Yaita

  • 0 in reply to K.Yaita
    TI__Expert 8420 points

    Hi Yaita-san,

    The TPS25831-Q1 can be configured to external FET and without external FET current limit application.

    If you choose the external FET limit configuration, It still recommend choose 1~4.7uF cap for VBUS.

    If you don't choose the external FET limit but average current limit , you don't need to choose the 1~4.7uF cap for VBUS.

  • 0 in reply to Michael Tan
    Guru 29710 points

    Hi Michael-san,

    Thank you for your contiunous support.

    Table 12 shows Cbus=1~4.7uF irrespective of Buck Avg or Ext. NFET.
    Is Cbus=1~4.7uF recommended when my customer considers using Buck Avg?
    In addition, do you know why TPS25831Q1EVM-062 uses Cbus=10uF?

    Best Regards,
    Yaita

  • 0 in reply to K.Yaita
    TI__Expert 8420 points

    Hi Yaita-san,

    Yes, you customer can use 1~4.7uF for buck avg current limit configuration. There are not limitation for the Cbus cap value choosing.

    The EVM design is basic on type C 1.3 Specification , this old SPEC require the max Vbus cap value is 10uF, so it choose 10uF for the Cbus and need the external FET to block the CSP pin cap (5*22uF).  But now, the type C spec have update to 1.4 version , it change the Vbus cap max value to 3000uF. So more and more customer choose the buck avg for their application. It will save BOM cost.

    The point we need to consideration is the Ccsp value for buck loop stable consideration. That is why I suggest choose the min cap value  44uF for 400Khz and 33uF for 2Mhz.