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TPS63070: About Output capacitor calucuration

teritama
Expert 2185 points
Part Number: TPS63070

Tool/software:

Hi team,

In datasheet p18, in the caseof RHPZ<400kHz, it is said that more output capacitor should be added to reduce the cross over frequency. Are there any method of calucuration the recommended value of output capacitor about RHPZ?

We find recommended value on datasheet p4(this is the case of L=1.5uH) and Typical capacitors on Table 6. However, our customer would like to have a deshign method to use as guide in adjusting the output capacitor value.

If you have any data of output capacitor vs RHPZ, it is quite helpful.

Best regards,

teritama

  • +1
    TI__Mastermind 32350 points

    Hi  Teritama,

    First, RHPZ has no relationship with Cout as you can see in the equation 9. RHPZ is decided by Vout, Iout, Vin and inductance.

    Change the Cout just can adjust the pole caused by Rload and Cout, then you can adjust the cross frequenct not too close with RHPZ. Mostly, fcross should be 1/5 or less than RHPZ. If they are close, open-loop may have double cross and the PM is not enough during the second cross.

    We do not have calculation tool for this device, so i am sorry that i can not give you a quick way to anlysis, but i think you can just follow the typical application schematic. That should be fine.

    Regards

    Tao

  • 0 in reply to Tao Zhang
    Expert 2185 points

    Hi Tao-san,

    Thank you for reply and sorry for responce delay. I undersand the suggestion about Cout in datasheet is not for RHPZ but also fcross adjust. 

    In this device, how we calcurate fcross? I understand it seems to be enough follow the typical application from your answer. However we want to provide the information to the customer how to caluculate fcross roughly.

    Best regards,

    teritama

  • 0 in reply to teritama
    TI__Mastermind 32350 points

    Hi  Teritama,

    Yes, i got  your point, but the problem is that we do not have calculation tools for this device yet.

    Regards

    Tao

  • 0 in reply to Tao Zhang
    Expert 2185 points

    Hi Tao-san,


    I see. I would suggest the customer to set output capasitor follow typical application example initially. And if they found unstable when load transient analysys, suggest to use larger capasitor value at output capacitor below 470uF followed in datasheet.

    Best regards,

    teritama

  • 0 in reply to teritama
    TI__Mastermind 32350 points

    Hi  Teritama,

    Thanks for your understanding.

    Let me know if you have further questions. 

    Regards

    Tao