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TPS61088: Schematic review

Allen Lu
Intellectual 2440 points
Part Number: TPS61088

hi team:

 my customer uses the TPS61088 device for car system ,it is required to test the Loop Compensation Test. would you kindly support  this SCH review cases ?

  • 0
    TI__Expert 5180 points

    Hi Allen,

    Could you please share Vin range, Vout and load current for further review? If want to calculate Loop Compensation more accurately, pls also share part numbers of Cout or package, rated voltage of Cout. thanks.

    Best Regards,

    Eric Yue

  • 0 in reply to Eric Yue
    TI__Intellectual 2440 points

    Hi Eric:

     kindly check this additional info for your reference.

    Vbat(2.5~4.2)Vin->5V/2A,  2*47UF Ceramic capacitors as 1210package,  10V rated voltage.

    System 5Vin->8.2Vout/2A,  2*22UF Ceramic capacitors as 1210package,   25V rated voltage.

  • 0 in reply to Allen Lu
    TI__Expert 5180 points

    Hi Allen,

    Thanks for your update.

    Vbat sch: If the chip is always EN by input supply, the EN pin can be pulled up to VCC pin because VCC is more stable than Vin. The current comp will lead to very high bandwidth and poor phase margin. It is recommended to change Rcomp to ~20k and Ccomp to ~4.7nF. I cannot see ILIMT resistor clearly because it covered by silk value, please set this resistor based on input peak current value. 

    System sch: Also The current comp will lead to very high bandwidth and poor phase margin. It is recommended to change Rcomp to ~20k and Ccomp to ~4.7nF. I notice the ILIMT resistor is 51k, if so, this value may beyond the recommended range. Customer can change it to 100k.

    Best Regards,

    Eric Yue 

  • 0 in reply to Eric Yue
    TI__Intellectual 2440 points

    hello Eric:

     would you share the excel formulas to me?  it is a little difference between your recommendation and Webench design.  And i also attach the excel file ,kindly check this ~

     and what s the recommend value of the C808 and C902?

    TPS61088 loop calculation.xlsx

  • 0 in reply to Allen Lu
    TI__Expert 5180 points

    Hi Allen,

    Customer can refer to this excel to calculate and the little difference will not effect the control loop very much. I think the little difference is because of effective output cap which is used 114uF in excel, in real application this value should be smaller according of DC bias.

    Best Regards,

    Eric Yue

  • 0 in reply to Allen Lu
    TI__Expert 5180 points

    C808 and C902 effect is not as important as Ccomp and Rcomp. Customer can use small value ~dozens of pF first and adjust them in real bench test. Typically we just leave this space in case of need, you may find in many EVM design this cap is NC as well.

  • 0 in reply to Eric Yue
    TI__Intellectual 2440 points

    Hi Eric:

     Recently i check the loop test, after change the Rcomp and Ccomp as you mentioned. i want to sync up with you some confusion that the Vbat sch is still work abnormal, do you have any suggestion? tks in advance. 

    System 5Vin->8.2Vout/2A:(without changing Rcomp to ~20k and Ccomp to ~4.7nF)

    Vbat(2.5~4.2)Vin->5V/2A(changing the Rcomp to ~20k and Ccomp to ~4.7nF)

  • 0 in reply to Allen Lu
    TI__Expert 5180 points

    Hi Allen,

    Both two bode plots look strange, could you please check whether the wire connection or measurement is correct? The bod plot should be similar to the calculated one in the excel tool. Or maybe you can use another DCDC EVM to check the connection first. 

    Best Regards,

    Eric Yue