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TPS61087: Output voltage of TPS61087

Y.Ottey
Mastermind 6145 points
Part Number: TPS61087

Dear all,

I would like to ask about TPS61087.

When the output voltage is set from 9V to 8V (setting the values of R1 and R2 to match the output voltage of 8V) using the same circuit as the data sheet Figure.16 (the following circuit), the output voltage only increases to 5V.
(At this time, 330Ω is connected to the load.)

The output voltage remains at 5V even if the following measures (measures to increase the ON time) are taken.
・Lower input voltage than 3.3V
・Try a load of 330Ω or more.
・Replaced the inductor at 4.7, 10, 18, 27uH.

If there are any conceivable factors, please let me know.
When I check the datasheet, it seems that Rcomp and Ccomp need to be set to 8V, but I would like to know if there are other possible factors.

Best Regards,

Y.Ottey

  • 0
    TI__Mastermind 40080 points

    Dear Sir,

    I think there has some soldering issue on the board, please remove the feedback resistor and solder it again.

    By the way, what is R1 and R2 value you soldered on the board?

  • 0 in reply to Helen chen
    Mastermind 6145 points

    Dear Helen

    Thank you for your reply.

    "I think there has some soldering issue on the board, please remove the feedback resistor and solder it again."

    Does the "feedback resistor" shown above refer to R1 and R2 on the circuit?
    Also, could you tell me why you think that the output voltage only goes up to 5V due to "some soldering issue on the board"?

    "By the way, what is R1 and R2 value you soldered on the board?"

    The above is currently being confirmed.
    Is the above question to check if R1 and R2 are set as calculated below?

     

     

    Regards,

    Y.Ottey

  • 0 in reply to Y.Ottey
    TI__Guru 58225 points

    Dear Y. Ottey,

    Please check if the output voltage changes when you start with no load on the output.

    Would you please share the resistor values you are using for R1 and R2?

  • 0 in reply to Y.Ottey
    TI__Mastermind 40080 points

    Thanks Brigitte :)

    Hi Ottey,

    Yes, R1 and R2 should be the value calculated by the below equation:  if Vo=8V, R2=17.8k,  then R1=97.6k .   By the way, what kind of board did you use? Is it TPS61087 EVM board?

  • 0 in reply to Helen chen
    Mastermind 6145 points

    Dear Helen and Brigitte

    Thank you for your reply.

    There are additional things to check.
    When the circuit is confirmed, it is a circuit in which the operational amplifier is connected to the wiring of the FB terminal as shown in the figure below.
    The reason is that I want to change the output of TPS61087 by injecting the voltage from the operational amplifier.

    In this case, will the IC be damaged if voltage is injected from the output of the operational amplifier while the TPS61087 is not started?
    (Detailed circuits can be sent to you in a private message.)

    Regards,

    Y.Ottey

  • 0 in reply to Y.Ottey
    TI__Mastermind 40080 points

    Hi Ottey,

    Will not be damaged. But I'm wondering this kind of connection may leads to error.

    It should decoupling the output of amp and the FB. a RC filter is needed before connecting to the FB.  And the amp should be connected as a voltage follower.

  • 0 in reply to Helen chen
    Mastermind 6145 points

    Dear Helen

    Thank you for your reply.

    "It should decoupling the output of amp and the FB. a RC filter is needed before connecting to the FB.  And the amp should be connected as a voltage follower."

    When I checked the circuit, it was as follows

    ・ There is no RC filter between the FB terminal and the output of the amplifier.
    ・ The part with the amplifier is a non-inverting amplifier circuit (calculated the amplification factor is 5.1V / V)
    What kind of error is possible in this case?
    (If all goes well, I'll send you a detailed circuit in a private message.)

    Regards,

    Y.Ottey

     

  • 0 in reply to Y.Ottey
    Mastermind 6145 points

    Dear Helen

    I have an additional question for you.
    "And the amp should be connected as a voltage follower."

    Please explain the reason why the peripheral circuit of the amplifier is used as a voltage follower as described above.

    In addition to my previous post, I would be happy if you could answer.

    Regards,

    Y.Ottey

  • 0 in reply to Y.Ottey
    TI__Mastermind 40080 points

    Hi Ottey,

    The part with the amplifier is a non-inverting amplifier circuit (calculated the amplification factor is 5.1V / V)? could you please send the related circuit to me?

  • 0 in reply to Y.Ottey
    TI__Mastermind 40080 points

    To decoupling the circuit, or its hard to get the target voltage.  But anyway, I need the exact circuit for a study.

  • 0 in reply to Helen chen
    Mastermind 6145 points

    Dear Helen

    Thank you for your reply.

    I will send you a detailed circuit with a private message.

    Regards,

    Y.Ottey

  • 0 in reply to Y.Ottey
    TI__Mastermind 40080 points

    OK！ Please close this post.