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TPS549B22: About switching frequency

tsuyoshi tokumoto
Expert 2630 points
Part Number: TPS549B22

Hello Team,

  My customer evaluated a switching frequency of TPS549B22 on his prototype board.
  The evaluation results were approximately 70kHz to 130kHz lower than the values listed on the datasheet.
   *Please see the attached file.

Measurement result.xlsx

  Could you please tell me the reason?

  If you need any additional information, please let me know.

Sincerely,
Tsuyoshi Tokumoto

  • 0
    TI__Intellectual 2460 points
    Hello Tokumoto-san,
    Can you please tell me more details of the measurement technique on frequency? Did your customer measure the frequency on the scope or through average value? if they were on the scope, can you please share the waveform?
    Kit
  • 0 in reply to Kit Nguyen
    Expert 2630 points

    Hello Kit-san,

    　Thank you very much for your prompt reply.
    　I shared the waveforms with you.
    　　*Please see the attached file.

    Measurement result2.xlsx
    Thank you and best regards,
    Tsuyoshi Tokumoto

  • 0 in reply to tsuyoshi tokumoto
    TI__Intellectual 1520 points

    Hello Tsuyoshi-san,

    The TPS549B22 switching frequency does vary with VIN, VOUT, and IOUT. This is the nature of our constant on-time controller.  In the datasheet, we only specify the frequency range at VIN=12V and VOUT=1V. So with the VOUT=4.16V, you will see this frequency variation.  This is just the capability of our basic Ton generator.

    Thank you.

    Amnat

  • 0 in reply to Newey Yakamna
    Expert 2630 points

    Hello Amnat-san,

    　Thank you very much for your prompt reply.
    　I understand your explanation.
    　I thought that the impact by Vout(4.2V) was small,
    　because TPS549B22 has adaptive On-Time Control function.

    　Please let me ask you an additional question.
    　Under the following conditions,I am thinking about estimating
    　the switching frequency value at approximately 100 kHz lower value
    　than the data sheet value.

    　Vin:12V
    　Vout:4.2V
    　　1)MFR_SPECIFIC_03[7:0]＝0xB2
    　　　- Data sheet value
    　　　　　min:490kHz typ:550kHz max:615kHz
    　　　- Evaluation result
    　　　　　452kHz
    　　　- Estimation value
    　　　　　min:390kHz typ:450kHz max:515kHz

    　　2)MFR_SPECIFIC_03[7:0]＝0xB3
    　　　- Data sheet value
    　　　　　min:585kHz typ:650kHz max:740kHz
    　　　- Evaluation result
    　　　　　546kHz
    　　　- Estimation value
    　　　　　min:485kHz typ:550kHz max:640kHz

    　Is my thinking reasonable?

    Thank you and best regards,
    Tsuyoshi Tokumoto

  • 0 in reply to tsuyoshi tokumoto
    TI__Intellectual 1520 points
    Hi Tsuyoshi-san,

    Yes, your thinking is reasonable. From looking back at some captured data for the 12VIN and 5VOUT at 650kHz setting, I was seeing the measured frequency at ~575kHz. Even though this is not the 4.2VOUT, the measured value is still within your approximate 100kHz lower value tolerance range.
    Thank you.
    Amnat
  • 0 in reply to Newey Yakamna
    Expert 2630 points

    Hello Amnat-san,

    　I appreciate your prompt reply and your additional information.
    　I will tell the results of our discussion to my customer today.

    Thank you and best regards,
    Tsuyoshi Tokumoto