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TPS62147: Figure74

Shota Mago
Expert 7650 points
Part Number: TPS62147

Hi team,

My customer will use TPS62147 with Vin=12V, Vout=1.8V, fsw=1.25MHz. But Figure 74 shows switching frequency variation looks large around Vin=12V when Vout=1.8V.

  1. Why variation of fsw at below circled point is relatively large?
    (Is there any operation mode change at this point?)
  2. Is there any concern of deterioration of transient response at below point? 

Best regards,

Shota Mago

  • 0
    TI__Expert 7860 points

    Hello Shota,

    This variation is due to a change in operation mode. At the bottom of pg. 11 in the datasheet it mentions the case when VOUT/VIN < 0.15 that it does not enter Power Save Mode regardless of load current. This is why we see a slight shift in frequency at around 12V and shifts to a forced PWM mode instead of AEE.

    There shouldn't be any concern of significant transient response deterioration because the frequency change is minimal. 

    Thanks,

    Joseph

  • 0 in reply to Joseph Conrad
    TI__Expert 7650 points

    Hi Joseph,

    Thanks for your reply. Noted that the variation is caused by mode change. 

    If the device is operating in forced PWM mode(mode pin=high), there is not large switching frequency variation like Figure74. Is this understanding correct?

    Does all switching frequency vs input voltage graphs(Figure70~83) show at PFM/PWM mode(not forced PWM)?

    If yes, could you please provide same graph at forced PWM mode?

    Best regards,

    Shota Mago 

  • 0 in reply to Shota Mago
    TI__Expert 7860 points

    Hi Shota,

    I think there will still be some frequency variation vs. input voltage even in Forced PWM mode due to the nature of the DCS-Control. 

    I will double check with the team and get back to you soon.

    Thanks,

    Joseph

  • +1 in reply to Joseph Conrad
    TI__Expert 7860 points

    Shota,

    Confirmed that Figure 74 does show Forced PWM mode and its frequency variation vs. Vin. 

    This is actually due to the DCS-control minimum on-time and also propagation delays during FPWM mode (not AEE / PFM mode as I mentioned earlier) , which can cause frequency to drop slightly at larger input voltages.

    Regardless, transient performance shouldn't be affected for this application.

    Let me know if you have any other questions.

    Thanks,

    Joseph 

  • 0 in reply to Joseph Conrad
    TI__Expert 7650 points

    Hi Joseph,

    I understood. Thanks for confirmation.

    Best regards,

    Shota Mago