• State Resolved
  • Locked Locked
  • Replies 5 replies
  • Answers 1 answer
  • Subscribers 63 subscribers
  • Views 256 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

LM51772: DTRK

Shuji Ishiwata
Mastermind 8880 points

Part Number: LM51772

Hi All,

I have a question about the DTRK pin of the LM51772.

The VOUT voltage is set using an I2C register.
In this case, is it possible to dynamically adjust the output voltage by inputting a PWM signal to the DTRK pin?

I also understand that the Vout feedback method is selected as follows when the IC starts up (RST is released).
If the FB pin is connected to VCC2 at startup (internal FB), Vout is set via I2C.
At startup, the FB pin is voltage-divided by an external resistor (external FB), and the voltage is set by external resistor voltage division.
I understand that the feedback method cannot be switched while the IC is operating. Is this correct?


Best Regards,
Ishiwata

  • 0
    TI__Guru 69091 points

    Hi Ishiwata,

    the selection of internal of external FB is done during startup (nRST going high). After the it is fixed till  the next low - high cycle of nRST. It cannot be set or modified via I2C.

    If the FB pin is above the defined threshold (e.g. with connection to VCC2) at startup, internal FB is selected and Vout is set via I2C.

    In this mode (internal FB) you can still use ATRK and DTRK to adjust the output voltage.

    It will then scale down the output voltage like described for the external FB.

    Best regards,

     Stefan

  • 0 in reply to Stefan Schauer
    Mastermind 8880 points

    Hi Stefan,

    Thank you for your answer.

    Let me clarify and confirm if my understanding is correct.

    (1) I understand that when using the internal FB, it is possible to dynamically adjust the output voltage by inputting a PWM signal to the DTRK pin. Is my understanding correct?

    (2) It is not possible to switch between the internal and external FB while the device is operating. This is because nRST is fixed until the next low-high cycle. Is my understanding correct?

    Best Regards,
    Ishiwata

  • +1 in reply to Shuji Ishiwata
    TI__Guru 69091 points

    Hi Ishiwata,

    yes, your understanding is correct for both points.

    Best regards,

     Stefan

  • 0 in reply to Stefan Schauer
    Mastermind 8880 points

    Hi Stefan,


    I have some additional questions.

    (1) If the output voltage is varied using the DTRK pin, will the DVS slew rate setting set in the DVS_SLEW_RAMP register take effect?

    (2) If the DVS_SLEW_RAMP register setting is not reflected, how can I set the slew rate when varying the output voltage?


    Best Regards,
    Ishiwata

  • +1 in reply to Shuji Ishiwata
    TI__Guru 69091 points

    Hi Ishiwata,

    DVS is only applied to output voltage changes done via the I2C VOUT register.

    For ATRK and DTRK you have it under your control on how fast you change the output voltage target on ATRK or DTRK.

    So in this case the slow rate follows the change in PWM Duty cycle for DTRK or analog voltage change on ATRK.

    Best regards,

     Stefan