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LM51231-Q1: Voltage References and Phase Compensation

Yuya Shoji
Expert 3160 points
Part Number: LM51231-Q1

Hi team,

I have questions.

  • How can I decide the out put voltage?
  • How should I do for phase compensation?

Best Regards,

Shoji

  • 0
    TI__Genius 15755 points

    Hello Shoji,

    Thanks for reaching out to us via e2e.

    The output voltage is controlled via the TRK pin. Either use an external resistor divider or feed a voltage to that pin.
    Please also make sure that you will configure the correct output voltage range with the external resistance on the VREF/RANGE pin.
    See LM51231 datasheet Figure 7-6. TRK Control

    For the calcuation of the external components and the compensation network, please use the Quickstart Calculator which you can download from here:
    https://www.ti.com/tool/download/SLVRBJ1 

    Best regards,
    Harry

  • 0 in reply to Harry Hofner
    TI__Expert 3160 points

    Hi Harry,

    Thank you for providing the tool. This tool is for LM5123. Does this work for external component selection of LM51231-Q1?

    In my understandings of switching regulator, FB pin is compared with voltage reference, however, this chip has internal voltage divider(FB) and compare between the FB and reference generator. This makes me confused. Could you tell me here structure background? This is one of my concern for output voltage regulation and phase compensation.

    Best Regards,

    Shoji

  • +1 in reply to Yuya Shoji
    TI__Genius 15755 points

    Hello Shoji,

    Yes, the tool also works for the LM51231.

    The LM5123(1) is using an internal feedback divider because it is more precise and also consumes less power.
    But you cannot change the rsistor values.
    Therefore, instead of comparing the FB signal to a fixed internal reference, it is just vice versa here.
    The FB signal is compared to a flexible reference which is controlled via the TRK pin.

    See pin description for TRK and VREF/RANGE pins on page 4
    and section 7.3.7 Adjustable Output Regulation Target (VOUT, TRK, VREF Pin) on page 18 of the datasheet

    Best regards,
    Harry