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LM61495: Use for aujust power supply application and need dynamic output from 5V to 30V

Sakura Lin
Prodigy 10 points
Part Number: LM61495

Tool/software:

Hello,

In our application, we need a MCU and DC-DC to make a adjust power supply unit with 36V input and 5-30V 10A dynamic output, and from https://www.ti.com/lit/an/slva861/slva861.pdf, we think we can use LM61495 for our design, however, we want to confirm about following questions.

  1. In the https://www.ti.com/lit/an/slva861/slva861.pdf, it suggest using a vdac connect with FB of DCDC, and about the caculate of Rset, for LM61495, the value of Rset should be what? and the vDAC need how many output ability? can stm32g431 dac working enough for it?
  2. For the dynamic adjusting, when the DAC output to FB, the output will change, and for example, when we want to change output voltage from 5V to 15V, we have to decrease the DAC voltage to let Vout increase. should I use a div to caculte the DAC (15V/1V, and change the DAC output 1/15*Vout, so that when Vout increase to 15V the Vfb is 1V) or just a value less than 1V and use something like PID to change it(change the DAC to 0.9V and when the Vout is near 15V ,change DAC back to 1V)? because accroding to the datasheet, the Vfb have a limit range, if we use the method 1 it seems will occur a fault of LM61495.
  3. Is there other DC-DC chips can use for our application? with 36V in and 5-30V out 10A. and can support dynamic adjust when working?

Thanks,

Siyu

  • 0
    TI__Genius 13045 points

    Hello Siyu,

    Please see my answers numbered to correspond to the questions:

    1) You would use the associated parameters in the EC table of the LM61495 datasheet along with your external feedback resistors to calculate the RSET value listed in application note. I can only provide comment on the buck converter.

    2) Use equation 3 in the application note to calculate the DAC value required for your desired output voltage

    3) This device is OK for 36Vin and 10A output.

    Best regards,

    Ridge

  • 0 in reply to Ridge Lahti
    Prodigy 10 points

    Hellp Ridge,

    For the design is the R3 a necessary one?, and can the DAC have enough V,I range to dirve the LM61495 for output range 5-30V? and also the when DAC output a high voltage, it seems will make LM61495 V RESET-OV/UV fault, so we have to change the DAC output at a small range right?

    Thanks,

    Siyu

  • 0 in reply to Sakura Lin
    TI__Genius 13045 points

    Hi Siyu,

    Yes, the feedback resistors are required. This is an adjustable output, meaning the top and bottom feedback resistors are required.

    I cannot provide comment on a specific DAC. It is up to you to select the appropriate device.

    The RESET flag is dependent on the FB voltage. Since you are using an adjustable output, the RESET output will depend on your set output voltage. Your FB voltage should always be 1V per the datasheet requirements. This scheme adjusts the FB network such that your output, based on the DAC input, reaches the appropriate FB value.  Please refer to Section 8.3.6 of the buck converter datasheet for details on the RESET flag.

    Best regards,

    Ridge

  • 0 in reply to Ridge Lahti
    Prodigy 10 points

    Hello Ridge,

    I test it with Pspice fo TI and it works well for my design, thanks for your help.

    Thanks,

    Siyu