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LM51581: Can LM51581 output voltage be changed by an external controller using Figure 4 circuit in TI application report " SLVAEJ4"?

Part Number: LM51581
Other Parts Discussed in Thread: TINA-TI

Hello guys,

One of my customers is considering using LM51581 for their new products.
They want to design a variable output voltage power supply (PS) using LM51581.
Their target PS spec is the follow.
Vin=5V, Vout=6V~40V, Io=50mA, variable output voltage step=10 steps between 6V~40V.
They found the following TI application note which describes about variable output voltage.

Application Report
SLVAEJ4–December 2019
Design of the Adjustable VOUT Boost Circuit
https://www.ti.com/lit/an/slvaej4/slvaej4.pdf

They have the following questions at the moment.
Q1,Can Figure 4 in the application note be applied to LM51581?
Q2. If Q1 answer is yes, is there any concerning point to design the PS?

Your reply would be much appreciated.

Best regards,
Kazuya.

  • Hi Kazuya,

    thank you for using the E2E forum.

    Yes, this is possible with the LM51581 as well.

    The power stage needs to be dimension correct for the different output voltages (worst case).

    And check the compensation for all the possible operation modes.

    Best regards,

     Stefan

  • Hi Stefan,

    Thank you very much for your reply.

    Could you please tell me what "dimension correct" meaning is?
    Also how can I check the compensation(phase margin). Is Webench or TINA-TI recommended to check it? 

    Thank you again and best regards,
    Kazuya.

  • Hi Kazuya,

    dimension means the selection of the components according the Voltage, Current requirements - so you need to check for all the different output voltage settings as the tools normally only give the information for a fixed output.

    This esp. applies to Quickstart tool and Webench.

    Compenstation can be checked with

    - Quickstart calc

    - Webench

    - PowerStage Designer

    - Measrument on the application board (always recommended as this give the real behavior).

    Best regards,

     Stefan

  • Hi Stefan,

    Thank you very much for your reply.
    I understood!

    Thank you again and best regards,
    Kazuya.