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LMQ644A2-Q1: Schematic design review for 28V to 12V converter using LMQ644A2-Q1

Avishek Shaw
Prodigy 40 points
Part Number: LMQ644A2-Q1

Tool/software:

Hello everyone,

I'm working on designing a PCB using the LMQ644A2-Q1 step-down converter to get a 12V output at 12A from a 28V DC input. I based my design on the LMQ644A2 Quickstart Tool I previously used for a similar project.

Could anyone please review my schematic and advise if any modifications are necessary? I would appreciate any feedback or suggestions.

Additionally, I plan to operate the converter over a wider input voltage range of 12V to 36V while maintaining the same 12V output at 12A. Is it feasible to adjust the input voltage within this range without changing other components like resistors, capacitors, or inductors?

I've attached my schematic for reference.

LMQ644A2_Q1_28Vto12V.pdf

Thanks in advance for your help!

LMQ644A2_Q1_28Vto12V.pdf

  • 0
    TI__Mastermind 24115 points

    Hi,

    Can you please send over the quick start tool that you filled out for this schematic?

    Thank you,

    Joshua Austria

  • 0 in reply to Joshua Austria
    Prodigy 40 points

    Hi Sir,

    Please find the attached quick start tool.

    LM(Q)64480_A0_A2_Quickstart_Tool_REVA2.xlsm

  • 0 in reply to Avishek Shaw
    TI__Mastermind 24115 points

    Hi Avishek,

    Thank you for sharing that.

    I will take a look at this and get back to you by the end of the week.

    Best,

    Joshua Austria

  • +1 in reply to Joshua Austria
    TI__Mastermind 24115 points

    Hi,

    Based on the calculator, it does look like the schematic is valid. However I do have some concerns:

    • Please note that the inductor should be rated for at least as high as the high side switch current of this IC. This ensures that the inductor will not saturate in normal operation. For this device, that limit is 13.9A. 
    • The output capacitance seems to be fairly high. If you are seeing a slow transient response, I would recommend reducing this output capacitance to help speed up the loop response. Conversely, your load transient overshoot/undershoot may increase with less output capacitance, so those tradeoffs will need to be dependent on your application requirements.
    • It looks like the calculator has a concern on the junction temperature of the device as well when accounting for power losses. Please consider a lower switching frequency to help keep your junction temperature in safe range (less than 150C), unless you are using some other form of heat mitigation with this part (i.e. a heat sink, some alternative form of external cooling). Otherwise, this part will enter into thermal shutdown or continually operate in a temperature range that is out of spec of the device.

    Thank you,

    Joshua Austria

  • 0 in reply to Joshua Austria
    Prodigy 40 points

    Hi Sir,

    Thank you for your guidance and valuable suggestions. I will review the concerns you have highlighted and modify the design accordingly.

    Thanks and regards,
    Avishek Shaw