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LM5145: RE : Submission for Design Review

JAYAKRISHNAKUMAR S
Prodigy 160 points
Part Number: LM5145
Other Parts Discussed in Thread: CSD18563Q5A, LM61480

Design Requirements:

Input Voltage Range: 9V - 36V

Output Voltage: 5V 

Output Current: 8A

Max Allowable Voltage Ripple(peak to peak): 100mV

Find the attachment below that contains the design file for the above requirement submitted for the TI review and share the comment for the same

sch_501-1-02018_lm5145.zip

 

  • 0
    TI__Mastermind 49207 points

    Hello, please complete and send the LM5145 quickstart calculator for this design: https://www.ti.com/tool/LM5145DESIGN-CALC. The schematic looks okay, but you can use 60V FETs if Vinmax is 36V. Try CSD18563Q5A. Also, you can tie the NC pins to GND.

    Note we have the LM61480 36V, 8A converter if you want a smaller, easier to implement solution without external FETs (which are difficult to source at the moment).

    Regards,

    Tim

  • 0 in reply to Timothy Hegarty
    Prodigy 160 points

    Hi Tim,

    We had done some modifications to the design and we had attached the latest design file and also we had completed the Quickstart calculator. please find the latest file

    lm5145 ti review.zip

  • 0 in reply to JAYAKRISHNAKUMAR S
    TI__Mastermind 49207 points

    The same comments as before apply related to the FETs (use 40V or 60V devices). Here are some additional comments:

    1. Use one RT resistor as this is a noise-sensitive node.
    2. Current limit seems very high at 20A. 12A (150% of full load) is more suitable.
    3. Use the derated value for Cout with voltage in the quickstart. Is 66uF correct at 5VDC? Cold is typically lowest effective capacitance.
    4. Target crossover frequency should be 10% of Fsw (40-50kHz). Update the compensation values accordingly.

    Regards,

    Tim

  • 0 in reply to Timothy Hegarty
    Prodigy 160 points

    Hi Tim, Please find the Response to your valuable comment below

    1.)The same comments as before apply related to the FETs (use 40V or 60V devices). -- as we are having more stock we are using the same FET. May I know the Impact of using the FET?
    2.)Use one RT resistor as this is a noise-sensitive node. -- changed based on your suggestion.
    3.)Current limit seems very high at 20A. 12A (150% of full load) is more suitable. -- changed based on your suggestion
    4.)Use the derated value for Cout with voltage in the quickstart. Is 66uF correct at 5VDC? Cold is typically the lowest effective capacitance. -- Ok we are looking into this.
    5.)Target crossover frequency should be 10% of FSW (40-50kHz).
    Update the compensation values accordingly. -- changed based on your suggestion.

    Please find the updated Design file and the Quickstart calculator below and let me know your feedback/comment on this.

    LM5145 TI REVIEW B1.zip

  • 0 in reply to JAYAKRISHNAKUMAR S
    TI__Mastermind 49207 points

    Thanks for the updated file. I will take a look at it tomorrow as today is a holiday in the US.

    Regards,

    Tim

  • 0 in reply to JAYAKRISHNAKUMAR S
    TI__Mastermind 49207 points

    The quickstart calculator looks good - just target the crossover frequency a bit higher (10-15% of Fsw is good -- 40-60kHz in this case) and update the compensation values accordingly. Also, check that 66uF is actually the effective value for ceramic output cap at 5VDC.

    In terms of the schematic, tie the NC pins of the controller to GND for better GND plane area. Also, consider using a slightly lower Rdson low-side MOSFET. No need for 80V FETs if Vin -max is 36V -- try CSD18563Q5A 60V FETs instead.

    Regards,

    Tim