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LM2576HV: 24V Webench Design

Jejomar Ildefonso
Genius 9500 points
Part Number: LM2576HV
Other Parts Discussed in Thread: LM2576

Hi Team,

Our customer is currently working with LM2576HV and he used this design generated from Webench: https://webench.ti.com/appinfo/webench/scripts/SDP.cgi?ID=5678F641D6A8FF3D 

Customer's query is as follows:

"Attached are my schematic and layout. The LM2576HV chip heats up and sometimes fails. I selected a value from the data table. Now I saw that I had chosen a large value of Rfbb (R11=2kΩ), but I can try changing it to 1k. The Schottky diode is 1A, while in the Webench project, it is 5A. Do you really need a diode with such a large current?

Also, from the table, I selected an inductance of 470 μH, while in the Webench project, the inductance is 2.2 mH. Which of these parameters may have caused the issue?"

Thanks in advance!


Kind Regards,

Jejomar

LM2576_SCH.pdf

LM2576_PCB.pdf

  • 0
    TI__Mastermind 35210 points

    Hello Jejomar,

    Can I get some additional information

    Jejomar Ildefonso said:
    e LM2576HV chip heats up and sometimes fails

    By fail do you mean the device destructively shuts down or the device goes into thermal shutdown (resolved with power cycle will long off time)?

    Jejomar Ildefonso said:
    . Do you really need a diode with such a large current?

    The diode and inductor should be able to support the peak current sustain within these devices. That would be the peak current limit (5.8A typ). The saturation current of the inductor for example should be appropriately rated for that.

  • 0 in reply to Marshall_Beck
    TI__Genius 9500 points

    Hi Marshall,

    Thank you for looking into this.

    Marshall_Beck said:
    By fail do you mean the device destructively shuts down or the device goes into thermal shutdown (resolved with power cycle will long off time)?

    Chip fails - Vout = Vin. Between terminals 1 and 2 (LM2576) the resistance is 154 ohms. Attached is a photo of the destroyed chip.





    I designed the circuit according to the datasheet. Now my schematic looks like this:

    SCH_new.pdf

    The inductance of 150μH is indicated in the datasheet. I originally had 470 µH (0,6 A). Now I put 100 µH (1A). And in the Webench design, the inductance is 15 times greater (2.2 mH).

    So I bought such a board below where the inductance is 47 μH. It works normally and does not heat up at a current of 0.2 A to 1.5A.




    But I would like to ask why is my chip heating up? Now it has a temperature of 52-54°C.



    Please let me know if you need further information regarding our set-up.


    Kind Regards,

    Jejomar




  • +1 in reply to Jejomar Ildefonso
    TI__Mastermind 35210 points

    Hello Jejomar,

    I have seen this board design before. It has came off ebay. The failure mode looks like EOS. I would confirm that they ordered from an authorized distributor. I am pretty confident they did not and the part being genuine may not be true.