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TPS65261-1: Lx Absolute max

Yusuke Mukuno
Expert 7395 points
Part Number: TPS65261-1

Hi Expert,

My customer found the issue about Lx pin negative voltage ringing. (minimum around -2V)

Zoom-in

Absolute max of Lx pin : -1V to 20V

This waveform is reached negative side(-2V)

Is it any problem?

Also, Datasheet is described "LX1, LX2, LX3 (Maximum withstand voltage transient < 20 ns) ".

What is meaning  "LX1, LX2, LX3 (Maximum withstand voltage transient < 20 ns) "?

Also, Coud you please let me know the min/max value, if  transient < 20 ns?

Thanks

Muk

  • 0
    TI__Genius 13451 points

    Hi Muk!

    Following are comments:

    (1) Maximum withstand voltage transient < 20 ns means when adding a 20V voltage in LX pin and GND exceeds 20ns, the device may be damaged. It is not suggested to add a 20V voltage less but close 20ns. It is suggest to design following the recommend value.

    (2) About the negative voltage problem, please provide the Layout and marked the test position for further analysis.

    Shuai

  • 0
    TI__Mastermind 23620 points

    Hi Muk,

    Thanks for reaching out. 

    1.IDo you measure the LX waveform with minimum loop method(Simply remove the hat from the probe tip and wrap a wire around the probe barrel for the ground connection.)?

    2.When LX node voltage dropping below -1V every switching cycle, it does not mean that it will damage the device. This voltage is caused by the output inductor driving current through a MOSFET body diode during switching operation. Most buck converters appear to violate this limit during switching operation, dropping below –1 V briefly every switching cycle. As Shuai clarified, maximum withstand voltage transient < 20 ns means when adding a 20V voltage in LX pin and GND exceeds 20ns, the device may be damaged.

    3. For more detailed explanation and layout guidance, please find this document.   

    Understanding the Absolute Maximum Ratings of the SW Node

    You can also send layout for me to review. lucia-gao@ti.com

    Let me know if there is any more concern. Thanks!

    BRs

    Lucia