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LM26480-Q1: Switching pin's absolute maximum voltage

YY
Intellectual 2100 points
Part Number: LM26480-Q1
Other Parts Discussed in Thread: LM26420-Q1,

Hello Team,

My customer asks me what is the absolute max for SW pins.

I found absolute voltage value at input pins.

However, I don't find the value for SW pins in the datasheet.

even though, LM26420-Q1 has SW pin's absolute max voltage value in the datasheet.

Could you please send me the value?

Best Regards,

Yuki

  • 0
    TI__Mastermind 30260 points

    YY,

    SW1 and SW2 do not have absolute maximum values because they are not input pins.

    However, if they were added to this section they would be listed with the same values as all other pins: -0.3V to +6V

  • 0 in reply to Brian Berner
    TI__Intellectual 2100 points

    Hello Brian,

    thank you for your support.

    My customer found the large overshoot and undershoot at switching waveform.

    therefore, they have been concerned that LM26480-Q1 may be broken by overshoot and undershoot.

    the undershoot peak voltage was -1.4V at 3ns.

    and overshoot peak voltage was 7.3V at 3ns.

    LM26480-Q1 is keeping its operation.

    Can I say no problem for using LM25480-Q1 with large over/undershoot to my customer?

    Best Regards,

    Yuki

  • 0 in reply to YY
    TI__Mastermind 30260 points

    Please provide oscilloscope screen capture showing overshoot and undershoot on switching node (SW1, SW2).

    Also, it would help if you attach schematic of your design.

    If you follow recommendations in datasheet for external components, especially for output inductor and output capacitors, it should ensure your design is within acceptable limits.

    All switching regulators have overshoot and undershoot at the switching node during switching (high-side FET turn ON/OFF and low-side FET turn ON/OFF), and in most cases it is acceptable. However, I cannot be sure without examining your design and measurements  taken in the lab.

  • 0 in reply to Brian Berner
    TI__Intellectual 2100 points

    LM26480_SW waveform.xlsxHello Brian-san,

    I got waveform.

    Could you please check it and send me your comment?

    Best Regards,

    Yuki

  • 0 in reply to YY
    TI__Mastermind 30260 points

    The overshoot and undershoot on the SWx net that you measured looks normal to me.

    Since you did not attach schematic, you need to confirm the following:

    • the output inductormeets the requirements in the LM26480-Q1 datasheet:
      • LSW1,2 = 2.2 µH, DCR <= 70 mΩ
    • The feedback networkmatches Table 5. Buck External Component Selection
      • R1 and R2, C1 and C2 correct for target VOUT
    • the input/output capacitors meets the requirements
      • CIN  (Capacitance for stability) 10uF minimum
      • COUT  (Capacitance for stability) 10uF minimum
      • CIN, COUT: Low-ESR Surface-Mount Ceramic Capacitors (MLCCs) used in setting electrical characteristics.

    If the schematic follows recommendations, the component should be able to withstand overshoot and undershoot at the switching node that is inherent to every switching regulator.

  • 0 in reply to Brian Berner
    TI__Intellectual 2100 points

    Hello Brian-san,

    I can't attach the schematic to public website dur to I have NDA with customer.

    But, I can confirm that external parts are matching with your suggestion.

    Inductor was Sunlord's SWPA4018S2R2 which has 2.2uH value and DCR max is 59m ohm.

    Cin and Cout capacitances are ceramic caps and have enough capacitance value 2x 22uF each.

    feedback components are also match with datasheet recommendation.

    So, the overshoot and undershoot has no problem for LM26480-Q1.

    Is my understand correct?

    Best Regards,

    Yuki

  • 0 in reply to YY
    TI__Mastermind 30260 points

    Yuki,

    The final responsibility for ensuring the PMIC is working correctly in the application is owned by the customer. The system must be tested thoroughly across all operating conditions, including corner cases, to ensure the PMIC is still functional after stress testing for VIN min/max, Ambient Temp min/max, output Load min/max, variances in passive components, and all other environmental variables not listed here.

    From my perspective, the overshoot/undershoot on the switching node that you provided (SW1 or SW2) looks normal and I do not expect any issues because the PMIC itself is creating the condition which exceeds min/max. This is understood by designers and the absolute minimum and maximum specifications generally apply only to device inputs.

    However, my opinion (regardless of my expertise in this area) is not legally binding and cannot be used as a method to say that "TI endorsed this application and ensured that it is acceptable" if there is an attempt to return or seek compensation for failed parts. The TI Legal Disclaimer is added at the end of every datasheet, which explains the TI's legal policy. The customer's responsibility is explained in this section:

    These resources are intended for skilled developers designing with TI products. You are solely responsible for (1) selecting the appropriate TI products for your application, (2) designing, validating and testing your application, and (3) ensuring your application meets applicable standards, and any other safety, security, or other requirements.