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LM25141-Q1: low temp condition, when power on the output is abnormal.

Colt Zhang
Expert 3370 points
Part Number: LM25141-Q1
Other Parts Discussed in Thread: LM25141

Tool/software:

hi expert,

my customer use LM25141-Q1 power for SOC PMIC. now when in -20℃ or -40℃， the output is abnormal, below is the test scope(channel 3 is the output):

of course i also let customer test the LM25141-Q1 in the normal temp condition:

PWM MODE

SW: 

OUTPUT ripple voltage :

 

i think this may be is the loop problem, could you help review their design and give the solution how to deal this problem.

schematic:1346.LM25141.pdf

calculation tool input LM25141-Q1 Quickstart Tool （BUK9Y2R8-40H）- revA2.xlsm:

  • 0
    TI__Guru 64325 points

    Hello

    We will review and get back to you as soon as possible.

    Thanks

  • 0
    TI__Genius 13995 points

    Hello,

    I am actively reviewing this issue and plan to reply by mid next week with recommendations.

    Best regards,

    Ridge 

  • 0 in reply to Ridge Lahti
    TI__Expert 3370 points

    hi Ridge,

    this problem is very urgent, could you help accelerate the progress in next Monday.

  • 0 in reply to Colt Zhang
    TI__Genius 13995 points

    Hi Colt,

    I have the following comments for the customer schematic,

    • For 18A, and Fsw=440kHz the 3.3uH inductor is very large. You want to target 30% current ripple for a peak current mode buck converter. I do see that 18A is listed on the schematic for only 100us. What is the expected nominal load current?

    • The phase margin of the existing design is too low. The customer should be targeting 60 degrees, and the calculator estimates less than 40 for their design at room temperature. Since there is little existing margin for stability, it is recommended that the customer reduce their desired crossover frequency to 10% of the switching frequency and follow the calculator recommendations for compensation. Here is what I calculate for 59 degrees of phase margin:
      • Rc1=1.15k, Cc1=33nF, Cc2=560pF
      • Please note that they must recalculate if their inductor or output capacitance changes.

    • Can the customer provide part numbers for their output capacitors? At cold temperature, it could be that the output capacitance is de-rating to the point that the buck converter loop is no longer stable.

    Best regards,

    Ridge