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LM51571-Q1: Stability issue at -40C and 105C

sibichakkaravarthy Dhayalan
Prodigy 30 points
Part Number: LM51571-Q1
Other Parts Discussed in Thread: LM5157

Am using LM5157 Boost regulator for my application, I have used following compensator ranges 

My regulator will fail at -40C ranges, I have screen shot of test result for reference

Kindly do needful.

Thanks,

Sibichakkaravarthy D

  • 0
    TI__Genius 11215 points

    Hello, 

    Thanks for reaching out. Can you please share the specs of you design (Vin, Vout, Iout) and the complete schematics? What type of capacitors do you have at the output of your board (e.g. ceramic, aluminum etc)? Usually when instability is seen only at very cold temperature, it means that the ESR of the output capacitor is much higher than its nominal value (even 20x) and this is inserting an additional zero in the Bode plot which might cause instability. We're looking forward to hearing from you.

    Kind regards,
    EM 

  • 0 in reply to EM
    Prodigy 30 points

    Vin=8 Vout=18 Iout=1A

    We are using two aluminum electrolytic capacitor with low esr along with one ceramic capacitor - 68uf_35V

    its Part no: 35CE68AXT

  • 0 in reply to sibichakkaravarthy Dhayalan
    TI__Genius 11215 points

    Hello, 

    Thanks for sharing this info. It seems like there is also a ferrite at the output, did you try to first measure your circuit without the ferrite? As there is a capacitor in parallel to the bottom feedback resistor, did you see a lot of noise on the feedback? Would you mind please checking the design with the Excel calculator ( https://www.ti.com/lit/zip/snvr511v ) and make sure the compensation fits for higher ESR values and at the minimum Vin and full load? 

    Kind regards,
    EM