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TPS62110 SwitcherPro problem

JatanNaik
Expert 4011 points
Other Parts Discussed in Thread: TPS62110, TPS62111

We recently used SwitcherPro to model the TPS62110.  We entered the following design specifications (Vin: 6.1-6.5V, Vout=1.8V @ 300mA), and SwitcherPro generated a default design with a 33uH inductor and 22uF output capacitor.  However, the program indicated that this design's phase margin was too low (less than 30 deg).  This seems to contradict the datasheet, which states that as long as the L x C product is greater than 6.2uH x 22uF, the converter will have enough phase margin.  Also, the 33uH inductor recommended by the program is bigger than the largest value the datasheet recommends (22uH).  Only by lowering the inductor to 10uH was I able to obtain a phase margin of above 40 degrees in SwitcherPro.  Also, I should mention that the SwitcherPro efficiency graph shows that the efficiency is less than 70% across the output current range.  This is significantly lower than the efficiency listed in the datasheet. Can you please correct the simulation?  Thanks for your help!

  • 0
    TI__Intellectual 1280 points

    jatan,

    try sending the design to me.  I'd like to see what inductor and cap you used.  It's possible that the default component selection isn't ideal in terms of efficiency.

    heath@ti.com

  • 0 in reply to Heath Gallimore
    TI__Expert 4011 points

    Heath,

    It's the default design that the program generates using the following specifications: Vin: 6.1-6.5V, Vout=1.8V, Iout: 300mA

    Regards,

    Jatan

  • 0 in reply to JatanNaik
    Prodigy 50 points

    I have more or less the same problem with the SwitcherPro online version 3.1.22 and the TPS62110. If I choose an input voltage from 7 to 12V and an output voltage of 3.3V with an output current of 1A, there comes a message under the schematic:

     

    “The gain of the compensation is exceeding the gain of the open loop error amplifier! This is unrealistic because the open loop error amplifier bounds the compensation. Without correct compensation the design will most likely be unstable. To fix the problem, lower the target crossover frequency or change the compensation to fit inside the bounds of the Error Amplifier. ”

     

    If I change the component values in order to reach the values from the Datasheet or evaluation module, the message stays the same.

     

    After that, I tried to work with the TPS62111, which have no compensation network outside, but the error message still stay.

     

    Where is the bug?

  • 0 in reply to Aseol
    TI__Intellectual 2710 points

    Yes, this is an issue with TPS6211x designs in SwitcherPro. We are working on fixing it and it will be released in our next version v3.2 on July 31st.

     Thanks,

    Hetal Joshi

    Senior Developer and Project Manager

    Analog eLab Design Center

    HPA Design Tools

    Texas Instruments, Inc.

     

    TI makes no warranties and assumes no liability for applications assistance or customer product design. You are fully responsible for all design decisions and engineering with regard to your products, including decisions relating to application of TI products. By providing technical information, TI does not intend to offer or provide engineering services or advice concerning your designs.

     

  • 0 in reply to Aseol
    TI__Intellectual 1280 points

    Our new version v3.2 will show up on the web on Friday July 31st.  This bug is fixed along with many others. 

    Basically with this part you can't change the compensation, because it's internal.  So no matter what design happens you'd get this warning.  We had a single open loop error amp  gain showing up that intersected the correct compensated error ampliver gain.  This is of course unrealistic as typically the error amp open loop gain bounds the compensated version of it.  But this part doesn't really work this way it has several other confidential things that happen inside that basically make this warning not applicable for this family of devices.  But the SwitcherPro tool doesn't understand that so we've basically removed the open loop gain bound in order to remove the warning. 

    TI makes no warranties and assumes no liability for applications assistance or customer product design. You are fully responsible for all design decisions and engineering with regard to your products, including decisions relating to application of TI products. By providing technical information, TI does not intend to offer or provide engineering services or advice concerning your designs.

  • 0 in reply to Heath Gallimore
    Prodigy 50 points

    Ok,

    Thanks for your answer, that makes the whole context more clear.