• State Resolved
  • Locked Locked
  • Replies 3 replies
  • Subscribers 63 subscribers
  • Views 471 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

driving capacitive load with LMR12010

Janez Humar
Prodigy 70 points
Other Parts Discussed in Thread: LMR12010

Hello,

In my application I need large storage capacitor (2 x 4700uF) on output side of a regulator (LMR12010), for driving GSM module. On primary side I have also even larger storage with higher voltage (12V) as a reservoir for sending warning message in case if aux. power supply is lost. 

I works fine but I noticed unwanted voltage ripple on output voltage (3.6V). This ripple (300mVp-p) has quite low frequnecy from 8 to 50Hz depending on load.

I tried adding " feed forward capacitor with a value between 470pf and 1000pf across the top feedback resistor (R1)" as recommended in a datasheet, I tried to add additional low ESR ceramic 10uF capacitor right on output but non of it helps. Not even ripple voltage frequency has changed.

Any idea what should I do to reduce this quite big ripple voltage?

Thanks in advance

Janez Humar

  • 0
    TI__Genius 15810 points

    Hello,

    With ~10mF at the output, the control loop is very heavily damped and without any phase boost network the response might be unstable. Adding a Cff in the order of pFs is not going to be helpful at all. The low frequency oscillation might in fact be the control loop complaining. Do you know your capacitor's ESR? As an experiment you could try adding a 100mohm resistor in series withe cap to ground. This will increase your equivalent ESR. While you will see a larger switching ripple, it might help stabilize the loop and reduce the low frequency oscillation. Let me know if that helps.

    Regards,
    Akshay

  • 0 in reply to Akshay Mehta
    Prodigy 70 points

    Hi Akshay,

    Thanks for feedback. I thought that such big capacitors have bad enough ESR so I will not have this problems.

    It turned out that ESR is much better.

    Adding resistor as you explanied is not good for me, because I need the complete voltage on capacitors and voltage drop on that resistor during heavy current surges when GSM is sending would be to big.

    What I did is adding such resistor also in series with cap but not to ground. I inserted it between output of regulator and cap. And it works fine :-)

    Thanks againg for a hint.

    Regards

    Janez

  • 0 in reply to Janez Humar
    TI__Genius 15810 points

    I'm glad it helped. 

    Regards,

    Akshay