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TL720M05-Q1: LDO is oscillating with recommended low ESR-MLCC

Marks Greulich
Intellectual 540 points
Part Number: TL720M05-Q1

Hi guys,

I`m a bit confused about the behavour of the above mentioned LDO. I have an 22uF MLCC and several other MLCC`s at the ICs which are supplied by that LDO (5V). e.g. 100nF/1uF/4,7uF.

Regarding to the datasheet of the LDO he could work with a C > 22uF and low ESRs.

The funny story now is that I see an oscillation at the 5V output around +/-200mV and if I use a wired electrolyth cap at the output the oscillation is totally gone. So the high ESR of that electrolyth cap seems to help. But I couldnt use it under that rough environment.

I have it on all of my TL720M5-Q1 LDOs on my PCB, also if only a 22uF and a 10uF is at the 5V output. But there the oscillation effect is a bit less.

What could I do here or has someone an explenation for that effect?

BR,
Markus

  • 0
    TI__Intellectual 835 points

    Hi Marks,

      Stability is one of the tricky things in LDO. low ESR is not always the best. it depends on the design.

      The  figure below was from page7 of the datasheet. From this table, for 22uF load capacitance, the required ESR should be approx 0.5 ohm or more for stability. Maybe your MLCC caps have lesser ESR than this? could you share the part number of your caps so we can find out their ESR?   I'll use caps with  5ohms > ESR > 1ohm to be safe. 

    Regards,

    Chito

  • 0 in reply to Chito Tapia
    Intellectual 540 points

    Hi Chito,

    ah I havent seen that graph in the datasheet. Only the reeding a Minimum ESR of 1mR what is quite less ofcourse.

    So I soldered a 1 ohm in series to my 22uF at the Output and...totally gone and stable.

    Hopefully I dont open any other Problem list with that resistor :-)

    Thanks,

    Markus

  • 0 in reply to Marks Greulich
    TI__Intellectual 835 points

    Hi Markus,

     Glad to hear that the issue is solved. Let us know if you find other problems.

    Regards,

    Chito