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LM27313: Power Up Failing with No Load

Kevin LaRosa
Genius 17380 points
Part Number: LM27313

I am testing out using the LM27313 to boost from 5V to 7V and am seeing issues during startup.

Circuit:

Start-up:

I see that when I add a 100 mA load it seems to work:

Any suggestions?

  • 0
    TI__Guru* 76795 points
    Use a smaller inductance should help reduce the no load overshoot.
  • 0 in reply to Youhao Xi
    TI__Genius 17380 points

    Hi Youhao,

    Thank you for the suggestion. I tried reducing down to 2.2 uH and was still having problem.

    I took some additional scope shots of the SW node and saw that device appeared to keep switching even after overshooting. Next I checked the FB and it was above target, so I checked GND and saw that there was a significant spike on GND pin. I reviewed my layout and identified that the GND connection for this device was not well done and had an estimated 10 mohm of trace resistance due to no GND via nearby. I modified my EVM to have better GND and that seems to have fixed the issue. [Edit: I actually removed J15 during soldering and forgot to put it back, removal of the 30 uF load is what actually allowed it to stabilize].

    Thank you for your assistance.

  • 0 in reply to Kevin LaRosa
    TI__Genius 17380 points
    Hi Youhao,

    I tested today and realized changing the GND did not fix the issue, I had just removed the header on J15 connecting it to the 30 uF of capacitance it is supposed to power. With that connected it is unstable again. I'm unsure if the GND adjustment really made any difference. Any thoughts on whether I should continue reducing inductance below the minimum value I calculate based on the datasheet?
  • 0 in reply to Kevin LaRosa
    TI__Guru* 76795 points

    Hi Kevin,

    I am afraid the 30uF is too large for the internal loop compensation network to support. You may place a small resistor (0.1Ohm for instance) across J15 instead of shorting out J15, and see if the stability is regained.

    Thanks,

    Youhao