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TPS63802: Feed Forward Capacitor Experiment

Lim Phang Moh
Intellectual 270 points

Part Number: TPS63802

Hi guys,

After measuring the quiescent current of the TPS63802 across an input voltage range of 3-5V, I notice the quiescent current can vary from 11 uA to 27 uA across that 3-5V input range.

So, I started to add the feed forward capacitor with several values like 10 pF, 47 pF, 100 pF and even a ridiculous 100 nF.

I notice that the quiescent current is a lot more stable across the entire range of the input 3-5V like 16-20 uA with the additional feed forward capacitor.

However, it won't be able to reach the minimum 11 uA anymore and I also notice that with the additional feed forward capacitor, the current transient spike of few hundred uA take place like the following input voltage range:

  • 3-3.3V: transient current spike is below 40 uA.
  • 3.4-3.8V: transient current spike is around 400-500 uA
  • 3.9-5.0V: transient current spike is below 40 uA.

Without the feed forward capacitor, the transient current spike is in the few hundred uA range (500-800 uA) for the entire 3-5 V input voltage.

I have used 47 uF (GRM188R60J476ME15D) at both the input and output of the TPS63802. With a smaller 22 uF capacitor for the input and output, the current consumption is even less stable and have a bigger range for a specific input voltage.

Of course, my aim was to have 11 uA quiescent current for the entire input voltage range or around there as I see from the datasheet it shouldn't be jumping more than 1-2 uA from 11 uA across 3-5 V input voltage.

What are your thoughts on this guys?

  • 0
    TI__Mastermind 32350 points

    Hi Lim，

    Nice to see you again.

    During our test for quiescent current, we use device only. so, that is right, you will always get a higher consumption with external componets.

    With a feed-forward cap, the peak current and switching time will change, i think that's the root cause.

    you can find some difference with or without feed-forward cap.

    without feed-forward cap

    with feed-forward cap

    Regards

    Tao

  • 0 in reply to Tao Zhang
    Intellectual 270 points

    Hi Tao,

    For sure during quiescent current test, I only mounted the TPS63082 circuitry and nothing else. Of course I can achieve 11 uA at 3.6 V (I think this is the VIN your datasheet to refer to when the quiescent current is measured).

    May I know what value of feed forward capacitor in pF you use in your case?

    My aim is the circuit is able to deliver up to 2A (transient) for 3-5 V input.

  • 0 in reply to Lim Phang Moh
    TI__Mastermind 32350 points

    Hi   Lim.

    it is 10pF in my test.

    Regards

    Tao