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TPS62300 – 3.3 V ouput has strange dips

Thomas Gundersen
Prodigy 20 points
Other Parts Discussed in Thread: TPS62300

Hi

We have a design where we use two TPS62300 to provide 1.1 V and 3.3 V. The schematic is shown in the first attachment. The problem is that the 3.3 V output has noticeable drops, se attachment #2. The problem appears when both regulators are loaded with a pure resistive load of 33 and 2.2 ohm for the 3.3 and 1.1 V respectively. The problem disappears if I disconnect the load from the 1.1 V output and the behavior is related to a limited range of loads, attachment #3 shows the behavior when the 1.1 V is disconnected. The behavior also disappears if the input voltage is increased to about 6 V.

We haven’t been able to find the source of this problem and would be thankful if somebody could help us.

 

 

 

  • 0
    TI__Guru*** 145940 points

    Is your testing being done on the EVM or your own board?  I recommend ordering the EVM and repeating the test.  Poor layout can cause issues to appear.

    If you are applying a signal to SYNC, I would recommend testing without that signal and seeing if that changes things.

  • 0 in reply to Chris Glaser
    Prodigy 20 points

    Hi again

    We have found the source of the problem. There’s an inductor in front of the regulators that we weren’t aware of and this inductor together with the capacitors caused oscillations in the 5 V input to the regulators. When we measured the voltage after the inductor we got the result shown in the picture below. The oscillations disappeared when we shorted the inductor.