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ADP1032 startup problem

Category: Hardware
Product Number: ADP1032ACPZ-2-R7


I've been having a problem when performing a power up on a ADP1032ACPZ-2-R7.

When applying EN the output power VOUT1 start up nicely. FB1 looks OK. PWRGD also goes to high as expected. Then, after ca. 25 ms both FB1 and VOUT1 start oscillating. This goes on for about 2.4 seconds and then stops again and all signals are fine. During oscillation a buzzing sound is audible. Does anyone have a clue what could cause this behaviour? 

I attached part of the schematic and the output waveform where

[1] yellow: PWRGD

[2] red: EN

[3] blue: FB1

[4] green: VOUT1



  • Hi Marc,

    Thank you for your question.

    I believe that the ADP1032 is hitting current limit.

    May I know the loading condition for the ADP1032; how much current in the VOUT1 and VOUT2 your load is drawing?

    in the datasheet, we have some typical plots that shows the maximum output current you can get for a specific VIN and VOUT conditions. See Figure 22 and Figure 39.



  • Hi Jefferson

    Thank you for the quick answer. Current consumption is not a problem.

    Could there be another source for this behaviour?

    Strangely, we have three other prototypes which don't show this startup behaviour. This one board worries me though. We had an issue that the first layout led the FB1 signal line to close to the inductance of the boost converter (L2003_1) which prevented the flyback converter to work properly.

    Best Regards


  • Hi Marc,

    Yes, the FB1 signal line close to noisy nodes like the inductor/transformer can cause the part to behave abnormally as the FB1 signal line is picking up a lot of noise. It is recommended in the layout that the FB1 signal line and the feedback resistors were placed away from the noisy area like the Switch nodes/inductors/transformers.

    Can you share the snapshot of the layout for this board for review.

    Thanks and regards,