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TPS63900: Excessive output ringing using NB-IoT modul

Part Number: TPS63900

Hello,

my test setup is a follow:

*) TPS63900EVM evaluation board
    The switches are configured for an output of 3.3V and unlimited current
    The input has an additional 470uF capacitor
*) Input is a 3.3V benchtop power supply (also tried 2 AA cell batteries)
*) Output is connected to a Quectel BC95-G NB-IoT modul
    The modul is configured to automatically dial-in to the network on power up
*) Picture of the test setup
    

Sometime after power on (I think when the modul tries to dial-in and uses more current), the output voltage looks like this:
    

I've already tried adding various capacitors at the input and/or output but nothing really changed.
I know the oscilloscope probe connection is not ideal, but shortening the GND wire to just a few mm doesn't make any difference here.

Any ideas what could be wrong ?
Maybe just a measurement error ?
I can't believe this device doesn't work as expected as it's exactly made for powering i.e. NB-IoT modules ...

Thanks and best regards,
Berni

  • Right after posting this question I've already found the solution myself.
    The antenna of the NB-IoT module is to close to the test setup and therefore induces great disturbances.
    After moving the antenna about 2 meters away everything works fine ...