TPS55330: Upstream TPS55330 boost followed by downstream TPS62130 buck is unstable

Hi KarlKracht,

Can you share the schematic? Have you probed the TPS55330 startup waveform, like Vin, Vout, SW, iL?

I can share the schematic, but who else can see it in this forum? It's proprietary.

k

schematic and oscilloscope screenshot attached in a .zip file.

in the scope shot, yellow trace is 7V input driven by benchtop supply. In schematic, signal name is 7V0_IN.

in the scope shot, blue trace is 15V output of U8. in schematic, signal name is 15V0.

in the scope shot, pink trace is 3.9V output of U7. in schematic, signal name is 3V9.

I can't tell if the file I attached is actually attached. I may have attached it twice. please let me know if you receive it.

kfor_TI_2020_06_25.zipfor_TI_2020_06_25.zip

Hello Karl,

Yes, you attached the file and it is attached twice, but we will take it and review it. Please give us some days to answer.

Hi Karl,

1. From the share scope shot, the yellow trace input is not stable and has more than 2V spikes. Please firstly make sure the benchtop supply has enough current capability. Have you checked the supply current limit level? You can add a bulk aluminum electrolytic capacitor at input to make input voltage stable first.

2. Have you checked the TPS55330 and TPS62130 circuit loop stability separately? You can add a 1A load at TPS55340 output and runs a load transient to see if the phase margin is enough. Then implement the same test for TPS62130.

3. Are the failures easily to replicate and happening on all boards? Did the layout follow TI's datasheet layout guidelines?

Hi Karl,

Is there any update?