TPS56C230: After Boot, the output will continue to climb and cannot be stabilized

Hi, you may Change to eco mode or increase inductor to 0.68uH to check if helps.

Yuchang

Hi Yuchcng

Afterwards, I tried to confirm the correctness of each peripheral component. The Rlower resistance used 8.x K-ohm during production. After I adjusted it back to 10K, it can work normally.

But anyway, I am still worried that there is something wrong with my design, because even with the wrong voltage divider resistance, the output should be a fixed value, why does it appear that it cannot be fixed at a specific voltage?

BR, Delun

Hi Delun,

Yuchang will check your question and reply you soon.

Hi Delun, when used 8.xK, the upper resistor also has been changed to keep Vout with 0.8V, right?

And did you compare the Switching waveform before and after lower resistor change? 

I will review layout tomorrow and Iworried wether negative OC protection was triggered due to smaller inductor in FCCM mode, that’s why I asked you to change to Eco mode or increasing inductor to try. 

Yuchang

HI Yuchang

Because in the Bring up stage, I only to check the voltage level first, this is not the setting I expected, so the upper resistor is still kept at 3.32K, I just accidentally discovered that the EMS factory used the wrong Rlower, and I found this unstable phenomenon.

I have tried to change to ECO mode and change the choke. In the case of 8.xK, the voltage will continue to increase, but I don't think this will be the situation triggered by OC, because the output voltage is increased, and the power will not be cut off.

Or, is there a minimum Rlower limit for 56c230? (longitude dependent of internal comparator?)

BR ,Delun

Delun, I remembered there was no 10K low limitation for lower resistor, and I will try on board tomorrow.

What I meant is triggering NOC, negative OC, if IC working at FCCM mode with smaller inductor, negative OC may be triggered, which will cause high-side FET turns on unexpected, that's may cause Vout goes higher than normal.

And I checked layout, seems switching node from PMIC is close to feedback net, not sure if some noise coupled. Did try to disable the PMIC to try?

Another is please try to change upper resistor to keep Vout with 0.8V when using 8.xK lower resistor and check if issue still gone...

HI Yuchang,

I tried to adjust the upper resistor to 2.74k, but it didn't improve.
In addition, I can't disconnect the PMIC temporarily, so I jump the FB off the PCB (also includes the upper/lower resistors), and the same is not improved.

BR,

Delun

Hi Delun, I still would you try disable the PMIC or make this channel not work, like removing the inductor or entering protection...

And also you may try to change lower resistor different value under 10K to try if all values trigger the issue, such as 5k, 3k..

One more question, what's end voltage after soft-start end? will it be stable?

I will try to double check on EVM tomorrow with smaller resistor for lower Rfb.

Yuchang

Hi Yuchang

The same happens when I remove the inductor.
After the Soft-start completes, the vboot voltage is correct, but it will continue to slowly drift up until about 1.2V and then stop.

Br, Delun

Delun,

It's weird that currently seems only increasing the lower resistor could make the issue gone, right?

And I would find a EVM to try same configuration but sorry there is no EVM available in hand now.

I re-checked the schematic, could you please check if remove PC40 and check if the issue still happen with 8.xK resistor?  

And as I mentioned if you have comparison waveform between normal and abnormal startup(complete process), please share for review, catch Vout/SS/SW/VIN, zoom in and zoom out.

Finally I would check if there is possible to make 56c230 work lonely, disable all others hardware, just would confirm this is caused by 56C230 circuit itself.

Yuchang