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Part Number: BUF18830
Now the customer is using BUF18830.
Below is the SCH.
When the picture displayed on the panel is changing, a ringing is observed as below.
Below is the waveform on OUTx pin. (The ringing amplitude is a little different from each other)
Below is the power rail of VS (powered by AVDD of TPS65177)
Could you please give some suggestion about that?
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In reply to Diaara:
In reply to Robin Yu:
I am sorry but for some reasons my last answer was not published.
What is the value of AVDD and the part# of the output caps? I think that this increased output capacitance should not be necessary and the resulting transient on AVDD is poorer that I would expect. Please see the attached scope plots showing the load transient measurement results on AVDD of TPS65177 and OUTx of BUF18830; I used these devices EVMs for the test and connected AVDD to Vs.
Could you please measure again with a scope during the transient event AVDD on C260 and C675? I want to make sure that we optimize first this transient response because OUTx should follow then.
Do you have any update regarding this issue?
Great thanks for your attention for this case.
The customer reflects that adding cap close to Vs pin doesn't help a lot.
Now it is still on a holiday of China, no more feedback from them.
I would go to field to have a look.
Do you have some more suggestions to figure out the problem?
Below is the waveform at C260 and C675 node.
Waveforms of BUF18830.docx
There is some difference between them. After current sensing circuit, some ripple is observed on AVDD rail.
And also, for OUT1 and OUT2, the waveforms are really different.
I have tried to add capacitors on several Vs pins (double to 10uF*2), but no obvious improvement is observed.
And customers themselves have also tried to add capacitors on OUTx pins, a little improvement is observed.
Any suggestion for this case.
Thanks for posting the waveforms.
On the initial schematic you posted I see that on the COMP pin there is an additional capacitor to ground C285 in parallel to C288-R110. Is this one mounted? If yes I would recommend to remove it and redo the transient measurement without it because it is much too big and this could be the reason of the bad transient behavior of AVDD converter.
I think you refer to C289, actually I had taken it off. Before it was taken off, the transient time was almost 2ms, while now it is about tens of micro seconds.
All the waveforms I send to you are tested in the condition C289 is taken off.
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