Hello, I am having a problem with a design using the ST8R00WPUR.
The input is 5v, the output is 10.5v, the load is 22 ohms (477mA).
The problem is that the output drops below 3v for 200ms when the load is applied, before returning to 10.5v.
The problem does not occur when the IC is warm. When the IC is at ~room temperature or below the problem occurs.
Here is the schematic:
C22 and C24 were originally 10uF as per the reference design, they were increased to 22uF to try and mitigate the problem (did not work). L2 has been tried with 4.7uH instead of 10uH, but the problem did not go away.
INH does not ever go below 2v
LX voltage looks very strange even when unloaded, there is a spike during the low cycle:
When the IC is warmed up, the spike goes away and the graph looks clean.
This issue does not occur on every PCBA we have with this design. We received 20 PCBAs from Supplier1 and none of them had this issue. We received 60 PCBAs from Supplier2 and about half of them had this issue.
Replacing the IC on 5 PCBAs fixed the issue on all of those PCBAs.
If the IC is swapped from a good board to a bad board and vice versa, the problem will follow the IC.
We had Supplier2 order new ICs from a different vendor and replace them, however the problem has remained.
Here are some scope shots showing the drop:
[Blue = INH]
[Blue = LX]
Here's how it looks on a 'good' board:
[Blue = INH]
I would appreciate any feedback/advice/speculation.
Thanks
