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Hi,
I have PMP4447 based AC/DC converter that converts AC to 12 Vdc. And then, I am using TPS62125 as TI Webench suggested. Here is my schematics:
and the layout (TPS62125 is highlighted)
I have two issues with the TPS62125. I manufactured 100 pcs of this converter and I had almost 10-12% fail ratio. They were manufactured on a reflow oven by following standard reflow cycle (max 265 C for 5 sec). All failures were related to TPS62125 the modules worked fine after replacing the TPS62125. Somehow I also feel that it is too ESD sensitive.
The second issue is that those 80 of those 100 modules are on the field and I had failure on about 5 of them. Those 5 had a failure on TPS62125 and worked fine after replacing them with a new TPS62125. I am not sure if it was a spike, ESD, or anything else caused the problem, but it looks like TPS62125 is too gentle to use it. I wonder if there is any visible issue with my schematics or layout? I am considering to replace TPS62125 with TPS560200. Would you recommend TPS560200 as a replacement or another part?
The purpose of converting 3.2 V from 12V is to power CC26xx or CC13xx based RF chip. It is requires very low current. A consideration would be that it shouldn't cause disturbance to the RF chip.
Another question related to the above schematics. Would you recommend to use a TVS before the TPSxxx chip? I wonder if the 12V on PMP4447 may cause some spikes if there is any issue with the AC main. (it is an industrial application). I am using the same BOM list of the PMP 4447 including the Wurth Transformer.
I would appreciate your comments. Thank you.
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Hi Chris,
Thank you for your comments.
I am not really sure what is the issue. The main problem is that I have 12V output on the PSU but I don't observe any signal output at the output of TPS62125.
The below picture is from one module that was working when I test them at office, but failed on the field. It looks like I did a hand assembly
- As I experience from different cases, there should have been a physical damage on the case if there was an over voltage or current failure (none of the faulty modules have physical damage). CC2630 withdrawn very less current only about 7mA or less.
- I have observed the PCB by a thermal camera, there is no heat issue.
- I visually inspected all the modules if there is any short circuit, and then did continuity test by a DMM before powering the modules. There was no issue.
Do you guess any possible issue based on your experience what might be wrong? Would you suggest to place any protection circuit before TPS62125?
I am attaching the gerber files if it would be easier for you to see the layout (I can share eagle cad file as well).
Could it be layout related issue? One issue that maybe I should not have placed the inductor to the bottom layer to save space, instead keep them all on the same layer. What do you think?
Regarding the components I use:
C21, C22: 10uF, 25V, X6S, 10%, 0805: Part nr GRM21BC81E106KE11L
L21: 15uH, 750mA Par nmr: SRN4012T-150M
Regarding the ESD, the modules are produced in ESD-controlled environment, however, when we placed the modules into the enclosures, we didn't wear grounding straps and I noticed some of the modules broke after it. I assumed they broke because of the ESD issue (and due to very small package).
Thank you for the tip, I am not using the EN and PG pins. Then I can use like this, right?
If you would recommend me to replace TPS62125 with another one, what would you suggest considering that it is for an RF device? If it is possible, I would prefer something like SOT package instead of WSON that is less likely to cause soldering related problem.
Thank you very much