TPS23754: Are these two IC branded 2ATG4 A64P counterfeit?

Hi Ray,

Thanks for reaching out!

Could you share the schematic of your PD + DC/DC circuit? I would like to see if there are any application related concerns, and maybe minor chip feature changes can make a pass/fail.

Also, when hiccup happened, were you running a test with a standard PSE or a injector/bench power supply?

Best regards,

Diang

Hi Diang,

Our China CM has made nearly 30 of these pcba with this power supply and this is the first instance of 10 pcba built we had 6/10 pcba with this "hiccup" error, and all 10 pcba had glitchy behavior to some extent. Some boards you can hear the "hiccup" audibly. I tried two days off and on to fix this by following data sheet and your advice for an earlier issue and finally changed the IC and the issue went away.

Based on the branding of the two ICs I replaced compared to the top IC in the image I see a difference.

 These are not "minor" pass fail corner case, these devices all had issues to one extent or another and replacing the ICs with Digikey parts corrected the "hiccuping" completely and the drive waveforms of the device were corrected.

PS: Our CM spot buy these suspect IC from http://www.ickey.cn for your information.

Waveform of FET at xfmr primary with suspect IC.

Waveform of FET at xfmr primary with Suspect IC replaced with Digikey, no other changes to pcba components.

We got the same results on TP Link POE+ switch or PhiHong #: POE60U-1BTE-R IEEE802.3BT - POE 60W injector.

I could not attach a file so this is all I can give you for a schematic.

Hi Ray,

Thanks for your information. I saw two things could be related:

1. Start up delay is not enough and output cap is too large: You may use a 100k R and a smaller 47uF output cap

2. The input cap is too high. Stannard needs 80 - 120nF input caps. It is recommend only keep the 100nF near VDD-Vss and changes other caps to 1nF instead.

Best regards,

Diang

Hi Diang,

We have your notes recommending these changes from the last time we had an issue. 

RE: TPS23754: Using xfmr Coilcraft POE40Q-24ED with TPS23754-hiccups on POE++ 56V

The root cause of the prior issue /\ above /\ was the APD pin was floating so the PS was trying to switch to Aux mode upon boot.This was corrected with no further issues.

As I said earlier, we have built approximately 30 of these pcba with no issue at all using the schematic shown.

\/ Below new issue we are now experiencing \/

For the defective IC issue, we tried all of those modifications, remember I told you I worked on this for two days, tried everything you have recommended in the past and those modifications changed nothing.

With the defective IC installed what we found was that on some boards removing both 22uf caps then the IC would not reboot the POE Supply, but would still "hiccup" constantly with that odd waveform xfmr primary. Before we removed the two 22uf caps the POE+ supply would constantly hiccup and reboot.

But with new IC (no other change to the PCBA components-virgin boards) the board operates quite well and we can load it to the maximum VA capability (Since wave 20 W RMS 1 kHz into 8 ohms) with no problem at all and it will operate its on board DSP, Ethernet, 24V, 5V, 3.3V and ARM processor no issues.

Previously we have ran this design on older PCBA build for weeks on a resistive load. I will consider your modifications going forward as I agree with most of them, but they did not correct the hiccup-only changing the TPS23754 IC fixed the boards-modified per your advice and not modified.

Tomorrow I will replace the rest of the pcba with Digikey IC and report what happens.

PS: I am starting to suspect that perhaps the IC was not well soldered to the VIA heatsink surface below the IC. I saw what looked like solder adhesion beneath the suspect ICs I changed.

Tomorrow I will reflow a couple of defective boards with suspect IC and see what happens.  During this testing our camera saw no hotspots on the board so not sure about this theory.

Thanks for your advice!

Hi Ray,

Thanks for your additional information. 

Personally I would have some concerns especially the 24V Vout with 220uF cap will cause too much inrush energy. But if you had tried multiple ways to check, and A-B-A swap method shows the issue follows with PD chip, you could replace all chips and consider submitting a failure analysis to check if the chips are not good. 

Best regards,

Diang 

Hi Ray,

Glad to hear you found the root cause and the issue was solved! I will close this thread for now. Please reply or open a new thread if you have further questions or concerns.

Best regards,

Diang