STWBC86 TX powers on and off every 4 seconds

[JFDuvalEng]

Hi all, I designed a custom 5W charger around the STWBC86. I programmed the config and patch found in STSW-WBC86FWBPP to the IC using WPSTUDIO and I got it to charge my device (another custom circuit, this one using a TI BQ51050 receiver IC)... for 4 seconds. Every four seconds or so it turns off, then starts again.

I can tell it turns off by monitoring the input current (550mA when active, brief period around 400mA, then less than 10mA). The PWR_TRANSFER_ON LED matches what I see on my power supply. This input current is consistent with off-the-shelf chargers used with my RX circuit.

My RX circuit works with off-the-shelf Qi chargers. If I try to charge something else (my phone, or my headphones) I get a tiny red blip (maybe 0.5s) instead of 4s. I suspect those peripherals are trying to pull way more than 500mA.

The documentation on this chip is extremely limited, and I have yet to find what is causing this problem. The IC temperature is OK, and the GUI isn't showing me any errors. Could you please assist me with this? It would be really helpful if I could get a reference manual that explains what the registers do, and what some of the acronyms in the GUI mean. Thanks!

[JFDuvalEng · Accepted solution]

I'm replying here just in case someone else faces the same problem. While my schematic shows a bidirectional TVS on the ring node, I accidentally picked a unidirectional part number. The way my board was assembled prevented that node from going above 650mV. After removing the diode the charger stayed on.

[JAKE2]

Hello, I have something similar experience, and the problem just disappears somehow.

(I am not the ST employee, best way is to contact with ST's FAE)

But I have some suggestion that may help you.

① I suggest try go to BQ51050's GUI (no idea what tool they offer), and switch to BPP (not EPP)

 → Maybe it may occur any delays because negotiation phase includes something detail information exchanges compare to BPP.

② Is it properly designed regarding matching capacitors between coil , and the coil's inductance, both your TX and RX IC

③ Try cut the VBUS wire with the knife and connect the load between GND with it. If there are no load, it may blink.

Or try to contact the manufacturer where you bought the STWBC86 IC.

[willzhou]

For software support you can access 

https://github.com/STwirelesscharger/