Hello,
I've built two devices, one of them realizes wireless charging receiver with BQ51050B and works good with any Qi mobile chargers. However I'm facing a problems with second device which is transmitter using BQ500212. Transmitter is powered from 5V (USB) and Qi compatibility is not necessary. I will appreciate if you could check my project.
First of all, receiver part is built according to SLUUA25C doc (http://www.ti.com/lit/ug/sluua25c/sluua25c.pdf) and uses this coil (WE 760308103205): http://www.digikey.com/product-detail/en/760308103205/732-6210-ND/5050820 And as I wrote - works fine.
For transmitter I choose 2.5W design (as I need something between low power and 5W). So I followed exactly this scheme: http://www.ti.com/lit/ug/tidu586/tidu586.pdf Coil from BOM was taken: http://www.digikey.com/product-detail/en/760308101103/732-5673-ND/4947874 . And it doesn't work. I risked and used 2 layer pcb but took care of grounds separation, and put as much ground plane on the bottom layer as it was possible. Copper thickness is 35um.
I suppose I have problems with communication between Tx and Rx. I observe that LED connected to Vrect is flashing and Vrect is increasing but Tx suddenly stops power transfer. According to troubleshoot doc I left opened FOD, PMOD, FOD_CAL and LOSS_THR as well and shorted LED_MODE to ground. For NTC I just use a resistor and have about 3V on T_SENSE.
Here I attache scheme (kicad .sch and png), more scopes and gerber of pcb: dl.dropboxusercontent.com/.../bq500212a_debug.rar
Below I attache images of a pcb and some scopes. Yellow scope is always for Tx (coil comm side or comm+ pin) and Blue scope is always waveform of Rx coil.
Part of pcb:
Scopes:
Yellow - TX Coil (coil comm side). Blue - RX Coil
the same scope connection as above
Yellow - comm side coil. Blue Rx Coil
COMM+ Pin of BQ500212 without RX coil under TX coil.
More scopes are attached in .rar file.
If you could give me any hints I would be very gratefull. Maybe I should try to take larger coil for TX?
Best Regards!