ST,
My team and I have designed a Qi wireless Transmitter (TX) based closely off the STEVAL-ISB044V1, sharing the STWBC-EP controller and the overall block diagram. The principle difference is more robust front end protection, (Fuse, zener, RPP, TVS) which is unrelated to the problem we're seeing, we believe.
The legacy product it's replacing is an off the shelf, basically just a flash mem, 4-channel op-amp, a P and a N-channel FET, and a coil. Not Qi compliant, and no way to know what the firmware it's running is.
We've been troubleshooting the design and are running into very intermittent connection with our Qi 1.0 BPP Receivers (Rx) that are based around the BQ51013A. Unfortunately these Rx cannot be changed and have to be worked around. The EVM charges well and consistently locks to the Rx target, so the differences between the Qi versions wouldn't appear to be an obstacle.
The most telling behaviors we have are the protocol window of the 3.48 GUI between the two; once calibrated, the EVM throws no protocol window errors (prior to calibration, would throw an occasional QFOD error). Our Tx design, once calibrated and before, throws a variety of protocol errors including but not limited to: CONTROL ERROR TIMEOUT, BAD PACKET SEQUENCE, PACKET TIMEOUT, CHECKSUM ERROR, EPT RECEIVED, EPT OVER VOLTAGE, NO RESPONSE, and TX_OVER_CURRENT.
The Tx we designed indicates it identifies the Rx is stuck in reset according to the LEDs at short gap distances (<3mm), and attempts to connect unsuccesfully at greater gaps than 3mm.
With scope traces and measurements confirming the LC tuning, voltage and current at multiple points of interest in the desigh (LDO, DCDC boost, FETS, Coil) we're scratching our heads if we missed anything. It seems doubtful our firmware upload was incomplete, as the Tx does work occasionally, and the GUI monitors correctly, identifying the receiver and reporting the bridge voltage, etc.
We're currently looking into a VNA to analyze noise and harmonics.
I've been working off the following documents: STEVAL-ISB044V1 user manual, Qi protocol 1,2,4, the BQ51013A datasheet, and obviously our own schematics.
