I'm just working on my own version of the wireless power transmitter and use your eval board schematics as a reference. Generally I consider the documentation of the eval board rather poor since there is e.g. no explanation how the circuits work, no oscilloscope figures, etc.
Now I would need a bit of consultation and clarification regarding the component selections around the comparators U11-B and U11-C. The thing that confuses me here is the hysteresis voltage compared to the threshold voltage of the comparators. The bias voltage at the positive terminal of the comparator is slightly abobe half supply (generated by the 10k-50R-10k resistor chain) and at the negative terminal sligthly below the half supply (generated by the same resistor chain). This makes about 8.25mV voltage difference between the therminals in steady state. On the other hand the hysteresis is implemented with 10k feedback resistor and 50R input resistor, which results in hysteresis voltage about two times this, i.e. 16.5mV. Now if the comparator sees a low going voltage (exceeding the threshold voltage) at it's input it will definitely toggle its output state, but due to the large hysteresis does it ever toggle back? Pls. explain if I have undestood something completely wrong or if there are some BoM updates for the eval board that would solve this apparent paradox.
Many thanks for you assistance!
I strongly recommend that you use our new and improved device the bq500210. The demodulation circuits you are asking about are replaced with digital demodulation circuits internal to the device.
Bill Johns, Applications Engineer
bqTESLA Wireless Power Products
Texas Instruments Inc
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