Other Parts Discussed in Thread: BQ50002A
We made a custom charger which is almost a complete copy of the bq500511A application schematic from the datasheet. We only changed the coil to match the RX coil we are using. The new TX coil is the WT151512 from TDK. We experience some issues with the device heating up considerably which causes the charging to stop after some time due to the automatic turn off with the NTC becoming too hot. We did some resonance measurements on both our own, custom charger (with the bq500511A) and the bq500212AEVM board. These resulted in following graph:
The curves on top show almost no loss, which is what we expect. The refcharger is the bq500212AEVM board, the sensor is our TX and the charger brd is our own custom charger (copy of bq500511A application schematic). With our charger, there is a clear loss which is already -3.5dBm at 100kHz. We noticed that when we removed the snubbers, the curve was almost exactly as the curve from the refcharger.
As the only thing we changed is the TX coil, should the snubber parameters also be adapted to the new coil?
Why are there snubber circuits used? The bq500212AEVM does not use these.
Could this loss have something to do with our device heating up? When I removed the snubbers, I did not see significant decrease in heating up, but maybe the snubbers can help when they are retuned?