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BQ50002A: Charging drops in / out with BQ50002A/BQ500511A

Part Number: BQ50002A
Other Parts Discussed in Thread: BQ500511A,


We have implemented a custom charge transmitter PCB using the BQ50002EVM-607 reference schematic and design files. We also have a custom PCB receiver implementation of the BQ51003BY based on:

Happy to share Schematic and / or Altium files if this would help. Our transmitter is using the 'A' versions - BQ50002A / BQ500511A.

Our receiver is using this coil: Wurth 760308103202 (12 uH). The charge transmitter is using the same coil as the reference design: Wurth 760308111 (6.3 uH).

Our receiver is working perfectly when used with the BQ50002EVM dev kit transmitter (beep after ~500ms, green LED flashes, and transmitter draws ~300mA from 5V supply). Also the BQ50002EVM dev kit receiver is working with our custom charge transmitter. We have around 3mm to 5mm separation between the coils.

However, when we try to charge our custom receiver on our custom transmitter, we observe the following:

  1. It takes much longer to start, around 2 - 3 seconds before the green LED on the transmitter starts to flash.
  2. After startup the transmitter draws a steady ~300mA from a bench PSU (at 5V) for about 1 second, and then the charger input current starts to ramp up to ~1A within about a second.
  3. The charger input current then drops quickly to ~100mA and the green LED turns off.
  4. After a couple of seconds the process starts again.

Occasionally the red LED starts to flash, and charging stops completely. After a while it sometimes restarts the procedure above.

We have already tweaked and tuned the ILIM and FOD thresholds (also resonant capacitors), but it did not seem to make any difference.

Any guidance for troubleshooting would be very greatly appreciated.