BQ51003: RX Coil Tuning Issue

Matt Staniszewski

Part Number: BQ51003

Hi,

We are trying to use a smaller 15mm coil (Abracon AWCCA-15N15H06-C01-B and Wurth 760308101219) and we are having issues getting the BQ51003EVM to respond when we modified. We are using an off-the-shelf Anker TX coil (https://amzn.to/2TT4b3K) which works correctly when used with the EVM's reference RX coil (LED turns on for both TX and RX)

Attached are the calculated C1 and C2 values taking measurements as described in the BQ51003 specification for the Wurth RX coil. They are very similar to those of the EVM.

When we bring the Wurth RX coil + EVM near the TX coil, the TX LED turns on for several seconds. RECT voltage is sitting around 4.5-5.5V during this time. However, the RX LED does not turn on. I'm assuming there's a communications failure.

Does the BQ51003 have issues with smaller coils? Should we get a smaller TX coil? Is there a way to look at the communications?

Best,

Matt

BQ51003 Calculations - Wurth Coil.xlsx

over 5 years ago

0 Bill Johns over 5 years ago

TI__Guru* 75656 points

Hi Matt

Try increasing COMM 1 and COMM 2 capacitors, standard value is 22nF and they can be increased to 44nF.

0 Matt Staniszewski over 5 years ago in reply to Bill Johns

Intellectual 360 points

Hi Bill,

Thanks for the response. I added a 22nF to each COMM capacitor on the devkit to bring the total to 44nF. I got a very similar result; the TX coil powers up and I'm reading a voltage on RECT (closer to 5.5-6V now) but then the TX coil shuts off without the BQ51003 showing the charge is enabled.

Thoughts?

Best,

Matt

0 Bill Johns over 5 years ago in reply to Matt Staniszewski

TI__Guru* 75656 points

Hi Matt

Send a scope capture of the RECT pin voltage during start up and shutdown.

0 Matt Staniszewski over 5 years ago in reply to Bill Johns

Intellectual 360 points

Hi Bill,

Sure, see attached when powered up and attempting connection. The power-off looks very similar to the small pulse at the beginning of this trace. If I pull the RX coil away, the output decays to zero.

Best,

Matt

0 Bill Johns over 5 years ago in reply to Matt Staniszewski

TI__Guru* 75656 points

Thanks for the scope capture.

The RECT may not be reaching target voltage of 7V this could be due to communications error or system is running out of gain.

Check if the output turn on, OUT pin?

If the RECT does not reach target voltage output will not turn on. When OUT is on you should see a drop in the RECT voltage and the Comm Packets (CEP) will be at a 250mS rate. If system is having trouble tuning to target they will be at 30mS rate.

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BQ51003: RX Coil Tuning Issue