BQ51003: Tuning C1 and C2 to use a different coil

Greg Levesque

Part Number: BQ51003
Other Parts Discussed in Thread: TIDA-00318, BQ25120

I have an application for the BQ51003 that requires the use of a rectangular coil (TDK WR221230-36M8-G) and I'm have trouble with establishing a power transfer.

The values L is slightly different from the reference design coil (TIDA-00318) 27.9uH vs 27uH.

The datasheet provides and example on how to tune C1 and C2 given a values for Fs and Fd yet when I do the math with the reference design values the frequency numbers don't match the frequencies provided in the datasheet, Fs = 100kHz, and Fd = 1MHz.

My questions are:

- What should I use for Fs and Fd to calculate C1 & C2?

- Is the rectangular coil a problem in general, would one expect degraded performance with respect to a round one?

- Does TI recommend any particular Qi charger solution(s) that works with smaller RX coils?

Thank you

-Greg

over 4 years ago

0 Bill Johns over 4 years ago

TI__Guru 65836 points

Hi Greg

We have not tested the WR221230-36M8-G (12mm X 22mm). The TIDA-00318 22mm coil will work but smaller coils have lower coupling and have caused problem.

Recommend tuning C1 and C2 with the higher L value. Note that coil L (Ls') for C1 should be measured in the case and on TX.

What current will you be operating at?

0 Greg Levesque over 4 years ago in reply to Bill Johns

Prodigy 20 points

Thank you for the information Bill, we are trying to charge a battery which is connected to the TI BQ25120 @90mA.

Thank you for clarifying the L measurement, does that imply that Fs = 100kHz, and Fd = 1MHz. for equation(s) 6 in the datasheet?

0 Bill Johns over 4 years ago in reply to Greg Levesque

TI__Guru 65836 points

Hi Greg

""does that imply that Fs = 100kHz, and Fd = 1MHz. for equation(s) 6 in the datasheet"" -- Bill J -- Yes.

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BQ51003: Tuning C1 and C2 to use a different coil