About resonant capacitors of the BQ51221

user4377449

Prodigy 30 points

Other Parts Discussed in Thread: BQ51221

Dear TIers,

I saw a set of formula in the BQ51221, but the quantities are not defined, so what does mean about fs, fd, Ls' and Ls?

And what is the value of your recommend?

Thanks and regards!

Chen.

over 8 years ago

0 user4377449 over 8 years ago

Prodigy 30 points

I am so sorry. My screenshot is not shown. The equation is at the "10.2.1.2.9 Series and Parallel Resonant Capacitors".

0 Wenjia Liu over 8 years ago in reply to user4377449

TI__Expert 7730 points

Ls refers to the RX coil inductance and it is measured in free space with RX battery. Ls' is measured on WPC stack with receiver coil spacing and battery.

The Ls/Ls' value is different from coil to coil and need to be measured to calculate Cs and Cd. Please use the below tool for calculation.
www.ti.com/.../sluc566

Thanks,
Wenjia

0 user4377449 over 8 years ago in reply to Wenjia Liu

Prodigy 30 points

OK! I get it!

Thank you very much!

Chen.

0 Bill Johns over 8 years ago in reply to user4377449

TI__Guru 65746 points

Moved from FAQ section:
Hello TIers,

In BQ51221A, I saw the AC1 pin connect a series capacitance C1. So what is the function of this capacitor(C1)?

0 Wenjia Liu over 8 years ago in reply to Bill Johns

TI__Expert 7730 points

The series cap C1 (Cs) and the parallel cap C2 (Cd) make up the dual resonant circuit with the receiver coil. The value of the two caps must be calculated according to the WPC v1.1 specification. You can use the same design tool to calculate the value.

Thanks,

Wenjia

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About resonant capacitors of the BQ51221