BQ51003: Tuning resonant circuit for BQ51003

Hikaru Watanabe

Part Number: BQ51003

Hi,

We are trying to design a wireless charger using BQ51003.

I understand how to calculate C1 and C2 on Rx resonant circuit but I don't know how to measure resonant frequency and adjust an actual sample.

How did you measure resonant frequency and adjust C1and C2 for an actual sample of BQ51003 evaluation board?
I think C1 and C2 for evaluation board is not only calculated but also adjusted.

Thanks.

Hikaru.

over 2 years ago

0 Bill Johns over 2 years ago

TI__Guru 65646 points

Hello Hikaru

See data sheet "Series and Parallel Resonant Capacitor Selection" also see below FAQ .

Key is to measure the RX coil L in case with PCB and on TX Coil simulator to determinate Ls' values.

How Do I Select Capacitor Values for a Wireless Power RX Coil?: https ://e2e.ti.com/support/power-management/f/196/t/905132

0 Hikaru Watanabe over 2 years ago in reply to Bill Johns

Prodigy 20 points

Hello Bill.

Thanks.
I have understand to measure inductance.
Is Ls = resonance frequency?
I think C1 and C2 affect only resonance frequency.
How does C1 and C2 affect Ls?

Best regard.
Hikaru.

0 Hikaru Watanabe over 2 years ago in reply to Bill Johns

Prodigy 20 points

Hello Bill.

Thanks.
I have understand to measure inductance.
Is Ls = resonance frequency?
I think C1 and C2 affect only resonance frequency.
How does C1 and C2 affect Ls?

Best regard.
Hikaru.

0 Bill Johns over 2 years ago in reply to Hikaru Watanabe

TI__Guru 65646 points

Hello

Is Ls = resonance frequency? -- Bill J - No, Ls is the RX coil inductance in free space, value on data sheet.
How does C1 and C2 affect Ls? -- Bill J - Ls and Ls' are RX coil values and used to calculate C1 and C2.

0 Hikaru Watanabe over 2 years ago in reply to Bill Johns

Prodigy 20 points

Hello

Is following method of tuning resonance frequency correct?
1. Measure Ls inductance on PCB.
2. Calculate C1 and C2 using Ls value.

0 Bill Johns over 2 years ago in reply to Hikaru Watanabe

TI__Guru 65646 points

Hello

Is following method of tuning resonance frequency correct?
1. Measure Ls inductance on PCB. --- Bill J Yes, on PCB and on TX (un-powered) or TX simulator -- This will be the Ls' value used or C1.
2. Calculate C1 and C2 using Ls value. --- Bill J Yes, use Ls' for C1 then Ls for C2.

Note resonance frequency for C1 calculation is 100kHz and for C2 it is 1MHz.

Also see FAQ:

Coil frequently asked questions for wireless power RX: https://e2e.ti.com/support/power-management/f/196/t/942785
How Do I Select Capacitor Values for a Wireless Power RX Coil?: https ://e2e.ti.com/support/power-management/f/196/t/905132

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BQ51003: Tuning resonant circuit for BQ51003