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BQ51003: How to tune resonant capcitors value.

Prodigy 90 points
xiaoyan Yun

Part Number: BQ51003

Hello. 

I found a equation on bq510003 datasheet on page 27.  if use fs=10KHz, fd=1MHz, and Ls value is fixed. therefore C1, C2 will be worked out. 

But I use EVM parameter Ls=10uH to work out C1,  get C1= 3900000F. it doesn't match EVM C1=68nF + 68nF +47nF = 183nF. 

Could you please check it and give me a explaination. thank you!

Any side, I didn't find the equation on TX chip datasheet (bq50002A). how to work out TX resonant capcitors?  

Prodigy 90 points
xiaoyan Yun
  • Mastermind 27730 points
    Bill Johns
    Hello
    On data sheet page 27 equation 6 shows fs = 100kHz and fd = 1MHz. I do not see fs=10kHz.

    For C1 calculation the Ls' value should be used. This is measured with the coil mounted on a TX coil simulator , Fig 34.
    Ls' will be higher than free space inductance Ls used for calculation for C2 (Cd).

    For BQ51003 the Ls' value measured 13.5uH, this will calculate a value for C1 187nF, in the ckt C1/C2/C3 is 68nF/68nF/47nF = 183nF.

    The TX side is set by WPC standard for A11 TX. The L value is set at 6.3uH and resonant caps are set at 400nF.

    Best Regards,

    Bill Johns,  Applications Engineer

    Texas Instruments Inc

    Dallas, Texas

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