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BQ500211 Oscilloscope load

Jason Luzinski
Prodigy 100 points
Other Parts Discussed in Thread: BQ51003EVM-764

Hello,

I am trying to measure the power being dissipated in the Tx coil.  I have connected an oscilloscope between TP1 and TP2 to measure the peak to peak voltage across the Tx coil and then use the resistance of the coil to find the power.  However, I notice that when I attach a the oscilloscope to working system, the input current into the system increases, which means that system efficiency decreases.  Is the oscilloscope placing an extra impedance on the PA/Tx coil and will it effect my power measurement?  Can the TP I_Sense be used to measure the coil power?

Thanks,

Jason

  • 0
    TI__Genius 14890 points

    Jason,

    Another post I missed.  My apologies.

    I expect that what is happening is adding the scope probe changes the resonant frequency of the circuit.  I took a few measurements to illustrate the change.  This was tested with a bq51003EVM-764 at 200mA (about 1W).  Position 1 and Position 2 are different placements of the RX on the TX.

    Parameter No scope, position 1 No scope, Position 2 Scope, Position 2
    VIN (V) 5.011 5.010 5.007
    IIN (mA) 340 350 380
    Freq (kHz) 171.1 155.6 133.3
    PIN (W) 1.704 1.754 1.903

    Regards,

    Dick