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MSP430F6779: When should I need a driver to drive the SDADC in MSP430F6779?

Sanzheng Yin
Prodigy 80 points
Part Number: MSP430F6779
Other Parts Discussed in Thread: THS4521,

      Now I am learning about emeter on EVM430-F6779-3 EVM. And I have some problems to understand the analog input part which belongs to  the hardware design.

in the 3.2 on page 6 of document slaa577g the schematic is :

my question is why there is no differential adc driver just like ths4521 to drive the SD24 in MSP430?

In my opinion ,if the current signal is a high frequency but not 50/60Hz, here may need a driver,

so  when should we need a driver to dirve the SDADC in MSP4306779? Pls give some analysis with foumulas and calculations ,thanks !

(I have know the input resistor of SDADC in the datasheet)

  • 0
    TI__Mastermind 49692 points

    Hello,

    Sanzheng Yin said:
    my question is why there is no differential adc driver just like ths4521 to drive the SD24 in MSP430?

    The THS4521 appears to be used in audio applications where the required sampling rates can reach up to 192kHz or more. Here, the MSP430F6779A is used in a metering application and can utilize its SD24 ADC module to measure RMS voltage and RMS current using the differential channels. Since the typical frequencies are 50 Hz or 60 Hz, a sampling rate of 4.096 kHz is adequate. The SD24 module also features an internal Programmable Gain Amplifier (PGA).

    Sanzheng Yin said:

    In my opinion ,if the current signal is a high frequency but not 50/60Hz, here may need a driver,

    so  when should we need a driver to dirve the SDADC in MSP4306779? Pls give some analysis with foumulas and calculations ,thanks !

    For the EVM430-F6779 design, the code configures the SD24 ADC to sample at 4.096 kHz - the sampling frequency (Fs). This is done by dividing the modulation frequency (Fm) by the over sampling rate (OSR). Here, Fm equals 1.048576 MHz and the OSR equals 256.

    Fs = Fm / OSR

    By changing the OSR to 128, you can increase Fs from 4.096 kHz to 8.192 kHz. You can read more about this on page 7 in the Implementation of a Three-Phase Electronic Watt-Hour Meter Using the MSP430F677x(A) app note.

    Regards,

    James

    MSP Customer Applications

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