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ADS8568

Sushil Kumar1
Prodigy 80 points
Other Parts Discussed in Thread: ADS8568, ADS8598H

We want to capture harmonics of 3-phase motor line supply voltage & current simultaneously. From analysis point of view it would be better to have more number of harmonics at least 50th or more. Can you please suggest the suitable part for our application of 6 channel simultaneous ADC?

As we are looking for ADS8568 part with Analog Front End Typical Application of motor supply measure up to 20 harmonics in at 60-Hz power. Can we measure more number of harmonics with this? 

What is the key role and factors use to capture the harmonics using ADC and how do we calculate it? 

  • 0
    TI__Guru**** 168605 points

    Hi Sushil!

    Welcome to our e2e forum!  Sorry we missed your posting - this sounds like an interesting application!  The ADS8568 is one of our fastest/widest bandwidth simultaneous sampling ADC's.  Let us look around a bit to see if we have any tools/calculators to help you with this application.  Curious to know, why do you want to get to the 50th harmonic?

  • 0 in reply to Tom Hendrick
    TI__Guru 57336 points

    Hello Sushil,

    The ADS8568 is a good device to start your evaluation. If only 6 channels are required, you may power down one pair of channels using the PD_X bits in the CONFIG register. For example, PD_A = 1 will power down both CH_A0 and CH_A1. This will save some power vs. the 8-channel operation.

    The bandwidth that is required for 50 harmonics of 60-Hz power lines is only 3.06 kHz. The ADS8568 can easily support this, as long as the front-end drive circuit is designed appropriately. The amplifier circuit in the Applications Section can be modified to support this bandwidth by tuning Rf and Cf.

    Best regards,

  • 0 in reply to Ryan Andrews
    Prodigy 80 points

    Thanks for your comments!

    We have recently procure ADS8598H ICs & its evaluation board for testing. We would like to capture and do electrical signature analysis for 100th harmonics of 60-Hz 3-phase power lines, hence the required bandwidth would be 6.06 kHz.

    Since ADS8598H has internal AFE of 24 kHz bandwidth at -3dB power so will it be OK for our application? Also, considering the simultaneous sampling rate of 100 KSPS per channel, is that OK?

  • 0 in reply to Tom Hendrick
    Prodigy 80 points

    Thanks for your comments!

    Our application is to observe electrical signature of 3-phase power supply and do equipment health analysis based on supply harmonics pattern. 

    ADS8568 has external AFE with very wide bandwidth of 45 MHz which may not be required in our case. Please confirm us the minimum requirement of ADC -3dB bandwidth for 100 harmonics of 60 Hz power lines or cut of frequency. 

    Now we are using ADS8598H part, will it fulfil our application requirement? 

  • 0 in reply to Sushil Kumar1
    TI__Guru 57336 points

    Hello Sushil,

    The -3-dB small-signal bandwidth of the SAR ADC comes from the switch-capacitor input sampling stage. There is a known series resistance (200 ohms) plus the ON resistance of the switch (130 ohms) that forms a low-pass filter with the sampling capacitor. In the ADS8568, the sampling capacitor changes with input range. The +/-2*Vref range uses a 20-pF cap, which forms a low-pass filter cutoff of 24.1 MHz. The +/-4*Vref range uses a 10-pF cap, which forms a low-pass filter cutoff of 48.2 MHz.

    The bandwidth of the sampling circuit does not define the total bandwidth for the signal chain. This is purely the analog signal bandwidth that can theoretically pass through that R-C passive network when the input switches are closed. The total bandwidth for the signal chain will ultimately be limited by the discrete sampling rate of the ADC. The maximum sampling rate of the ADS8568 is 510 kSPS, which limits your bandwidth to only 205 kHz due to Nyquist sampling theorem. This max bandwidth is still more than sufficient to measure your 60 Hz fundamental plus the first 100 harmonics.

    Regards,

    Ryan

  • 0 in reply to Ryan Andrews
    Prodigy 80 points

    Hello Ryan,

    We agree with your comments. Thanks!

    Regards,

    Sushil