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50/60 HZ Rejection

Mateus
Prodigy 110 points
Other Parts Discussed in Thread: LMP90100, PGA280, ADS1248, ADS1259, ADS1258

Hello all,

I need some help about 50/60Hz rejection of ICs ADS1248, LMP90100 and PGA280 + ADS1259. According to datasheets:

ADS1258 ->  -71/-74db (50/60Hz+-0,3Hz) and  -66/-68db (50/60Hz+-1Hz) at 20 SPS (Table 9)

LMP90100 ->  more than -100/100dB  (50/60Hz+-0,3Hz) and  more -90/100 (50/60Hz+-1Hz)  at 13.42 SPS (Figure 7).  

PGA280 + AS1259 -> only figure 42 provide some information, but  is no so clear values for 50/60+-0,3HZ or 50/60+-1Hz.

Please someone confirm values versus data rates of each component, specially about LMP90100 and PGA280+1259?

  • 0
    TI__Guru**** 181871 points

    Hi Mateus,

    Your question actually covers a couple different product groups so we'll try to get you a consolidated answer by COB on Monday.  In the meantime, can I ask what sort of application you are planning?  Are you using all of these parts in your project or are you simply trying to make a decision on which part to use?

  • 0 in reply to Tom Hendrick
    Prodigy 110 points

    Hi Tom,

    I'm simply trying to make a decision. My use is a RTD application and I have already woked with PGA280+ADS1259. Because of cost, ADS1248 or LMP90100 seems to be a good choice, even with more than 4 ports RTD.

    Regards,

    Mateus.

  • 0 in reply to Mateus
    TI__Mastermind 43915 points

    Hi Mateus,

    For the ADS1259 - The actual attenuation at 50/60Hz is going to be dependent on the exact master clock frequency. Assuming that you are using the internal oscillator which is closely matched to 7.3728MHz, the attenuation should be greater than 100dB at 60Hz with about 70dB attenuation typical within +/-1Hz for the SINC2 filter at 60SPS. Table 4 and Figure 42 is the collateral which we have detailing the digital filter. I can see if we have any more information regarding any simulation results on the digital filter if interested.

    Regards,

    Tony Calabria

  • 0 in reply to Tony Calabria
    TI__Intellectual 1635 points

    Hi Mateus,

    My response to your question is on the same as Tony's response.  The LMP90100's 50/60 Hz also depends on what output data rate (ODR) the device is running.  And if you are using the external clock instead of the internal clock, then the ODR also depends on the value of your extenal clock.

    You can refer to section 16.1.7 of the LMP90100 datasheet (http://www.ti.com/lit/ds/symlink/lmp90100.pdf) to see the filter response at different data rates, as well as how to calculate your ODR if you are using an external clock source.  For example, if you look at figure 6, then you can see that running the device at 13.42 SPS means you'll get about 103 dB at 60 Hz and around 97 dB at 50Hz. 

  • 0 in reply to AmyLe
    Prodigy 110 points

    Thanks Tony and Amy.