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ADS1248 or 1243

TI Lady
Genius 4025 points
Other Parts Discussed in Thread: ADS1243, ADS1248, ADS1231, ADS1232, ADS1220

I am looking at the ADS1243 or ADS1248 for use in a weigh scale. The question is how low can we get the power for 2 SPS on 4 half (or full) bridge Load Cells. I do want to have some over sample / decimation to improve noise but I think we can get away with 8 or 16. I will be running this on 2500 mAhr rechargeable batteries and would like to get 3 to 6 months out of a charge. By the way there is WIFI on this so expect 4 to 6 < 1min transmissions per day at say 250 mA on average. If we could get the average current down to 300uA I think it could be accomplished. We are using a MSP430 as the controller so power is pretty low here.


Is this possible?
Thanks,

  • 0
    TI__Guru* 98025 points

    Hi,


    Normally, I'd recommend the ADS1232/34 or the ADS1231 for weigh scale applications. While the noise is low, I think the supply current is a bit high for you.

    Some of this depends on the data rate and PGA gain that you need, but both the ADS1248 and the ADS1243 get you in the ball park for the current consumption. The ADS1248 is a bit higher for the minimal current (I think the minimum is just north of 400uA) while the ADS1243 is lower (at about 300uA with PGA=1 and buffer off). Just consider the total current of both the analog and digital currents combined. If you outline some of your noise and data requirements it might help to figure out what might work best for you.


    Joseph Wu

  • 0
    TI__Guru* 98025 points

    Hi again,

    Another possibility that might suit your needs is the ADS1220. While the current is low, depending on the features used, it only has 4 inputs. I thought I'd add that for your consideration.

    Joseph Wu

  • 0 in reply to Joseph Wu
    Genius 4025 points

    I was hoping to be under 300 uA for the analog / MCU portion of the design in it's entirety. I took the WIFI out of the equation already.

    As for noise and data requirements we are going to sample at about a 0.5 hertz rate (once every 2 or so seconds) until there is activity. The sampling frequency will then go up to about 2.5 samples per second with some oversampling to be included. This activity will be monitored until a stop condition is met which should be within 2 min. Then the scale will go back to 0.5 samples per second. We will be in the lowest sleep mode possible in between sampling events and during the active data collection time.

     As for noise performance we are using 4 load cells with about 2 mV / V full scale sensitivities in half bridge configuration. we could use full bridge if this would be a benefit. Resolution should be on the order of 120 nV / cnt and noise performance better than 37 nV / Hz^-2  10 to 100 Hz.

    THanks for the speedy help!!