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pga280+ads1255

Nestor Closa
Prodigy 30 points

Other Parts Discussed in Thread: ADS1255, PGA280, ADS1259, ADS1232

Hello,

I'm going to design a high-end weight indicator.

The excitation voltage for loadcell is 10V and data rate from 10 to 500 sps.

I select one PGA280 for signal and another for remote sense and ADS1255.

There is another option to get the best level of noise and performance?

 

Best regards,

Nestor

 

  • TI__Mastermind 43915 points

    Hi Nestor,

    You may want to look into the PGA280 and ADS1259. That specific ADC was designed to be mated with the PGA280i includes single cycle settling and has 50/60Hz rejection at 10SPS. You will have an internal reference voltage eliminating the need for external components with the ADS1255.

    As for noise and performance - What are you looking for? Depending on the PGA gain and ADC data rate, your ENOB and input referred noise is going to change. If you are using this in a DC weigh scale application, slower data rates may be beneficial as it provides a lower nyquist cutoff point decreasing your overall noise.You can look at Table 1 on page 13 of the ADS1259 data sheet to get some numbers for comparison.

    Regards,

    Tony Calabria

  • in reply to Tony Calabria
    Prodigy 30 points

    Hi Tony,

    I was looking for single cycle settling and 50/60Hz rejection at 10sps. I don't need the internal reference voltage since the measurement should be ratiometric and I must put another amplifier for the remote sensing function (10V). I chose ADS1255 instead of ADS1259 because the noise-free resolution is better at 500sps.

    I use ADS1232 G=128 10sps +5V excitation voltage and with a moving average of 8 I get about  +/- 200,000 noise-free counts at 2mV/V. In this new model, with an excitation of 10V and an external amplifier, I hope to get at least +/- 500,000 noise-free counts at 10sps 2mV/V (20mV). I don't know if the noise from the PGA280 can restrict that. Full-scale must be at least +/- 36mV.

    Thanks,

    Néstor

  • in reply to Nestor Closa
    TI__Mastermind 43915 points

    Hi Nestor,

    As I understand it, you want to go from currently using the ADS1232 to now using a faster ADC that you can run at 500SPS. As you go to a faster ADC, you will see an increase in your input referred noise (decrease in ENOB). As I understand it, you want to have +/-500,000 noise free counts which is a total of 1,000,000 noise free counts. If my calculations are correct, that is equivalent to 20 noise free bits of resolution. That looks like it is going to be difficult, especially as you start adding gain to your system. Looking at the ADS1255 data sheet (page 13) at 500SPS, your noise free bits are exactly at 20 bits. As you increase the gain, the noise free resolution decreases. The same will hold true if you include a PGA280 when you take into the account the noise from that. What gain are you looking to put the ADS1255 / PGA280 in? A gain of 128 again?

    Regards,

    Tony

  • in reply to Tony Calabria
    Prodigy 30 points

    Hi Tony

    No, I expect to have +/- 500,000 noise free counts but at 10 sps with +/- 20mV, the noise will obviously increase with 500 sps. As AVDD from ADS1255 is 5V and I want to excite the bridge with 10V to improve the relation signal-noise, I can't connect directly the input of the A/D to the bridge and I must use an amplifier, I guess with G=128 and A/D G=1

    Regards,

    Néstor