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ADS7828: ADS7828E

Dharmesh Joshi
Expert 1815 points
Part Number: ADS7828
Other Parts Discussed in Thread: ADS7830, ADS1115, ADS112C04

Hi

We are thinking about using the ADS7828E ADC to measure the voltage of electrochemical air sensors. These sensors generally output voltage below 1V.

Is there any other ADC with the ref that is close to 1V?

Each sensor will have 2 Chanel voltage output, there will be 4 sensors, therefore 8 chanels will be required.

The ADC needs to be i2c ?

Can the ADC work on simple 2 layer PCB?

  • 0
    TI__Mastermind 22950 points

    Hi Dharmesh,

    The ADS7830 might be a part to look at. This part offers the option to provide an external reference. However, the lower the reference, more noise will be introduced and this can cause some error. We have another option in the ADS1115 but this is only a 4 channel device and I am afraid you would need two for 8 channels. With the ADS1115, there is an internal reference and there are programmable full scale range settings that vary from +/- 256 mV to ~ +/-6.144V. 

    A 2 layer board should be fine but it really just depends on your system. Just ensure you are practicing good PCB layout techniques Slight smile. Some of our newer data sheets offer some layout guidelines as well so that is something to take note of. 

    Regards,

    Aaron Estrada

  • 0 in reply to Aaron Estrada
    Expert 1815 points

    Dear Aaron

    ADS1115, looks interesting as I reduce the ref voltage to about 1V. But the availability of the component will be an issue. 

    Why is it that lower the ref voltage, more noise will be introduced? 

  • 0 in reply to Dharmesh Joshi
    TI__Mastermind 22950 points

    Hi Dharmesh,

    When the reference voltage is reduced, the LSB is also reduced. When the LSB is reduced, errors such as Offset and Gain error will increase in terms of LSB size. The inherent noise of the ADC also changes with LSB size and will increase when the LSB deceases. This is noted in the ADS7830 data sheet. 


    Regards,
    Aaron

  • 0 in reply to Aaron Estrada
    Expert 1815 points

    Hi Aaron

    Let me explain my current setup. I am using a microcontroller with ADC. The ADC is set up in 12-bit with 1V internal reference. The sensor I am measuring output voltages on two ports, and the general voltage is about 03-0.4V. My main PCB has access to only 2 ADC ports.

    In regards to the LSB error etc, this makes sense, as with 1V reference each setup is also much less.

    Therefore I am considering using a 2.5V reference with 16 bit ADC.

    Is there a 16-bit solution with an internal 2.5V, controlled by i2c?

    Is there also any device, that will also continuously keep reading each ADC channel and preforming an average, so that when I perform an i2c read i am getting a averaged valus, so that i do not need to poll the i2C for each adc channel to achive an averaged value?

  • 0 in reply to Dharmesh Joshi
    TI__Mastermind 22950 points

    Hi Dharmesh,

    Using our parametric search, it looks like we only have a few delta sigma ADC options with the ADS111x/ADS101x family being the majority. This family includes the ADS1115/1015 that I mentioned above. The ADS112C04 is also an option. However, these parts won't be capable of averaging data over multiple channels. The delta sigma ADC's will oversample and average the data but that will be for 1 conversion and again, won't be capable over multiple channels. 

    You mentioned that availability may be of concern. We do have a few ADS1115DGS available and quite a bit more of the ADS112C04. What type of quantities are you looking to purchase? I understand if you cannot disclose this but I would like to get a general idea to see what we might be able to do. 

    Regards,
    Aaron

  • 0 in reply to Aaron Estrada
    Expert 1815 points

    Hi Aaron

    Thanks

    What is the advantage of a delta-sigma ADC in comparison to a standard ADC?

    So that I understand the operation correctly when I request i2c read it will take multiple samples and produce an average? And this will be repeated for each channel. What i would like to avoid is producing maybe 100 i2c read calls and then doing to averaging on my microcontroller. 

    Initially, we aim to produce a qty of 10-15, for our client as a trial, then we will progressed to a production qty.

  • 0 in reply to Dharmesh Joshi
    TI__Mastermind 22950 points

    Hi Dharmesh,

    Using SAR vs Delta-Sigma is really dependent on your application and requirements. The delta-sigma ADC's are usually higher resolution but lower speed. There is increased latency due to the internal digital filter. SAR ADCs offer lower latency and higher speed but are generally lower resolution.

    We have a video series on our ADCs and I have provided a link below. The video discusses the differences between SAR vs Delta-Sigma ADCs as well as how the different architectures operate. 

    https://training.ti.com/ti-precision-labs-sar-delta-sigma-basic-operation?context=1139747-1140267-1128375-1147914-1147913

    Regards,

    Aaron Estrada