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ADS1110: questions of ADS1110 converting

BingXie
Intellectual 360 points
Part Number: ADS1110
Other Parts Discussed in Thread: ADS1115

hi, i have couple questions when using ADS1110 convertor.

1. seems like there are no Sample & Hold funtion for this devices, so what happen if the intput voltage change when converting?

the current setting is PGA=8 and DR=15 SPS 16 bit converting.

how long will this devices take to converting the analog voltage to digital number?(PGA=8 and DR=15SPS 16 bits)

2. about offset error

i need some detail information of how we deal with this offset error.

my input voltage range is about -0.5mV ~ 35mV, 0.4mV offset is somthing that i can not ignore.

So , is the error are fixed value for each individual components? like can i set a number in my CPU to corrector 0 point or i have to calibrate the ADC when power up?

3.What happen is Vin+ and/or Vin- goes higher than Vdd?

the analog sensor are working @ 5V but ADS1110 been set to working at 3.3V which will be easier to talk to CPU via IIC.

4.is there are CMRR and PSRR value can be guaranteed? since it's a differentail input signal and may have noise on 3.3V power source( like IIC clock and data line).

Thanks and best regards,

  • 0
    TI__Guru* 93635 points

    BingXie,


    There are quite a few questions here, so I'll just answer them as asked.

    1. This device does not have a sample-and-hold type circuit on the input. This device is a delta-sigma type of device and the input is sampled many times to make a single conversion data. During the entire data period of 66.7ms (15SPS), the device is sampling at the modulator rate. With a data rate of 15SPS and a modulator rate of 275kHz, the device takes about 18000 input samples to make a single output data from the ADC. The output data is basically an average of the measurements during the entire data period.

    2. I don't have much detail about the offset voltage. I believe that you would need to calibrate the offset from part to part. There will be changes in the offset from temperature and power supply and we describe some of that in the datasheet in the Electrical Characteristics table and typical curves.

    3. The VIN+ and VIN- should not go beyond the supplies. If you look at the Absolute Maximum table on page 2 of the datasheet. If any input goes below -0.3V or above VDD+0.3V, you may damage the device. If you want to measure a voltage that goes to 5V, then you should run the VDD at 5V, or you may need to attenuate the input signal. Also, because this device has an internal reference of 2.048V, the (AIN+)-(AIN-) should be smaller than 2.048V.

    4. CMRR and PSRR are not guaranteed. We only list a typical value for those parameters.

    I would note that you may need more precision and accuracy in your measurement. If you need that, I would recommend a different device. The ADS1115 is similar and may be more appropriate for your application.


    Joseph Wu

  • 0 in reply to Joseph Wu
    Intellectual 360 points

    Thank you for your help,

    All my questions been answerd.

    Thank you and best regards,