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ADS1110, conversion issue

RAJESH KUMAR
Prodigy 90 points
Other Parts Discussed in Thread: ADS1110

Hi,

I am using ADS1110 16-bit A/D converter to convert differential and single inputs coming from different sources.

In differential input mode where the signals are generated across the thermal disk (thermal power converted to analog voltage), I don't see the digital data. Even analog input across the ADC i/p pins are changing (0.65mV/1.30mV/2.60mV). Here I could see the source which generates analog signal is passive source (Peltier module - it converts temp difference to voltage difference across its terminal).

However ADC is working perfectly when analog input is generated across a shunt resistor connected in series with photo diode.

In first case where source pwr/gnd is not connected to the pwr/gnd of the ADC, I notice the issue of not converting the analog values - is this happening due to common mode voltage spec is violated. Do we need signal conditioning prior to the ADC? Current circuit implementations look like below:

Please let me know why ADS1110 unable to convert the analog inputs, what is wrong with the circuitry?

Awaiting your valuabe inputs...

Thanks & Regards,

Rajesh

  • 0
    TI__Guru* 98025 points
    Rajesh,


    Are you saying that when you measure the thermal disc, you don't get the proper reading, but when you measure a shunt resistor, you do get the proper reading?

    I would guess that the problem is that the thermal disc voltage doesn't have a dc common mode voltage established. Even if you have a proper differential voltage, you still need a common-mode voltage that is within the range of the ADC. For the ADS1110, the input range is within GND-0.2V to AVDD+0.2V.

    I would try grounding the negative input of the thermal disc to see if this helps.


    Joseph Wu