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ADS7841-Q1: How to understand and properly retrieve data from differential pair inputs.

Part Number: ADS7841-Q1
Other Parts Discussed in Thread: ADS7841


I am working on a differential input accelerometer sensor, specifically the Dytran 7500 (Operating Guide). I was successfully gather the data for the single-ended configuration. However, I want to use the Differential mode of the ADS7841-Q1, I wonder what is the sequence I should use to capture the data from the +IN and -IN?


My current sequence of getting the data is as below.

1. Select the chip

2. Send in the control byte (0x93) - I am using CH0 and CH1 as the differential pair.

3. Send in dummy byte (0x00) to generate clock

4. Getting the first 8 bits of converted data

3. Send in dummy byte (02x00) to generate clock

4. Getting the second 4 bits of converted data

7. Deselect the chip

The sequence above worked fine for single-ended input but for differential, the data doesn't make sense as it jump between two different distinct values.

I assume the jump between values is the read in of either +IN or -IN. What would be the recommended sequence to getting the correct value?


Secondly, I am a bit lost when reading the data sheet of ADS7841-Q1 regarding the analog input, the datasheet stated

When the converter enters the hold mode, the voltage difference between the +IN and –IN inputs (as shown in Figure 2) is captured on the internal capacitor array. The voltage on the –IN input is limited between –0.2 V and 1.25 V, allowing the input to reject small signals that are common to both the +IN and –IN input. The +IN input has a range of –0.2 V to VCC + 0.2 V. The input current on the analog inputs depends on the conversion rate of the device. During the sample period, the source must charge the internal sampling capacitor (typically 25 pF). After the capacitor has been fully charged, there is no further input current. The rate of charge transfer from the analog source to the converter is a function of conversion rate.

How would that bold sentences taken into account of the Dytran input behavior (see picture below)?


Thank you for reading.



  • Hello Alex,

    You are sending the sequence. This device allows for the negative pin to be set above or below ground, (-0.2V to 1.25V) as you have noted, this is primality to help with common noise. This device though is older and back at that time, the abilities this device has might have been considered differential. But now a day, differential would require a wider span on both input pins.

    This device will not be able to be paired with the accelerometer if you try to read both positive and negative terminals as differential. You could read each terminal in single ended mode and then in data processing subtract the two readings. Ultimately anything you do will be a band-aid solution.

    I would suggest changing to a differential device. I did a quick parametric search and found 4 results, but you can change the filters on the left to meet your requirments. The ADS7223 looks to be a good fit, I can also help you on your seach. I will point out that the ADS7841 will not appear as it is classified as a single ended device in the paramteric search.

     If you would like more information on ADC input types, we have a video: PL ADSs: SAR ADC Input Types as parts of our Precision Labs Tutorial Videos

    Regards, Cynthia