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ADS131E08: nPWDN nRESET pin usage and single ended input configuration

Nico Niemeyer
Prodigy 10 points
Part Number: ADS131E08
Other Parts Discussed in Thread: ADS131M08

Tool/software:

Hello,

I am currently developing a data acquisition system which is based on ADS131E08 ADCs. I have two questions:

1. I will not use the nPWDN and nRESET pin, because to save energy in our application the power supply will be completely disabled.
How should the two pins be connected in this case? Can you let them float or do they have to be pulled against DVDD and if so can you do this directly or do you have to use an external pullup resistor?

2. The second question concerns the input configuration for single ended signals.
In our application only single ended signals in the 0-5 V range are used. As I understand the data sheet, it is not possible to connect the negative input to GND as is the case with the ADS131M08 due to the common mode input range? I would therefore have to connect the negative input to a 2.5V potential and could then also cover the full dynamic range of the ADS131E08 with my 0-5V input signal?

I would like to thank you in advance for your help :-)

  • 0
    TI__Mastermind 46560 points

    Hello Nico,

    1.  You should tie both of these pins to DVDD in this case.  Option; If you prefer some flexibility for hardware debug, you can tie each of these pins to DVDD using a 10kOhm pull-up resistor on each pin.  Also note that since you are not using the nRESET pin, after power-up, you should send the RESET command to properly initialize all registers.  See section 11.1 of the datasheet and Figure 65.

    2.  For a single ended input, you would need to connect INxN to mid-supply, or 2.5V.  However, you will have additional headroom limitations due to the internal PGA common mode range.  In the case of INxN=2.5V, AVDD-AVSS=5V, INxP will be limited from 0.3V up to 4.7V.  Any voltage outside this range will result in measurement errors.  In order to support 0V to 5V, you will need to level shift the input using a resistor network.  Below is one example on how to do this.

    Using the above resistor values, the ADC will see a differential input voltage of -2V to+2V for a 0V to 5V input.  If you need high input impedance, then a buffer amplifier with a negative supply voltage will be required to support 0V input accurately.  Although a rail-to-rail IO amplifier can support inputs down to 0V with a single supply, the output of the amplifier will not be linear for output voltages less than about 0.1V.  In this case, to support 0V to 5V, the amplifier would need to be operated from about -0.2V and +5.2V supply rails.

    Regards,
    Keith Nicholas
    Precision ADC Applications