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single ended configuration of ADS1248

Ramakrishna Nidmarty
Prodigy 50 points
Other Parts Discussed in Thread: ADS1248

I need to connect AIN0 - AIN1 as differential input, and AIN2 to AIN 7 to single ended inputs. when I am measuring input connected to AIN2, how do I config MUX0 reg for say AN2 as single ended input. All others are connected to the circuit with common ground and I am using +2.5V and -2.5V to power the AVDD and ASS

  • 0
    TI__Guru* 97585 points

    Ramakrishna,


    For the ADS1248, single ended measurements are measured with reference to one of the inputs.

    As an example, you could use one measurement as AIN0-AIN1, but you would need to choose one of the other measurements as the second input. So for the remainder of the inputs, you could measure every other measurement with reference to AIN7. AIN2-AIN7, AIN3-AIN7, AIN4-AIN7, AIN5-AIN7, and AIN6-AIN7 would be selected with the same MUX0 register. There isn't a common input that can be set up with the ADS1248.


    Joseph Wu

  • 0 in reply to Joseph Wu
    Prodigy 50 points

    Thanks.

    But that means I need to connect say AN7 physically  to ground (confirm this) and measure AIN2 as +VE AND AIN7 AS -VE , and I should write to MUX0 register  27 HEX.

    Should Internal voltage reference appear  on REFOUT and REFCOM pins all the time, irrespective of  VREFCON1:0 bits of MUX1 register and these bits only control reference selection to reference multiplexer, or by VREFCON1:0  setting them to 01 to make reference always on , and  please clarify if  this internal reference can appear on REFP0 and REFN0 pins as per figure 32 of data sheet by REFSELT1:0  bits setting to 11 of MUX1 register

  • 0 in reply to Ramakrishna Nidmarty
    TI__Guru* 97585 points

    Ramakrishna,



    That is correct, you would connect AIN7 physically to ground. There are no other internal connections to the analog input pins. To select AIN2 and AIN7, you would have MUX0 set to 17h (not 27h).

    The reference only appears on REFOUT to REFCOM as long as the internal reference is turned on. So if it VREFCON is 00h, voltage does not appear, or if VREFCON is 10h or 11h and the device is shutdown, or if the START pin is low, the voltage does not appear. If there is a lot of capacitance on REFCOM, it may take time for the reference to settle to its final value. In that event, you could just keep the reference on.

    To use the internal reference for ADC conversions, the REFSELT can be set to 10h which will select the reference, or set to 11h, where the internal reference is selected and the reference is set to REF0P and REF0N so that the reference appears at those pins.



    Joseph Wu