AD7609 Output Precision

Hai all,

           We have selected AD7609 for a high precision output conversion as it is an 18-bit ADC.

Using Eval-AD7609EDZ, we are getting only 12-bit precision when Interfaced in serial with a TMS320F28335 using Serial Peripheral Interface(SPI). We cannot go for Over-Sampling, because OS adds delay in Processing and our system is time constraint.

  • We have connected TMS320F28335 and ADC using a bus connector with a length of about 5cm. (Image is attached)
  • SPI frequency set to 6MHz.
  • Range of ADC used is +/- 10V.
  • Vdrive = 3.3V and Vcc = 5V, both supplied from SMPS
  • Analog Input to Channel 1 from a 24V Battery and all other channels(2-8) connected to GND.
  • DB7 pin is used for data capturing of 8-channels by providing 144 Clocks and DB8 pin is left pen.
  • DB0-DB6 and DB9-DB17 are connected to GND.

Also tested in parallel Interface with TMS320F28335 and the results are 12-bit only precision same as Serial Interface.

Please answer these questions and help me improve my AD7609 Outputs with a better precision & accurate output:

  1. Can AD7609 provide more precision output than 12-bit? If yes, What is the maximum precision of AD7609 we can expect?
  2. Is there any additional care to be taken other than the information provided in data sheet for traces.
  3. How to take Differential Non-Linearity = -0.99/+2 LSB's,

                          Integral Non-Linearity = +/-7.5 LSB's

                          Total Unadjusted Error = +/- 10 LSB's into consideration for ADC results as described in Page 4 of AD7609 Data-sheet

Please reply as soon as possible.

Thankyou,

Komali.

Parents
  • 0
    •  Analog Employees 
    on Nov 9, 2014 10:28 PM

    Hi, Komali.

    Apologies for the delayed response. What do you mean by 12-bit performance - is this ENOB, p-p noise free bits, code spread or TUE?

    May I ask why you chose the AD7609 for your application? It has true differential inputs and its performance is optimized for ±5V and ±10 V input conditions. You lose  a bit of resolution when you use it  as single ended. It is calibrated for differential operation so by operating the part in SE configuration we cannot guarantee THD or INL. You may opt to use the AD7608 which accepts single ended inputs if it also fits your other considerations.

    Regards,

    Karen

Reply
  • 0
    •  Analog Employees 
    on Nov 9, 2014 10:28 PM

    Hi, Komali.

    Apologies for the delayed response. What do you mean by 12-bit performance - is this ENOB, p-p noise free bits, code spread or TUE?

    May I ask why you chose the AD7609 for your application? It has true differential inputs and its performance is optimized for ±5V and ±10 V input conditions. You lose  a bit of resolution when you use it  as single ended. It is calibrated for differential operation so by operating the part in SE configuration we cannot guarantee THD or INL. You may opt to use the AD7608 which accepts single ended inputs if it also fits your other considerations.

    Regards,

    Karen

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