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TLA2024: Not able to read stable adc values with channel AIN0 & AIN1

akshay bansod
Prodigy 30 points
Part Number: TLA2024
Other Parts Discussed in Thread: ADS1015

Hello,

We are reading adc value for input ac voltage of 1.5v on channel AIN0 and 2.2v on channel AIN1 in differential mode. We are reading peak to peak values and verified it on oscilloscope.

  1. Not getting stable values when reading in differential mode, is there any conversion time taken by tla2024 as it seems we are missing the peak somewhere.
  2. Is it suggested to read differential reading between channel AIN0 & AIN1 as its not mentioned in datasheet.

Below are our configurations for TLA2024 if read in differential mode between channel 0 & 1:

setDataRate (TLA202x_RATE_3300_SPS);
setMux (TLA202x_MUX_AIN0_AIN1);
setRange (TLA202x_RANGE_6_144_V);
setMode (TLA202x_MODE_CONTINUOUS);

Thank You,

Akshay

  • 0
    TI__Guru** 113765 points

    Hi Akshay,

    The TLA2024 is a Delta-Sigma ADC and therefore includes an internal low-pass digital filter.  It is not clear what form/frequency of AC signal you are trying to measure, but it must meet Nyquist requirements and also not be limited by the digital filter.  Secondly, the differential measurement is not relative to GND but rather AINP relative to AINN and both inputs must meet the input voltage requirements for the ADC.  That is to say, the input voltage must be within VDD and GND for the ADC.  So if your source voltage goes below GND you will be in violation for the input range of the TLA2024.  1.5V and 2.2V are valid input voltages, but it is not clear by how much these voltages may deviate above or below these voltages.

    akshay bansod said:
    Not getting stable values when reading in differential mode, is there any conversion time taken by tla2024 as it seems we are missing the peak somewhere.

    To get a good representation of the waveform you must be capturing every conversion result and the maximum input frequency as per Nyquist is1600Hz for a 3300sps data output rate.  Most likely you are not capturing every conversion.  The ADS1015 has an ALERT/RDY function that can be used as an interrupt to make sure that every conversion is captured.

    akshay bansod said:
    Is it suggested to read differential reading between channel AIN0 & AIN1 as its not mentioned in datasheet.

    You can use any differential input combination that is given in the MUX configuration as shown in the register information in the datasheet and is also shown below.

    000 : AINP = AIN0 and AINN = AIN1 (default)

    001 : AINP = AIN0 and AINN = AIN3

    010 : AINP = AIN1 and AINN = AIN3

    011 : AINP = AIN2 and AINN = AIN3

    Best regards,

    Bob B