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ADS131A04: Data acquisition values fluctuate under specific conditions.

user6205274
Prodigy 30 points
Part Number: ADS131A04

Subject: Data acquisition values ​​fluctuate under specific conditions.

I am trying to use ADS131A04.

The prototype board (manual wiring) was able to get data without problems.

The variation in the acquired data was judged to be excellent because it was within 20 counts.

So I made a printed circuit board.

Unfortunately, there were fluctuations of up to 1000 counts or more in the acquired data under certain conditions.

That is, when the voltage applied to AVDD is changed, the acquired data varies in the voltage range around 4.9V.

Even when the prototype A / D is connected in parallel and operated simultaneously,

The problem does not occur in the prototype A / D, but only in the A / D on the substrate side.

(If the prototype A / D is connected in parallel, the variation will be smaller and the voltage range will change slightly.)

Therefore, it is not a problem such as oscillation in the analog part,

I think there is a problem with A / D.

The graph below shows the A / D value while lowering the AVDD voltage manually.

(A / D on printed circuit board and A / D on prototype board.)

It can be seen that the problem occurred when the AVDD voltage was around 4.9V.

There are minor symptoms at other voltages such as around 4.7V.

The power supply voltage and the reference voltage were also examined by simultaneous capture, but no fluctuations that could be causal were found.

I was worried about mistakes in digital data, and I added a CRC.

There was no CRC error.

 

Is there a problem with routing the printed circuit board pattern? I think, but I would appreciate any advice.

 

  • 0
    TI__Guru* 97425 points

    Hi,


    Just to be sure that I understand, you've built two systems with these device (one prototype and one PCB) and you're making measurements. When you vary the power supply (and it appears that you are varying it from 5.1V to 4.5V, you see prototype making consistent measurements (with maybe some amount of change due to PSRR). With the new PCB, you see some larger changes in the measurement. One where the supply drops below 5V and another smaller one where the supply voltage drops below ~4.74V and maybe another when the supply drops below 4.64V.

    I don't know of anything that would cause something like this. However, I'm sure there are possible system issues that could show up as something similar.

    Can you provide a schematic for your system? I'd like to know about all of your connections to the device and what settings are being used. I'd like to know about the prototype and the new PCB. What are you measuring and how is that powered up?

    Have you tried taking a series of measurements when the supply is 5.1V and then another series of measurements when the supply is 5.0V (or 4.74V) to see if there is any kind of time variation in the measurement (to see if there's any oscillation or periodic error in the measurement)?

    I know this is quite a bit, but I'll need more information to help debug this problem.


    Joseph Wu

  • 0 in reply to Joseph Wu
    Prodigy 30 points

    Diear. Joseph Wu
    Hello.
    Thank you for your quick response.
    It takes time to make the circuit diagram public.
    I'm sorry, please wait.

    The current measurement data is obtained by simultaneously acquiring two A / D (product, prototype) data with one microcomputer and outputting them to a personal computer through serial conversion. Averaged to 20sps.
    The front-stage differential amplifier output is connected in parallel to two A / Ds(product, prototype).
    When connected in parallel, the problem symptom changes greatly (the fluctuation value becomes smaller and the voltage range moves), so the connection to the prototype A / D has a 10kOhm resistor in series to reduce the change in conditions.
    The Ch.1 compares zero input simultaneously as comparison data.
    AVdd is supplied from an external power supply for experiments, and AVdd (9 pins of product A / D) is measured with Ch.2 (display value is calculated and displayed from prototype A / D data).
    This is a continuous measurement while lowering the voltage manually.
    I think that the small change of AVdd is due to the change of current consumption (LED blinking for operation check), but I don't think there is any voltage drop to 4.7V.
    Next time, stop blinking the LED and try to collect data.
    I think that there are no time fluctuation, temperature change, vibration, periodicity, etc. in tens of tests.
    Prepare a circuit diagram.
    My best wishes.

  • 0 in reply to user6205274
    TI__Guru* 97425 points

    Hi,

    I haven't heard from you for a while so I thought I'd check on you problem with the ADS131A04. If you're still having problems with this device,  I'd like to see a schematic for your application (as I mentioned in the last post). I'd also like to see a better description of the problem that you're having. I'm a bit confused to about what connections that you have to the device and what changes you are making to see the changes in data.

    I'll still close this thread for now, but if you are still having problems with this device, post back and we'll continue to work on this problem.

    Joseph Wu

  • 0 in reply to Joseph Wu
    Prodigy 30 points

    I'm sorry.

    I was late because I did not get permission to publish the schematic.

    In the meantime, review the data sheet,

    1. Do not attach an inductor to the power line.

    And FBn was short-circuited.

    2. The 14th terminal (RefExt) is an input terminal, and the output terminal is a 12th terminal.

    I found and corrected the circuit.

    Furthermore, in order to reduce the influence of connection, it changed to the connection from a prototype board.

    A circuit diagram with these modifications is shown below.

     

    Even after these corrections have been made, the symptoms are similar. Below.

     

    Last time, I wrote that there was no influence of temperature etc.,

    This time, when taking data immediately after turning on the power from the cold state, the abnormal voltage range and the symptom with different data fluctuation were obtained as follows.

    The above data is taken after leaving the power on for about 2 hours.

     

    The prototype circuit is shown below.

     

    In any case, there is a problem with A / D on the PCB, and there is no problem with A / D on the prototype board (manual wiring).

    Do you have any advice?

  • 0 in reply to user6205274
    TI__Guru* 97425 points

    Hi,


    I just noticed that this post was unresolved. I'm sorry that I missed this. Out of curiosity, have you been able to solve the issue that you find on the PCB and not on the prototype board? As I mentioned in previous posts, I need more detail about the issue that you are seeing. Does the output data have unusual characteristics when the AVDD is at the points where there is change in the input voltage. Does it have different amounts of noise or is there a periodic signal on it. Additionally, does the reference change significantly at these points as well.

    If you are having problems, post back and we can continue working on this.

    Joseph Wu