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CD4051B: problem on using cd4051 chip

ming li50749
Intellectual 430 points
Part Number: CD4051B
Other Parts Discussed in Thread: ADS1259, OP07

Hello, TI


Recently we used ads1259 and cd4051 multiplexers for adc data sampling, and found a very strange problem in the development process.

 

ads1259 works on pulse control mode and read data operation in stop continuous mode.


There are 9 sampling temperature sensors and 6 pressure sensors on our external circuit. The pressure sensor uses 4-20ma sensor for sampling. The schematic diagram is as follows:

When I plug in the 4-20ma sensor (pressure sensor) on the p1 port, and the p2 and p3 ports are open, the correct voltage value of P1 can be measured, but the voltage value of p2 differs greatly from the actual voltage value. The voltage value of p3 is similar to the actual value. In theory, the values ​​of p2 and p3 should be about the same size.
I suspect that cd4051 introduces related noise and crosstalk. My test flow is like this. First, open the p1 channel, ads1259 starts sampling, then immediately switches to p2 channel, then waits for 500ms, ads1259 continues sampling, but the value of p2 channel is incorrect, continue to switch to P3 channel, wait for 500ms, ads1259 continues sampling, the value of p3 channel sampling is correct.


I tried other channels, for example, using p4, p5, p6, p4 with sensors, p5 and p6 open, P5 data is error, p6 data is correct.


Does cd4051 have any problems?


Looking forward to your reply!
Thank you!

  • 0
    TI__Genius 9132 points

    Hi Ming,

    • Does port 1 mean channel in/out 1 of the CD4051?
    • There are no known issues with the CD4051. You could try removing the CD4051 and testing without the mux to see the system impact.
    • The two decoupling capacitors are good (one for VDD and one for VSS) however, since you  have multiple CD4051’s – you should have decoupling for each device.

    Thanks

    Saminah

  • 0 in reply to Saminah C
    Intellectual 430 points

    Unfortunately, I did not express it clearly.


    P1 is the connection to the 4-20ma sensor, the differential input of the op07 amplifier, not channel 1 of the cd4051.
    I have already shown it in the picture.


    I can confirm that the ads1259 sampling function is correct.

    However, when the cd4051 switches to p2 port from the p1 port, if the P1 has a 4-20ma sensor inserted and the p2 port is open (ie, no 4-20ms sensor is inserted), the sampling of the p2 port will be problematic，The actual voltage value (use High precision multimeter measures is -0.004)is greatly diff from  the sampled value(+0.0003).  then i switch to p3 port is open (also no 4-20ma sensor) from p2,the p3 value is correct. This phenomenon is very strange。

    why does it happened?
    Thank you!

  • 0 in reply to Saminah C
    Intellectual 430 points

    i have decoupling for each device.

  • 0 in reply to ming li50749
    TI__Genius 9132 points

    Hi Ming,

    Can you use replace the cd4051 with a new one and check if you get the same output ?

    If you still see the same issue, let's try running the tests by first removing the ads1259 and then the mux.

    Thank you,

    Saminah