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Question about CN0359 (ADC, signal line connection)

Pins 38 and 40 of ADUCM360 shown in the reference circuit diagram of CN0359 are connected to the "AD8253_A0" signal.

   1) I would like to ask what is the meaning of connecting pins 38 and 40 of ADUCM360 in the above "AD8253_A0" signal.

 

   2) I don't use ADUCM360, I want to use a different processor. The processor I'm going to use doesn't have a 24bit ADC.

       Please recommend your company's ADC that can be used as an external ADC (using I2C communication) that can be used instead of the ADC inside the ADUCM360.

We ask for your help.



modify to I2C interface (Ext ADC)
[edited by: Justin.Jung at 6:52 AM (GMT -5) on 14 Jan 2022]
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  • Hi Justin,

    1. Pin 40 is the GPIO used to for A0 value of the AD8253 gain selection. Pin 38 is used as PWMSYNC. The PWMSYNC works as a reset for all PWM counters whenever a transition occurs on the pin. Here is a snippet of the line of code in pwm_open() function in pwm.cpp. This configures the pin for PWMSYNC function

    Here is a snip of the ADuCM360 Hardware User Guide for the PWM synchronization feature:

    2. For the ADC, I'll recommend the AD7124-8 which is also a 24-Bit Sigma-Delta ADC (AD7124-8 Datasheet and Product Info | Analog Devices). It has been used in several projects and also in a water conductivity/TDS measurement board (CN0411 Circuit Note | Analog Devices)

    Best Regards,

    Nikko

  • I have an additional question to ask in addition to your answer.

    1) Why use PWMSYNC?
    2) My CPU doesn't have PWMSYNC function, so if I don't use this function, will there be any problem in measuring the conductivity?

    Thank you rogueC for your support.

  • Hi Justin,

    Sorry for the late reply. I missed your additional question.

    1. The CN0359 continually does sample-and-hold of the positive and negative voltage and current through the conductivity probe. When the gain is changed, it is possible that one or more of the 4 measured values were taken from the previous gain setting which will mess up the computed conductivity value at that point. PWMSYNC ensures that this does not happen.

    2. An alternative to this would be to disregard or even stop sampling when changing gain and restart the pwm signals once finished.

    Best Regards,

    Nikko

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  • Hi Justin,

    Sorry for the late reply. I missed your additional question.

    1. The CN0359 continually does sample-and-hold of the positive and negative voltage and current through the conductivity probe. When the gain is changed, it is possible that one or more of the 4 measured values were taken from the previous gain setting which will mess up the computed conductivity value at that point. PWMSYNC ensures that this does not happen.

    2. An alternative to this would be to disregard or even stop sampling when changing gain and restart the pwm signals once finished.

    Best Regards,

    Nikko

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