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TMAG5231: Sensors forum

niyazi özan
Prodigy 10 points
Part Number: TMAG5231

Tool/software:

Hello,

We have a problem about the TMAG5231C1GQDBZR where we use for rain counting with help of magnet mechanism on our devices. The MCU reads all sensors for every five minutes and  device sents datas over GSM to server every one hour. I connect TMAG5231C1GQDBZR output pin to counter IC. The output pins of the counter IC are connected to IO expander IC, so we can read rain count data with I2C. We see that some devices count rain even if they are not exposed to any magnetic field and do not have a magnetic mechanism. When I put 10uF by pass capacitor instead of 100nF (C1) the frequency of rain counting decreases. What is the reason for this problem? What are your recommendations? Could you pease help us about the problem? You can see schematics and PCB layout at below.

Note: There are some traces (I2C signals (SDA snd SCL)) at the bottom of the TMAG5231C1GQDBZR at mid layer as you can see 2D layout.

Best regards!   

           

  • 0
    TI__Mastermind 20950 points

    Niyazi,

    Thank you for reaching out on E2E and welcome to the forum.  This is an interesting design idea.  In this application how are rain events normally triggering the sensor?  Is there some balanced mechanical setup that brings a magnet into proximity of the sensor when a rain event occurs?  

    I did notice that you have a pull up resistor on the output of the device, although this device has push-pull output and this is not necessary.  In the event that the output is driving low, you will draw an extra 10uA current through this resistor.  This is certainly within the output drive strength of the device, however.

    It is interesting that increasing the decoupling is reducing the likelihood of these events.  Perhaps you are getting noise to couple off of the I2C lines that are routed just above the resistor?  I would recommend that you connect a scope to your output and try to set a trigger on your system to capture the state of VCC, Out, and SCL when the event occurs.  This might help give some insight what is happening.

    Thanks,

    Scott