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Original question:

TM4C123BH6PGE: Current Loss in TM4C123BH6PGE During One-Wire Protocol Implementation

TM4C123BH6PGE: Power Oscillations During I2C Reads and CAN Messaging

ygt ulk
Prodigy 100 points

Part Number: TM4C123BH6PGE

Hi, I'm using I2C to periodically retrieve data from a peripheral device every 40 ms and then transmit these data via CAN with variable intervals.

For instance, Message 1 is sent approximately every 100 ms, while Message 4 is sent around every 4 ms, among others.

However, I've noticed that when I decrease the periodic message transmission times (e.g., to around 1 ms), i am seeing oscillations in the power supply current .

Has anyone encountered a similar issue before?

  • 0
    TI__Guru**** 191886 points

    Hi, 

      Have you referenced the TM4C123 System Design Guideline? https://www.ti.com/lit/pdf/spma059

      Please ensure you have sufficient decap on the VDD and VDDC power supplies as described in the document. 

  • 0 in reply to Charles Tsai
    Prodigy 100 points

    Hello, the decoupling for VDD and VDDC is adequate for the MCU board, but I suspect the peripherals are causing oscillations in the power supply.
    I have 2 images that show the current (in blue) and the I2C operation (in yellow).
    In Image 1, the periodic CAN messages are disabled.


    Image 1. Current - Blue, I2C -Yellow




    In the image 2 periodic can messages are enabled.

    Image 2. Current - Blue, I2C -Yellow



    As you can see, there is a significant drop in current about 10 ms before the I2C communication starts. Not only that, the communication rate of I2C seems to slow down.

    Based on these images, it appears there is a correlation between the rate of CAN messages sent from my device and the I2C peripheral used for voltage reading.

  • 0 in reply to ygt ulk
    TI__Guru**** 191886 points

    Can you reproduce the issue on a Launchpad?