Zym Dap

STM32L053C8 I2C PullUp Problems

Discussion created by Zym Dap on Apr 5, 2018
Latest reply on Apr 5, 2018 by AvaTar

Hello,

 

I've been using STM32L053C8 uC for my project. I need I2C interface to communicate with MCP9800 thermometer. There are no more ICs connected to this I2C bus on my board. There are no external pull up resistors as I'm using internal pullups (settings configured via CubeMX). At first, it worked, then started to crashing and stopped reading the temperature. Debbuged with an oscilloscope. What I found out is that, after connecting power supply, SCLK and SDA levels are high as they should be (2.7V my power supply voltage). After working a few minutes levels randomly drops and huge noise appears, levels jumps. Removed MCP9800 thermometer from board - nothing changed. Did something happen with uC? Maybe internal pullups? Is it possible to "save" interface by adding external pullups then?

 

Maybe someone has any idea. I enclose images: "normal" - when uC booted. "After" - when beeing idle 5-10 minutes. Thanks in advance!

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