Hello,
I'm a little unclear as to where to post this exactly, but since we are using a C2000 in this application, I will post here. If anyone knows of a better place for me to ask this question, I would be happy to transfer to the proper forum.
We are designing a professional home audio system, and are using a TMS320F28027 to control an LCD display as well as send commands to a DSP on the main board. The commands to the DSP are being sent by I2C. What is happening is that the I2C is generating a LOT of noise whenever it communicates. We have managed to track it down with a scope. On every falling edge of the SCL or SDA lines, a very narrow negative spike is created. The magnitude of the spike is in the neighborhood of 1 volt or so. It's very narrow, 20 or 30 ns or so, but it is causing some rather significant noise in the analog ground bus as well, which is being produced as noise in the speakers which is very noticeable when the input signal is nil.
We are using 2.2k pull up resistors. We have tried adjusting the clock from 100khz to 400khz and even 1mhz, and this does not appear to make any difference. We have experimented with putting caps on the I2C line to filter and even diodes. Nothing appears to make much difference up to this point. The diodes do prevent the negative spike, but they also kill the signal and make it useless.
Has anyone dealt with this kind of issue before, so that they would have any suggestions?
Thank you in advance.