Hello
we try to debug a system with DM6446 DSP. We want to use microSD cards. We also use a Sd card multiplexer to provide other SD communication (in the future we plan to use wifi modules that require sd bus). We have a problem with the signals of the microSD card. In detail, we see that the SD clock generates noise in the signals of the SD card. It seems that the clock is coupled with the signals. In this situation we can't mount correctly the device.
The pcb routes are 2 lenght from DSP to SD mux and 12cm length fron SD mux to microSD connector, 0,16mm wide, 35um thick and 0,3mm spaced. The lines are designed on the same plane of the PCB. The lines are on an internal plane between two power planes (GND and 3.3V). The case of the microSD is not connected to the ground, but even if we connect the case with the ground the clock is coupled with the signals too.
We tried the system without the Sd mux but the problem remains the same. We tryed to lower the pull-up resistances to 1K and it seems that the problem lowers but in this way we use more current and we do not use the suggested pullup configuration of the bus.
Is there anyone that can help us? Could be a supply problem? Are there some constraints about the pcb routing of the SD card signals? thanks for the replies.