I looked for the power required by the System on Module (SoM) we are going to use (MCV-6DB). We are using the LVCMOS 3.3V standard, so every FPGA bank will be supplied 3.3V. According to the Wikipedia page of another SoM manufacturer, the maximal power consumption is 8.5W for a very similar FPGA (5CSXFC6) to the one we will be using (5CSEBA6). With a supply of 3,3V, we then have 2.58A. This result doesn’t include the power consumption of the peripherals included in the SoM. With the Power Calculator provided by Micron, and using the DDR3 datasheet (K4B4G1646D), I find that a single module of 4Gb will not exceed 300mW. So 600mW for the two of them. The eMMC (MTFC4GLDDQ-4M IT) has a typical current consumption of 70mA when active, according to Micron documents (link).
Compared to our last posts, we have updated our architecture. We realized that the only SDIO capable bank off the FPGA was used internally on the SoM to connect the HPS to the eMMC. This means that we can’t use SDIO to communicate with an SD card at high speeds. Fortunately, we won’t need high speeds from the SD card since we will be able to take our time at the start of the system in order to transfer the data to the much faster eMMC or DDR. So we will connect the SD card to the HPS through SPI.
We wanted to supply the mobile part with 5V which could then be directly used by some of the components (LED and synchronization mechanism for example), and converted to 3.3V for the rest of them (SoM, LED driver, …). However, it appears that the voltage will be subject to instabilities because of the way the power is transmitted through the rotating part. We have to account for that by using large capacitors as well as a higher supply voltage: at least 12V. So we will have to convert 12V to 5V and 3.3V. We are not sure if the conversions 12V->5V and 12V->3.3V are better than 12V->5V->3.3V. In the latter case we would use the component we originally considered : PTH05060W from TI (under review by Alexis).