I am trying to design a very minimal expansion board for Intel Joule 570x. I appreciate all the amazing documentations (even exp. board design) you provide. They are amazing. I would like to clarify a few points. I will mark my questions with "Q".
My aim is to fit the Joule in a very small space. So, my desired expansion board size is as big as the module itself (populating only the bottom side). I need only a USB 2.0 for my application. I also have the official expansion board, so I am not concerned about dnx, hdmi, usb3(c), rtc, sd card, mipi, eeprom, etc. and removing them all. I am keeping only the uart to usb interface (for debugging). I need drastic changes in the expansion board design. I will use it for research, so, I need the design to be as simple as possible to reduce the prototyping cost (trying to avoid 8 layer board design, if possible 2 layer only). I will share the design with the community as soon as it works.
According to my initial tests, the actual power consumption of the module is relatively low (12V 200mA+ depending on the load). In my system, I have 5V 3.5A regulator. I would like to use that 5V as the main power source of my module (VDC_IN and VSYS). Hence removing the VSYS regulator (BQ25892RTWT) and 5V boost regulator!
Q1. I understand that 5V will be fine (not too much) for VSYS. In the "Joule datasheet, table 6" there was even a suggestion to use 5V for VSYS when using CSI cameras (ok, not my case, but a strong indication that VSYS can be 5V). Could anyone confirm it? Is there any side effect of using 5V VSYS instead of 4.2V?
Q2. Does the computing module really need 5A (rating of BQ25892RTWT) for VSYS? At least my tests were very promising in the average power consumption. I feel like 5V 3.5A (or slightly less) (even 2A) would be enough for VSYS. Am I missing a very important fact that all expansion board designers know by heart? I am aware that datasheet suggest 4A. But, does anyone have any experience? I will not charge a battery or I will not connect any power demanding peripherals. Purely for computation.
Q3. If I remove BQ25892RTWT, I2C_0 will not be used for any other device (I am removing also the eeprom). I will simply leave I2C_0 pins floating. Does I2C_0 have any crucial effect on the booting of 570x?
Q4. I am removing 1.8V and 3.3V regulators. I will use VDD1 and VDD3 (only for 1 level shift chip). Does using 5V for VDC_IN and VSYS affect VDD1 and VDD3?
Q5. To keep the 570x work as it works on the official exp. board (default configuration), (I need only confirmation for following cases)
(a) Leaving hardware strap pins floating is enough. They are already floating in the default design
(b) I do not need dnx. So, leaving UART_2_TXD pin floating is enough.
I would appreciate any answers and suggestions. I am sorry for the very long message. I will answer any questions you may have.