I am looking at using a SOM1 module in a design, but after investigating the schematics for a while I get the feeling that this module is not very well designed (or documented)
Has anyone noticed the connection from PIOBU0 <-> MIC2800-LOWQ? Atmel forgot to mention it in the,... erm "documentation".
If LOWQ is pulled low, LDO1 and LDO2 have a maximum output of 10ma according to the datasheet. -
"LOWQ mode also limits the output of both LDO1 and LDO2 to 10ma"
If you have a system with **VDDBU connected to a battery**, I can imagine :
1. Firmware goes into a low power state.
2. Firmware sets PIOBU0 = low (LOWQ mode). 10ma max on LDO1&2
3. System reset occurs for some reason (low power or FW bug)
4. System is now bricked. LOWQ is still low after reset, and the CPU cannot boot on only 10ma VDDCORE.
5. The only way to recover is to remove all power (including battery)
Am I missing something or am I just stupid?
Of course it's also possible that the MIC2800 datasheet is wrong. They are both Atmel/Microchip so that's a definite possibility.
I'm also not convinced that the SOM1 respects the power-off sequence requirements regarding VDDFUSE. And why is VDDFUSE permanently powered anyway??? At least that is fixed on the (new) WLSOM1 module...