03-06-2018 09:18 PM
03-06-2018 10:48 PM - edited 03-06-2018 11:00 PM
Depending on how often it is powered up (or, more importantly, how long it isn't powered up), you may have a choice between:
I've had success with lithium thionyl chloride primary cells (~ 3.6V) followed by a micropower LDO, which was handy for me as I also need 3.3Vish for a real time clock on some products.
Given a large enough cell capacity, you'll find that the lifetime is determined more by the temperature than by the (tiny) current for most cell chemistries. Finding reliable information about extended lifetimes as a function of temperature in the datasheet is probably the hardest part of the design process.
EDIT: also read this thread
and this sci.electronics.design thread
03-07-2018 08:27 AM
Thanks for the reply and valuable input. I do already have a Li coin cell for an RTC but was trying to avoid a micropower regulator to reduce voltage to <1.8V so i was wondering of a 1.5V primary cell was an option. I agree that the self-discharge rate is probably the most effected by temp.
However, I am not familiar with effuses. Can effuses be used to permanently store the FPGA decryption keys nd remove the need for a backup battery? I guess I need to look into this more. I will look at the Zynq TRM and data sheet. Any other info about effuses is welcome.
03-07-2018 04:38 PM
UG470 is the document to read for information about efuses in 7 series.
Remember these are OTP - you can only blow a fuse once. Be prepared to permanently brick a board or two while you are experimenting.