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Adventurer
Adventurer
1,071 Views
Registered: ‎06-30-2013

recommendationfor Zynq 7030 encryption battery

I see the battery requirement for encryption support for the Zynq family is 1.0V to 1.8V at 150nA. Does Xilinx recommend a particular battery? I am looking for a coin cell type but not sure if alkaline or silver oxide is preferred. Would like 10+ year life. Any suggestion are welcome. Thanks, Craig
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4 Replies
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1,056 Views
Registered: ‎01-08-2012

Depending on how often it is powered up (or, more importantly, how long it isn't powered up), you may have a choice between:

  • primary cell (i.e. non-rechargeable)
  • secondary cell (i.e. rechargeable)
  • capacitor (e.g. a double layer type designed for memory backup)

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

 

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1,049 Views
Registered: ‎01-08-2012

Don't forget that you can use efuses, which may remove the need for a backup power source.

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Adventurer
Adventurer
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Registered: ‎06-30-2013

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.

 

Craig

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979 Views
Registered: ‎01-08-2012

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.

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