I looked through the datasheets and App notes and couldn't really find a straight answer, so here goes.
I have a design which incorporates an atTiny2313A, operating at roughly 5.5V nominal. The device contains 32 bytes of SRAM, which upon some signal I wish to backup any changes to the EEPROM. The catch is, the signal will come shortly before I lose power. How much time I have will depend on how long a fully charged capacitor can retain voltage.
So the questions are as follows:
1) How much time do I need? The datasheet claims that an erase/write cycle takes 3.4 ms. However, elsewhere in the documentation there is a discussion of a "page" consisting of 4 bytes. This implies that perhaps only 8 writes are necessary to backup the data. But I'm not clear that this isn't an external programming mode that doesn't apply to EEPROM writes from within the code.
2) What is the minimum voltage required to safely write to the EEPROM? Based on looking at the datasheet I'd say 2.7V, but it doesn't explicitly say that.
3) Assuming I am running on the 8MHz internal oscillator, and doing nothing other than writing data, what is the minimum current consumption I can expect to achieve? Is there a particular technique to do so.
I'm figuring the capacitance I need will be I(min) * time (required to write) / (5.5-V(min), plus some safety margin.