Writeback trigger circuit on EVAL-ADAU1701 MINIZ board
Hello,
I don't understand the working of the writeback trigger circuit on EVAL-ADAU1701 MINIZ board as explained on page 7 of the documentation file EVAL-ADAU1701MINIZ.pdf
It seems to me that if the two large capacitors are situated on the **input** of the voltage regulator, the base of Q2 will not see a dump until it is too late to do a writeback. I think that C15 and C16 could/should be on the output of the voltage regulator (stability ??) or that there must be an isolation diode between DVDD and the input of the voltage regulator (with a discharging resistor to ground) like on the enclosed sketch.
May be there is error in the schematic of the board shown on page 8 ? And the question is : how works the evaluationboard ?
Kind regards.
Peter Greuter
Audio Signal Processors
SigmaDSP Audio Processors
evaluationboard
adau1701
Peter, your understanding is correct. The EVAL-ADAU1701 MINIZ board is set up in a way such that the writeback trigger will not work. The capacitors would have to be on the other side of the power supply in order to get the proper functionality. This issue is on our list of proposed edits for that evaluation board. However, with resources limited at the moment, this update has taken a low priority relative to other tasks.
On the larger EVAL-ADAU1401EBZ board, we provide a jumper that allows the user to manually toggle the writeback line and trigger a writeback to the EEPROM.
Hello BrettG,
thanks for the fast answer ! Now I am proud that at age 65 I am still able to find errors in modern schematics
Kind regards from sunny Paris/France.
Peter Greuter
Haha, yes it looks like you read the schematic correctly!
Although this feature works and can be tested on the larger evaluation board, I would personally recommend against using it. The whole concept of that feature is to be able to design a system that operates entirely without a microcontroller, by keeping the system memory entirely in the EEPROM. However, something is scary about the idea of doing a last-second write to EEPROM after the power plug has been pulled. If anything goes wrong, for example - if the power supply browns out during the write, then the date will be corrupted. Unfortunately, without a microcontroller, there's nothing you can really do to correct that error afterwards. So, I'd avoid using that feature and instead try to use switches or potentiometers for any value that you want to save between resets.
Greetings from rainy/cold Boston.
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