ADAU1761 Self Boot-up Mode

Hello Mezza,

Indeed, the ADAU1761 cannot self-boot, whereas the ADAU1701 can. It's important to note that the ADAU1701 self-boots by reading an external EEPROM - in other words, the memory is still not contained internally. That means there will be a slightly larger amount of board space required for this solution.

The ADAU1701 and ADAU1761 are not exactly drop-in-replacements for each other. They have different packages, different analog I/O configurations, and a few different functional blocks. You might want to read the ADAU1701's datasheet, or at least the first few pages, before making your decision.

If you decide to switch to the ADAU1701, you can learn how to easily self-boot the system here:

Updated self-boot EEPROM image generation / download

You can also learn how to use GPIOs to control the signal flow here:

https://www.analog.com/static/imported-files/application_notes/AN-951.pdf

If you want to stick with the ADAU1761, then you'll need a small microcontroller to boot the system. That requires a bit more work, but luckily we have some tutorials that will get you most of the way there. Here's an example system that uses an ARM Cortex M3 to boot the ADAU1761. It includes full schematics, tutorials, and example code: https://ez.analog.com/docs/DOC-1806

Hi Brett

Thanks for responding so quick. I will have a look into the ADAU1701 and see if it meets our requirements, I am sure it will as our requirement is not very demanding, we are using it to amplify electret microphones and process the audio to help prevent feedback using notch filters. I was getting used to all the registers and filters and getting good results when this issue with self-booting came up.

Thanks again for your help

Mezza

The ADAU1761 has some nice preamps on the front end that were designed to interface with microphones, whereas the ADAU1701 unfortunately does not... but you could remedy that with a simple op-amp preamp circuit on the front end.

That's probably worth the trouble when compared to adding a microcontroller to the BOM.

Hi Brett

I have nearly finished getting a prototype circuit design ready and just have another few questions to ask.

I want to use the ADAU1702 in self boot mode and need advice on how to connect the pin 5 RESET and pin 20 WB.

I envisage the product to have a program downloaded to it via the usb serial connection module onto the ADAU1702. The product will then have to be tuned up, still connected to Sigma Studio and when tuning is completed the serial connection to the pc is removed. On power down of the product all volume settings will be written to EEPROM. On power up of the product all settings stored in EEPROM will automatically be loaded.

now reading the Self-booting application notes it says that self boot is triggered on a low to high signal on reset when selfboot and WP are high. Could this reset pin be tied to the 3.3 supply via a pull up resistor with the provision for a reset switch to ground for reset function. Would a small delay 50ms be required on this pin to allow the chip to power up first before asking for a self boot? (rc filter).

writeback function is a low to high pulse on the WB pin 20 when the device is in self boot mode. Does this have to be triggered manually? The reason I ask is that the product will be switched off frequently and ideally everytime the user switches off the product it should automatically store any volume settings.

I hope it is clear what I am trying to achieve!

Thanks Mezza

Hi Mezza,

For the RESET pin, you should be able to simply tie it to the supply just like SELFBOOT and WP. Even if they all come up at the same time, a self-boot sequence should initiate.

First, please take a look at my FAQ about using the interface registers and doing a write-back on the hardware: https://ez.analog.com/message/48651#48651

This, combined with the selfboot application note you referenced, should get you started.

Now, about the WB pin, the answer is yes... you need to trigger that manually.There are a few ways that you could do that:

Maybe you could have some kind of counter or pulse generator inside the SigmaDSP that would trigger a high pulse on an output GPIO every 500 ms or so. Then you could connect that GPIO pin directly to the WB pin, which would effectively trigger a writeback twice per second. That's an idea I have had, but I haven't tried it before.

You could have the product's on/off switch somehow connect to the WB pin and trigger a writeback, and use an RC or some other kind of delay element to delay the actual powerdown signal that goes to the regulator or power supply. This would give the system enough time to write back before the ADAU1702 or EEPROM lose their power.

You could try putting a massive capacitor local to the ADAU1702 and EEPROM to keep them powered for a short time after the main power supply is removed. You could then use a transistor sensing the main supply line and have that trigger a high signal to the WB pin to initiate the writeback. We actually tried this on our mini evaluation board but it was unsuccessful because the capacitor wasn't large enough, and the writeback couldn't complete in time.

Those are just a few ideas. I hope this is helpful.

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Thank you,
EZ Admin