ADAU1701 - Writeback duration is indeed 73usec?

Hello all,

Looking at the ADAU1701 datasheet, page 28 under writeback section, I understand that I need to keep the power supply "alive" for 73usec in order to complete a safe writeback:

"The maximum number of bytes that is written back from the ADAU1701 is 35 (eight 4-byte interface registers plus three bytes of EEPROM-addressing overhead). With SCL running at 384 kHz, the writeback operation takes approximately 73 μs to complete after being triggered. Ensure that sufficient power is available to the system to allow enough time for a writeback to complete, especially if the WB signal is triggered from a falling power supply voltage."

But If I do the calculation, I think there is a mistake

If the SCL frequency is 384KHz, so one bit duration is 1/384,000 =  2.604usec

So, 35 bytes takes 35*8*2.604usec to write, and this is equal to 730usec, and not 73usec as mentioned.

I wanted to check the writeback procedure duration using the EVAL-ADAU1701MINIZ (after modifying the writeback transistor trigger so that it will actually work...)

I probed the EEPROM SCL pin, while disconnecting the main power supply:

I could clearly see that the writeback duration is about 824usec, that is more closer to 730usec than 73usec...

Is this correct?



[edited by: Nir76 at 11:26 PM (GMT 0) on 7 May 2020]
  • I was just reading the application note AN-923 (Designing a System Using the ADAU1701/ADAU1702 in Self-Boot Mode) and noticed that the wrtiteback duration was fixed:

    Why there is no revision update in the ADAU1901 datasheet? one can easily make a mistake and not adding enough capacitance to keep the power supply active long enough...


  • +1
    •  Analog Employees 
    on May 12, 2020 11:00 PM in reply to Nir76

    Hello Nir,

    This certainly looks like a calculation error. This is an old datasheet so that makes it difficult to change but it is not an automotive part so that helps. This is not a change in the specifications in any way, it is just a typo in the descriptions so I think I can change this without creating lots of paperwork. 

    Dave T