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Digital & Analog connect

Category: Hardware
Product Number: ADAU1701

Hello, I am working on a circuit with ADAU1701 and I am having some issues with the analog input. Specifically, when I connect to the BTM334 module, I completely removed the crystal oscillator to supply MCK directly from BTM to ADAU. I have heard that without the crystal oscillator, the ADC of ADAU cannot run. Is there any solution that would allow me to get both analog and digital signals without having to add any components? Thank you.

  • Hello Stevie,

    You must feed the ADAu1701 with a master clock that comes from the Bluetooth module. If the frequency of the incoming bit clock and sample rate clocks on the serial port does not divide evenly into the master clock that is coming into the 1701, then the internal digital flags it as an error and mutes the audio. 

    This is a problem with most Bluetooth parts. I do not think it will have a high master clock output? It needs to be a multiple that the PLL can lock to. This is detailed in the PLL section of the datasheet. You have to set the PLL-Mode pins correctly. See table 12 in the datasheet. There is a setting for 64x fs which an I2S bitclock output will be. So you may be able to use that if you can change the settings on the pins. It is not easy on our small eval boards and other aftermarket ones also do not make it easy. Although, that said, both pins need to be low. As long as there is a pull up resistor you may be able to just ground them. It will waste some power but it will work. Obviously you cannot do that if the pin is directly tied high. Unless you like letting the magic smoke get out of the regulator on the board. 

    The other thing to note here is that the part will not boot up or function until the Bluetooth module starts sending clocks. If nothing is paired with it there is a chance it will output nothing so nothing on the DSP will work. 

    The ADAU1452 is the better part for dealing with Bluetooth because it has a sample rate converter that the Bluetooth can use. Then you do not need to synchronize to it. the ASRC will do that for you. The DSP can operate in its own clock island. 

    Dave T

  • In Vietnam, we don’t have any e-commerce platforms selling the ADAU1452 learning module, and the datasheet doesn’t include a sample schematic. Could you provide me with a sample schematic for reference? I really like it, but purchasing from international e-commerce platforms takes a long time, and I don’t feel confident about it.

  • Hello Stevie,

    I do not have a schematic for a design that is using a Bluetooth module. However, we do have the schematic to the eval board in the user guide. 

    EVAL-ADAU1452RevBZ Evaluation Board | Analog Devices

    You can bring in a Bluetooth evaluation board I2S signal into the headers for the serial input ports 2 or 3 on this eval board. So it will be easy to prototype and interface. 

    I can provide you with a starter project for the SigmaStudio schematic if you need that. 

    You will need to route the Bluetooth input to the ASRC then into the DSP core. 

    Dave T