DAC Question - Microchip RN-52 and Texas Instruments PCM1794A

[dude2k]

Hello everybody,

i'm currently building on a Bluetooth DAC. I hope this is the right forum.

I have a question:
As Bluetooth chip I use the "Microchip RN-52" and as DAC I would like to
use the "Texas Instruments PCM1794A". I would like to connect both via I2S.

Here are the data sheets:
http://ww1.microchip.com/downloads/en/DeviceDoc/70005120A.pdf
https://www.ti.com/lit/ds/symlink/pcm1794a.pdf

The RN-52 has the following pins:
Pin 24 - SD_OUT
Pin 25 - WS
Pin 26 - SCK

The PCM1794A has the following pins:
Pin 4 - LRCK
Pin 5 - DATA
Pin 6 - BCK
Pin 7 - SCK

I'm not quite sure why one has 3 pins and the other 4?
How do I connect them? I think I'm missing something.

Thank you and greetings
dude2k

 

[xx3stksm]

I guess SCK(pin26) of RN-52 means shift clock for SD_OUT(pin24) while SCK of pcm1794A doesn't mean shift clock but system clock. The correct connection is pin26(RN-52) to pin6(pcm1794a). So, what is the counterpart of SCK(pin7) of pcm1794a? Unfortunately, you don't have the right signal from RN-52 like Rpi. Recent interface sometimes fails to have SCK(pin7) because a new DAC chip doesn't always need SCK(pin7).

You have two ways. One is to make SCK(pin7) by a crystal-based PLL. The other is to use a new chip which includes internal PLL like pcm5122. Both are practically possible.

 

[dude2k]

Hello xx3stksm,

sounds reasonable, thank you!
I have have those components and most of the schematic, so I would go for your first solution.

Do you have a recommendation for a crystal-based PLL for me?

Thanks
dude2k

 

[5th element]

Yeah I've used the RN-52 a number of times and it does not output a master/system clock.

You can get around this by using something like an src4192 too between the RN and the pcm1794.

I have also used the RN + one of TI's newer DACs that include an onboard PLL, like xx3 says above and that also works well.

A third option is to use the spdif output of the RN and a spdif receiver. The receiver will then generate all the required clocks you'll need. I did this before the RN had its firmware updated to output I2S.

 

[dude2k]

Hello 5h element,

thank you for your answer.
I think I will give the src4192 solution a try, together with 74HCU04 and a 24.576MHz crystal. Also ordered a PCM5122 for testing.

I'm new to all this stuff, so let's see if I can get it to work.

Regards
dude2k

 

[xx3stksm]

I usually use simple transistor oscillator since it has a wider capture range than hcu04. My phase comparator is done by FPGA. FPGA has internal PLL which also can be used to generate system clock for pcm1794a. But a crystal-based oscillator is a little bit high performance. It's so stable that you can use a simple PLL filter. Capture range with 30pf crystal is about 100ppm(from 24.575MHz to 24.577MHz).

 

[5th element]

Just be careful with the 74HCU04 as that's apparently a logic inverter as well as buffer. Is there some specific reason why you want to invert everything?

The pcm5122 is a nice chip. I've used the PCM5142 and 5242 with their DSPs and they sound great. The datasheets aren't exactly brilliant though when it comes to programming them. That's if you're looking into i2c/spi communication of the 5122.

 

[xx3stksm]

If you want to use TTL for an oscillator, inverting buffer with a single buffer like hcu04(hc04 has double)is necessary. I'm sure non-inverting type like hc386 can't be used.