PCM1860: Using multiple I2S sources and switching between them

Hossam Moghrabi

Part Number: PCM1860
Other Parts Discussed in Thread: PCM1864, , TMUX1309, PCM1862

Hello,

I have a project which has multiple audio sources, all I2S signals.

I decided to use PCM1860 since it is significantly cheaper, but the question stands for PCM1864 as well.

I don't know about master or slave to be honest. However, here are the audio sources that I have:

1- Source 1: I have 3 analog audio inputs, all go to PCM IC and it outputs I2S signals DOUT, BCLK, LRCLK.

2- Source 2: I also have another IC which takes HDMI video and delivers parallel video bits (60 bits) + audio as I2S output.

3- Source 3: external I2S input from a PCM1860 which is outside the device itself. So the device will have only the 3 I2S signals.

4- Source 4: same as source 3.

All of them will go to 2 HDMI transmitter ICs which has up to 6 I2S inputs. However, the HDMI IC has one BCLK and one LRCLK inputs, but has 6 DOUT inputs. Therefore, I need to route all 3 signals from each source when I choose it. I thought of why not just use one BCLK and one LRCLK from one of the sources for all sources and just route the DOUT... will it work? I figured this since they are just clock and word select.... all sources are 192khz too.

Another solution If this won't work is gettingTMUX1309 to switch all 3 signals for all 4 sources... all TMUX1309 ICs take inputs without buffering. please check the attached image for schematic.

please check and get back to me if this works.

Here is the attached image: https://imgur.com/a/aCBsuRq

best regards

over 2 years ago

0 Sanjay Dixit over 2 years ago

TI__Mastermind 23030 points

The Data DOUT From Each source is in sync with its own BCK and LRCK. Therefore you cannot use 1 of the BCK and LRCK for all sources.

Only condition this was possible if all the i2c generators had a common Master Clock

0 Hossam Moghrabi over 2 years ago in reply to Sanjay Dixit

Prodigy 190 points

Ok, I understood.

So is my TMUX1309 solution good? I mean for switching them all.

0 Sanjay Dixit over 2 years ago in reply to Hossam Moghrabi

TI__Mastermind 23030 points

Yes you can try this. But at any time only the 1 selected I2S channel shall go to HMI Transmitter

0 Hossam Moghrabi over 2 years ago in reply to Sanjay Dixit

Prodigy 190 points

so TMUX1309 concept works perfectly right? of course, I will feed only one source at a time meaning DOUT + BCK + RLCLK for one source at a time. but will this analog switch cause any delay or so? this is important.

on a side note, how should I connect PCM1860 master or slave and what is the main difference? I only need to switch between 3 analog audio sources, no extra option needed. I don't have an external clock signal or anything, I need pcm1860 to do its job by itself without extra crystal or anything. kindly help me.

thanks

0 Sanjay Dixit over 2 years ago in reply to Hossam Moghrabi

TI__Mastermind 23030 points

The simplest way to operate the PCM 1860 is Master mode where you just connect a crystal to the chip and the chip makes BCK,LRCK and Data. A few hardware control signals can be used to set it up.

Slave mode would mean you externally generate a external SCK. This is a ask by itself

The TMUX1309 Has a RDS on OF 350 ohms.. If you choose a Fs=48Khz B=48K*64=3.07Mhz OR ts=0.32us.

Generally the out put of the TMUX device would drive a 10pf load of the input pin of an IC. The 350 ohm and 10pf make a low pass filter with a time constant of 22ns which is much smaller the 0.32 us so it should work.

I would say you could think to look at devices with RDS on in the 100 ohm region and this would be even better

0 Hossam Moghrabi over 2 years ago in reply to Sanjay Dixit

Prodigy 190 points

Ok then I will get a crystal, should it be 27 mhz or what exactly?

TMUX1309 is the cheapest and most suitable, do you have a better alternative? it is listed as 59 ohms RDon on your parametric website but 350 ohms at 3.3v in datasheet. closest I could find is SN74LV4052APWR but I still need to be sure it is directly compatible. it lists in datasheet a typical resistance of 34 ohms and terminal capacitance 13.1 pf. what do you think?

I still need to know how to set up this FS=48khz*64 setting, so for your kind help. Kindly mention all hardware settings I need to put then which pins I need to change when I want to change the input source. Therefore I should have constant hardware settings and variable ones.

0 Sanjay Dixit over 2 years ago in reply to Hossam Moghrabi

TI__Mastermind 23030 points

In PCM1860 The hardware Master mode is set up by putting a Crystal between Pins X0 and X1. The device shall output BCK and LRCK as well as DOUT for I2S Mode.

The Ratio of BCK/LRCK is internally set up as 64 in the device.

pin description:

MD4=Low For I2S

MD1,MD0 =High,High 256*fs master mode

MD6,MD5,MD2 shall select the audio source as in table above.

For 48K at 256*Fs choose a 12.288Mhz Crystal.

BCK output shall be 48k*64 OR 3.072Mhz

LRCK shall be 48Khz

DOUT shall be 32 Bit audio

0 Hossam Moghrabi over 2 years ago in reply to Sanjay Dixit

Prodigy 190 points

Hello,

I want it to be of equal performance to PCM1862. I mean, all transmitter IC and designs I saw uses 192khz sampling rate, is there a way I can use it here and how?

why choosing 256*fs? can you kindly explain the options?

I saw that to get 192khz I should have a crystal of 49.152 mhz, so I got this one: https://www.digikey.com/en/products/detail/kyocera-international-inc-electronic-components/CX3225GB49152P0HPQCC/4896400

will it work?

if so, please list the hardware configuration I need to do so I can refer to them.

0 Sanjay Dixit over 2 years ago in reply to Hossam Moghrabi

TI__Mastermind 23030 points

Yes you need a input frequency of 49.15Mhz but this cant be done with a Crystal and the on chip oscillator on the chip as the maximum frequency allowable is 35Mhz . You will have to insert a CMOS Clock on SCKI pin in order to do this.

I would suggest to look for Modules that can produce this frequency. Its a package that accepts a Vcc and Gnd and produces a Desired frequency.

The 256*Fs are fixed options that are built into 1860 Hardware version .

0 Hossam Moghrabi over 2 years ago in reply to Sanjay Dixit

Prodigy 190 points

Hello,

you mean oscillators like these:

https://www.digikey.com/en/products/detail/microchip-technology/DSC1001AI1-049-1520/7732560

https://www.digikey.com/en/products/detail/sitime/SIT8008BC-13-33E-49-152000/11412807

ok so besides this oscillator + 256*fs... I only need to set the desired inputs right?

thanks

0 Sanjay Dixit over 2 years ago in reply to Hossam Moghrabi

TI__Mastermind 23030 points

A oscillator of this style can be used. However we need to meet the timing requirements

If we give a suitable MCLK in Master Mode the device shall generate BCLK and LRCK which along with DOUT will be the digital audio,

0 Hossam Moghrabi over 2 years ago in reply to Sanjay Dixit

Prodigy 190 points

hello

the 2 ones I posted are of required 49.152mhz frequency output, so what is wrong with them? or what more requirements I need to take care of?

0 Sanjay Dixit over 2 years ago in reply to Hossam Moghrabi

TI__Mastermind 23030 points

I would think it should be fine, Only thing which may be a concern is that the duty cycle of your part goes from 45% to 55% while our spec is tighter going from 48%-52%.

I would suggest to try it out in a practical setup . You could try testing from 20 deg to 70 deg ambient.

0 Hossam Moghrabi over 2 years ago in reply to Sanjay Dixit

Prodigy 190 points

Hello

I have searched but found all parts in this category in Digikey are 45-55 duty cycle. what could go wrong?

I cannot try in practical setup since the board is far from ready and will be very expensive.

can you suggest a better solution?

on the other hand, for the subject of switching the I2S signals.. how about SN74LV4052APWR, is it better that TMUX1309?

0 Sanjay Dixit over 2 years ago in reply to Hossam Moghrabi

TI__Mastermind 23030 points

The SN74LV4052APWR should be a good choice.

In most probability the crystal Oscillator itself should work well in your application.

Another Thought: It may be an overkill.

If you can get a crystal for 49Mhz*2 and follow it up with a D Flip flop set as a T Flip Flop you could get 49Mhz at exactly 50%.

https://www.ti.com/lit/ds/symlink/sn74lvc1g74.pdf?ts=1636446087880&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FSN74LVC1G74

Tying Q- to D and giving input at CLK should make this work as /2

Audio

Audio forum

PCM1860: Using multiple I2S sources and switching between them