PCM1789: Audio forum

Ilia Hadzhiev

Part Number: PCM1789
Other Parts Discussed in Thread: DIR9001,

Hello,

I cant get any audio signals on the output of the IC. I am attaching the schematic circuit. The input I am using is from PC/SPDIF. Every thing seems fine with DIR9001:

Measured:

LRSCK: 48 kHz
BCK: 3 MHz

Din: changing with the SPDIF input
SCKO: 12.288 MHz

I think I have config PCM1789 correctly for HW mode.

6646.Doc1.docx

over 3 years ago

0 Ilia Hadzhiev over 3 years ago

Prodigy 200 points

I just put pull up resistor to AMUTEI and I have output now, but it is now what I expected. The signal is not changing its amplitude, only frequency Doc1 - Copy.docx

+1 Paul_Frost over 3 years ago in reply to Ilia Hadzhiev

TI__Guru 52663 points

Hi Ilia,

From my initial inspection it looks like your I2S formats are not correct. You PCM1789 is configured for left-justified I2S but your DIR is configured for standard I2S. This results in the most significant bit being ignored, so you would see something like your output. I recommend you connect the FMT pin on the PCM1789 to GND.

PCM1789:

DIR9001:

Thanks,

Paul

0 Ilia Hadzhiev over 3 years ago in reply to Paul_Frost

Prodigy 200 points

Hi,

after I changed it the output at maximum volume is with amplitude 2.6V and is DC biased 1.75V ( 0.85 V p-p )

0 Ilia Hadzhiev over 3 years ago in reply to Paul_Frost

Prodigy 200 points

https://docs.google.com/document/d/1T4dAWpXyppY4j7c9V-v0ZDy22NFYxuAZKON09Rpbg8c/edit

this is link with the oscillogram, this time I can change the amplitude, but I expected 4V pp

+1 Paul_Frost over 3 years ago in reply to Ilia Hadzhiev

TI__Guru 52663 points

That DC bias is low, can you confirm the VCC voltage and the output voltage on the COM pin? In addition, your schematic does not show the output circuitry - do you have any amplification?

How confident are you that you are providing a 0dBFS input to your device? If you have a PC generating the SPDIF input, you might have some other software attenuation. You might try an instrument source for the SPDIF to confirm.

0 Ilia Hadzhiev over 3 years ago in reply to Paul_Frost

Prodigy 200 points

VCC - 5V
VCOM - 2.5V
VL - to GND 2.5V

VL- to VL+ differential 2.2V DC

this is measuered before amplification