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SRC4190: Bypass Mode

Sing Lit
Prodigy 85 points
Part Number: SRC4190
Other Parts Discussed in Thread: SRC4192, PCM5142

I'm question about the behavior of SRC4190 Bypass pin.

When I set to Normal Mode (BYPAS = 0), the output sampling freq is 96kHz which it what I expected.

Below is the measurement result (BYPAS = 0)

Input

Output

LRCKI= 44.1kHz

LRCKO= 96kHz

BCKI= 2.822MHz

BCKO= 6.144MHz

 

But when I set to Bypass Mode (BYPAS = 1), I found that the output sampling freq is still 96KHz, I question why the output sampling freq is kept 96kHz? Is it something wrong on the schematic? I expect the LRCKO will be 44.1kHz which is followed with LRCKI. 

Below is the measurement result (BYPAS = 1)

Input

Output

LRCKI= 44.1kHz

LRCKO= 96kHz

BCKI= 2.822MHz

BCKO= 6.144MHz

Below is the my schematic

  • 0
    TI__Guru 57800 points

    Hi, Sing,

    Welcome to E2E, Thanks for your interest in our products!. 

    We will take a look to your issue and will get back to you as soon as possible.

    Best Regards,

      -Diego Meléndez López
       Audio Applications Engineer

  • 0 in reply to Diego Melendez
    Prodigy 85 points

    Hi Diego,

    Any update finding?

    Thanks

    Sing

  • 0 in reply to Diego Melendez
    Prodigy 85 points
    Hi Diego,

    What is the progress of my issue?
    I'm looking forward to your reply.

    Thanks
    Sing
  • 0 in reply to Sing Lit
    TI__Expert 5645 points
    Hi Sing,
    Sorry for the delayed response.

    Based on your configuration, I see that the MODE=001 which configures the output port as MASTER w RCKI=128fs. This will result in LRCKO= 12.288MHz/128 = 96kHz and not 44.1kHz.

    If you do configure the output port as SLAVE, you should be able to achieve 44.1kHz. Thanks.

    Best regards,
    Ravi
  • 0 in reply to Ravi Patil
    Prodigy 85 points

    Hi Ravi,

    Thanks for reply! You means that when I configure to MODE=000, the BCK, LRCK, DATA of input port routes directly to the output port, the SRC4190 will be like as a data swtich?

    BTW , In my case the MODE=001, what is the SRC4190 doing when Bypass=1? What is purpose and application for this config?

    Thanks!

    Sing

  • 0 in reply to Ravi Patil
    Prodigy 85 points

    Hi Ravi,

    I've configured to output port as SLAVE (MODE=000), but there is nothing output on the output port. Why?

    In my application, the source must be a Master I2S signal, and the DAC must be a Slave. In Dev mode, I need to bypass the SRC the source I2S signal goes direct to the DAC. I want to know is it possible to achieve my application by use BYPAS pin. If not I need to add data switches on the DAC to bypass the SRC. 

    Thanks!

    Sing

  • 0 in reply to Sing Lit
    Guru 36530 points

    Hi Sing-san,

    I also had the same issue in the past.
    As a result of having verified SRC4192 which is the same family with SRC4190, the output serial port format depends on the serial port mode setting even if choosing the bypass mode.
    For the bypass mode, I think that the I2S clocks which are same fs with the input serial port should be input to the output serial port if using both input and output serial ports as the slave mode.

    Best regards,
    Kato

  • 0 in reply to Sadanori Kato
    Prodigy 85 points

    Hi Kato-san,

    Thanks for your advice! I had tried to configure both input and output serial ports to slave mode,but the fs output is not same as input, the output is kept logic low forever.

    Thanks!

    Sing

  • 0 in reply to Sing Lit
    Guru 36530 points

    Hi Sing-san,

    For the normal mode, I2S clocks should be input to the output serial ports if setting the output serial ports as the slave mode, the valid clocks and data are output from the output serial port if choosing the output serial ports as the master mode.
    For the bypass mode, the fs for both input and output serial ports should be same to get the valid data.

    Best regards,
    Kato

  • 0 in reply to Sadanori Kato
    Prodigy 85 points
    Hi Kato-san,

    For the Normal mode, it is clearly stated on the datasheet without doubt.
    But for the Bypass mode, it is ambiguouly.

    Thanks
    Sing
  • 0 in reply to Sing Lit
    Guru 36530 points

    Hi Sing-san,

    I agree with you.

    The evaluation result which I have measured using SRC4192 and PCM5142 in the past is shown as below.

    <SRC4192 Hardware Pin Settings>
    - Output Port is Master Mode with RCKI = 256fs(fs=96kHz Fixed)
    MODE2 = 0
    MODE1 = 1
    MODE0 = 1

    - Input Port Data Format : 24-Bit I2S
    IFMT2 = 0
    IFMT1 = 0
    IFMT0 = 1

    - Output Port Data Format : I2S
    OFMT1 = 0
    OFMT0 = 1

    - Output Port Data Word Length : 24 Bits
    OWL1 = 0
    OWL0 = 0

    - Low Group Delay Control Input : Decimation Filter Enabled
    LGRP = 0

    - TDM Data Input : Not in Use
    TDMI = 0

    - Bypass Mode
    BYPAS = 0(Normal Mode) or 1(Bypass Mode)

    - Input fs
    32kHz to 96kHz@1kHz Sine

    Best regards,
    Kato

  • 0 in reply to Sadanori Kato
    Prodigy 85 points

    Hi Kato-san,

    Thank you for your very helpful information. I understand now.

    Cheers!

    Sing

  • 0 in reply to Sing Lit
    Guru 36530 points

    Hi Sing-san,

    I am honored that I can help you.

    Best regards,
    Kato