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LMX9838 no sound

Vladimir Aparin
Expert 2610 points

I made a headset project based on LMX9838.
I wrote a software that works good on development board LMX9838DONGLE.
But when I made a PCB and LMX9838 samples was soldered there is no sound – no signal on PCM lines of LMX9838 and no signal on Bluetooth headset.

When LMX9838DONGLE soldered to PCB contact pads all’s working good.
Firmware is same in both variants.
Samples and IC in development board has a patch 2 from factory.

What may going wrong? How fix it?

Schematics 3463.схема.pdf

PCB 8802.топология ПП.pdf

Another one question:
Which parameters in EEPROM may affects on audio interface?
Here is no quartz 32kHz on PCB, clocks by internal generator.
CodecType, AirFormat, PcmSlaveConfig и PcmFcprs are setted at start every time (commands SET_PCM_SLAVE_CONFIG and GAP_SET_AUDIO_CONFIG).

  • 0
    TI__Mastermind 32615 points

    Hi,

    Please feel free to contact Lin, Ryan at ryanlin@ti.com directly.

  • 0
    TI__Prodigy 725 points

    Hi Vladimir,

    From the schematic, V_core on pin 9 should not be connected based on Figure 10 (page 25) on the datasheet. I'm just curious if there's a reason to have the 0.1uF and 4.7uF in the first place?

    Also, what's the baudrate you set to run for the UART?

     

    Ryan Lin

  • 0 in reply to Ryan Lin
    Prodigy 40 points

    Hi, Ryan.

    We put Vcore capacitors because they are present in evaluation board scheme (page 28). You think they do not need?

    Baudrate of UART is 115200 (set using pins OP3, OP4, OP5).

  • 0 in reply to Bass
    TI__Prodigy 725 points

    Hi Bass,

    Yes, the EVM was only for evaluation purposes. You are using a 3.3V source, so let's follow the Figure 10 in the datasheet page 25, including the decoupling caps.

    Please help update your designs accordingly, and I am checking to see if there are any other points we can debug on.

    Thanks.

    Ryan Lin

  • 0 in reply to Ryan Lin
    Prodigy 40 points

    Thank you Ryan.

    We will fix the scheme and remove all capacitors on Vcore.

    But what about PCM problem? I Initializes audio using commands SET_PCM_SLAVE_CONFIG
    - use slot 1
    - 2 slots
    - 16 bit linear
    - long frame sync
    - 16-bit data word length
    - use inverted frame sync
    - Fcprs = 31
    and GAP_SET_AUDIO_CONFIG (PCM Slave, CVSD) at every restart of the module. But sound did not work.

    To solve the problem I reinitialize almost all parameters in the EEPROM on the default values. I use command SET_DEFAULT_AUDIO_CONFIG (PCM Slave, CVSD) and save settings PCM slave in EEPROM:
    - use slot 0
    - 1 slots
    - 16 bit linear
    - long frame sync
    - 16-bit data word length
    - use normal frame sync
    - Fcprs =31.
    Do you have any ideas on this?

  • 0 in reply to Bass
    TI__Prodigy 725 points

    Hi Bass,

    I have replied to Vladimir Aparin's email on this. Please let me know if you get the response.

    My email is ryanlin@ti.com, feel free to contact me directly.

    Ryan Lin