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PCM1808: Customer would like to use PCM1808 for the beep sound solution on PC

George Liu1
Intellectual 1570 points
Part Number: PCM1808
Other Parts Discussed in Thread: , PCM1840, TLV320ADC3140

Hi Sir,

Customer would like to design PCM1808 for the beep sound solution on PC, here got some questions would need your help to re-confirm their idea.

1. If the beep signal from PCH for the PCM1808 input is PWM signal, did they need to add the RC filter (Low pass filter) before the input side? 

2. If the beep signal come from PCH is mono, could they only connect the L channel, or you suggest them to connect both L & R directly?

3. If they would need PCM1808 become the Master, would SCKI be necessary?

4. If customer would need to cut the PCM1808 output, would you suggest them to cut the power directly? If so, did they need to cut off both Vdd/Vcc or either one will be ok? 

5. If we are not suggest them to cut off the power for disable PCM1808, not sure add load switch on input (analog) will be much confidence?

I can send the simple block diagram by email...

Looking forward to hearing from you soon, any comments will be appreciated.

Thanks,

George

  • 0
    TI__Guru 63965 points

    Hi George,

    1. If the beep signal from PCH for the PCM1808 input is PWM signal, did they need to add the RC filter (Low pass filter) before the input side? 

    Yes, the ideal input signal to the PCM1808 is an analog signal, so while the internal decimator will likely perform some of this function for you, the performance will be tremendously improved if you add a 2nd-order (or higher) Low-pass before the ADC.

    2. If the beep signal come from PCH is mono, could they only connect the L channel, or you suggest them to connect both L & R directly?

    Connecting only to the L channel is fine.  Terminate the R channel by connecting it to GND through a 0.47uF capacitor, this prevents it from floating and picking up noise that may disturb the active channel.

    3. If they would need PCM1808 become the Master, would SCKI be necessary?

    Yes, a master clock input will need to be provided through the SCKI pin.  Review the information on the PCM1808EVM schematic for an example crystal oscillator based solution.  An external clock from a processor will also be acceptable, but generating the correct frequencies may be difficult.

    4. If customer would need to cut the PCM1808 output, would you suggest them to cut the power directly? If so, did they need to cut off both Vdd/Vcc or either one will be ok? 

    The desired operation to put the device in reset or a low-power mode is to cut the system clocks as defined in the datasheet.  Cutting power abruptly may cause some undesired audio.

    5. If we are not suggest them to cut off the power for disable PCM1808, not sure add load switch on input (analog) will be much confidence?

    See above, recommended to cut the clocks to the device.

    I can send the simple block diagram by email...

    Looking forward to hearing from you soon, any comments will be appreciated.

  • 0 in reply to Collin Wells
    TI__Intellectual 1570 points

    Hi Collin,

    Thanks for your reply, it make more clear for me.

    BTW, if we cut SCLK... it will keep PCM1808 become low-power mode. Ideal power but if they would like to shutdown the PCM1808 for more aggressive power saving, could they cut-off the SCLK firstly and then cut all the power rail for PCM1808?

    BTW, just curious... is there any other suggestion candidates which similar to PCM1808 but no need SCLK?

    Thanks,

    George

  • 0 in reply to George Liu1
    TI__Guru 63965 points

    Hi George,

    Yes, this sounds like a good method for aggressive power-savings.  Make sure the customer reviews some of the soft-stepping information in the datasheet to understand rough timings for the power-down/off behaviors.

    PCM1840 is our newest HW controlled device and can operate in a 3-wire ASI mode.

  • 0 in reply to Collin Wells
    TI__Intellectual 1570 points

    Hi Collin,

    Thanks for sharing, I got one more question.

    When we cut-off the SCLK, what is the status of our BCK/LRCK/DOUT? Would it influence the other device which would use the same i2s bus?

    If we cut-down the power rail what is the status of PCM1808 i2s? 

    Thanks,

    George

  • 0 in reply to George Liu1
    TI__Guru 63965 points

    Hi George,

    You may want to look into an ADC with a dedicated SW or HW power-down function in this case since the bus is shared with other devices.  It is not advised to apply ASI signals to the PCM1808 while it's not powered.

    Take a look at the PCM186x family or the newer TLV320ADC3140 device.