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PCM1690-Q1: Question about External component and sequence

Yuta Kurimoto
Genius 9855 points
Part Number: PCM1690-Q1

Hello Team,

I got question from customer as below. Can you please provide answer?

Q1. Can you please let me know the min/max value of internal pull-down resistor of LRCK, BCK, RST, MS/ADR0/RSV pins? This is because in the customer's circuit these pins are connected with their audio DSP. The DSP has internal pull-up resistor so they want to know the pull-down resistors' min/max value.

Q2. Regarding with BCK, LRCK pin, Can they put 2,2kohm or 4.7kohm pull-up resistor for external of these pin? 

Q3. Datasheet recommend the VCOM capacitor is 10uF. In case customer changes the capacitance, what's happen?

Q4. In the customer's circuit, the sequence is below. The RST is firstly pull-up but will be pull-down for longer than 100ms. After that The SCKI is input. Is this sequence any problem?

Thanks,

Yuta Kurimoto

  • 0
    TI__Guru 53663 points

    Hi Kurimoto-san,

    1.  The min/max of the resistor value was not characterized, but I would expect the value to be within ±20% of the nominal value.

    2. The BCK and LRCK are digital inputs of this device, so the pull-up values would not have much impact on its operation.  These values are okay from the DAC perspective.  It should be noted that when they are driven by the I2S source, those digital outputs will have to drive this resistance.  It will add current transients on the digital domain and digital ground return path.

    3. The VCOM pin is a reference voltage for the DAC outputs that is created by a simple resistor divider.  The larger the capacitor, the lower frequency the fC of this filter is, which will help limit the noise in the audible band.  I believe the resistor divider is created by two 15kΩ resistors.  From a noise perspective, these would be in parallel, so you have R=7.5kΩ for the RC filter.  Changing the cap value will determine the cutoff frequency. 10µF will have an fC of about 2.1Hz, while C=1µF will have an fC =21Hz.  This might be well below the audible range for their application, so it might not be an issue.  larger capacitor values also slow the ramp time of VCOM, which will limit the time from power-on before the device can play audio.

    4. I recommend that they assert RESET until the SCLK starts, though there is not a bit risk to use the device in the proposed way, 

    Thanks

    Paul