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PCM2906C external line regulator for VCCCI

Bjoern Schuster
Prodigy 30 points
Other Parts Discussed in Thread: PCM2906C, REG103

Why is the VCCCI pin at PCM2906C externally powered in EVM and TYPICAL CIRCUIT CONNECTION 1?

Is the internal 3.3V voltage generator not powerful enough for "high-performance application" or too noisy?

If so, when is High-Performance Application reached and I will need an external LDO?

  • 0
    TI__Guru** 109415 points
    Hi Bjoern,

    Welcome to E2E and thank you for your interest in out products!

    That's right, when the VCCCI pin is externally powered the PCM2906C is on high performance. The difference between normal performance and high performance it's highlighted in THD+N (data sheet page 4).
    To use the high performance mode you need to follow the Typical Circuit 1 or the EVM. The regulator must provide 500mA to the VCCCI pin, you can use the suggested regulator (REG103xA-A).
    Hope this help you.

    Best regards,
    Iván Salazar
    Texas Instruments
  • 0 in reply to Ivan Salazar
    Prodigy 30 points
    Hi Iván,
    thanks for your fast reply. I have overseen this in datasheet.
    Not at any time the VCCCI pin needs 500mA at 3.67V external supply voltage. Especially the diode on EVM has an absolute maximum rating of 200mA. What is the real current into VCCCI pin?
    A low noice 100mA LDO in SOT23-5 should do the same, right?
    Best Regards
    Bjoern
  • 0 in reply to Bjoern Schuster
    TI__Guru** 109415 points
    Hi Bjoern,

    Sorry I gave you the regulator specification.
    Yes a low noise LDO 100mA should work fine. I have measured the current in VCCCI pin and it is around 80mA

    Regards,
    Iván Salazar
    Texas Instruments
  • 0 in reply to Ivan Salazar
    Prodigy 30 points
    Hi Iván,

    thanks for the measurement. One last question for final understanding. Why is there the diode?
    Normally it is not a usual way to shorten two outputs of supplies. The transistor of PCM2906s internal line regulator will turned off when output voltage is higher than desired and the external power supply should take care of absolute maximum rating of 4V for VCCCI.
    The external line regulator REG103 (or any other low noise LDO) generates a stable voltage above the maximum internal regulator voltage of 3.5V. The diode makes sense when e.g. at startup sequence the external regulator comes ready later than the internal regulator. In this case I could have a high current flow thru inherent diode in MOSFET of external regulator, when it is self powered and the audio codec is bus-powered... don't care.
    The diode won't disturb when the VCCCI current is quite stable - the voltage drop rises up with at higher current.

    Regards
    Björn