Datasheet

PCM3070
SLAS724 – FEBRUARY 2011 www.ti.com
• Fast charge of ac-coupling capacitors
• Anti thump
Analog Bypass
The PCM3070 offers two analog-bypass modes. In either of the modes, an analog input signal can be routed
from an analog input pin to an amplifier driving an analog output pin. Neither the ADC nor the DAC resources are
required for such operation.
In analog low-power bypass mode, line-level signals can be routed directly from the analog inputs INL to the left
headphone amplifier (HPL) and INR to HPR.
ADC Bypass Using Mixer Amplifiers
In addition to the analog bypass mode, there is a bypass mode that uses the programmable gain amplifiers of
the input stage in conjunction with a mixer amplifier. With this mode, low-level signals can be amplified and
routed to the line or headphone outputs, fully bypassing the ADC and DAC.
To enable this mode, the mixer amplifiers are powered on via software command.
Headphone Outputs
The stereo headphone drivers on pins HPL and HPR can drive loads with impedances down to 16Ω in
single-ended AC-coupled headphone configurations, or loads down to 32Ω in differential mode, where a speaker
is connected between HPL and HPR. In single-ended drive configuration these drivers can drive up to 15mW
power into each headphone channel while operating from 1.8V analog supplies. While running from the AVdd
supply, the output common-mode of the headphone driver is set by the common-mode setting of analog inputs in
Page 1 / Register 10, Bit D6, to allow maximum utilization of the analog supply range while simultaneously
providing a higher output-voltage swing. In cases when higher output-voltage swing is required, the headphone
amplifiers can run directly from the higher supply voltage on LDOIN input (up to 3.6V). To use the higher supply
voltage for higher output signal swing, the output common-mode can be adjusted to either 1.25V, 1.5V or 1.65V
by configuring Page 1 / Register 10, Bits D5-D4. When the common-mode voltage is configured at 1.65V and
LDOIN supply is 3.3V, the headphones can each deliver up to 40mW power into a 16Ω load.
The headphone drivers are capable of driving a mixed combination of DAC signal and bypass from analog input
INL and INR by configuring Page 1 / Register 12 and Page 1 / Register 13 respectively. The analog input signals
can be attenuated up to 72dB before routing by configuring Page 1 / Register 22 and 23. The level of the DAC
signal can be controlled using the digital volume control of the DAC in Page 0, Reg 65 and 66. To control the
output-voltage swing of headphone drivers, the digital volume control provides a range of –6.0dB to +29.0dB
(6)
in
steps of 1dB. These can be configured by programming Page 1 / Register 16 and 17. These level controls are
not meant to be used as dynamic volume control, but more to set output levels during initial device configuration.
Refer to for recommendations for using headphone volume control for achieving 0dB gain through the DAC
channel with various configurations.
Line Outputs
The stereo line level drivers on LOL and LOR pins can drive a wide range of line level resistive impedances in
the range of 600Ω to 10kΩ. The output common modes of line level drivers can be configured to equal either the
analog input common-mode setting or to 1.65V. With output common-mode setting of 1.65V and DRVdd_HP
supply at 3.3V the line-level drivers can drive up to 1Vrms output signal. The line-level drivers can drive out a
mixed combination of DAC signal and attenuated ADC PGA signal. Signal mixing is register-programmable.
ADC
The PCM3070 includes a stereo audio ADC, which uses a delta-sigma modulator with a programmable
oversampling ratio, followed by a digital decimation filter. The stereo recording path can be powered up one
channel at a time, to support the case where only mono record capability is required.
The ADC path of the PCM3070 features a large set of options for signal conditioning as well as signal routing:
• 2 ADCs
• 6 analog inputs which can be mixed and/or multiplexed in single-ended and/or differential configuration
(6) If the device must be placed into 'mute' from the –6.0dB setting, set the device at a gain of –5.0dB first, then place the device into mute.
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