Datasheet

ANALOG INPUT BYPASS PATH FUNCTIONALITY
ADC PGA SIGNAL BYPASS PATH FUNCTIONALITY
INPUT IMPEDANCE AND VCM CONTROL
MICBIAS GENERATION
PASSIVE ANALOG BYPASS DURING POWER DOWN
TLV320AIC3101
SLAS520D – FEBRUARY 2007 – REVISED DECEMBER 2008 ........................................................................................................................................ www.ti.com
The TLV320AIC3101 includes the additional ability to route some analog input signals past the integrated data
converters, for mixing with other analog signals and then direct connection to the output drivers. This capability is
useful in a cellphone, for example, when a separate FM radio device provides a stereo analog output signal that
needs to be routed to headphones. The TLV320AIC3101 supports this in a low-power mode by providing a direct
analog path through the device to the output drivers, while all ADCs and DACs can be completely powered down
to save power.
When programmed correctly, the device can pass the LINE2L and LINE2R signals directly to the output stage.
In addition to the input bypass path described previously, the TLV320AIC3101 also includes the ability to route
the ADC PGA output signals past the ADC, for mixing with other analog signals and then direct connection to the
output drivers. These bypass functions are described in more detail in the sections on output mixing and output
driver configurations.
The TLV320AIC3101 includes several programmable settings to control analog input pins, particularly when they
are not selected for connection to an ADC PGA. The default option allows unselected inputs to be put into a
high-impedance state, such that the input impedance seen looking into the device is extremely high. Note,
however, that the pins on the device do include protection diode circuits connected to AVDD and AVSS. Thus, if
any voltage is driven onto a pin approximately one diode drop (~0.6 V) above AVDD or one diode drop below
AVSS, these protection diodes begin conducting current, resulting in an effective impedance that no longer
appears as a high-impedance state.
Another programmable option for unselected analog inputs is to weakly hold them at the common-mode input
voltage of the ADC PGA (which is determined by an internal band-gap voltage reference). This is useful to keep
the ac-coupling capacitors connected to analog inputs biased up at a normal dc level, thus avoiding the need for
them to charge up suddenly when the input is changed from being unselected to selected for connection to an
ADC PGA. This option is controlled in page 0, registers 20 and 23. The user should ensure this option is
disabled when an input is selected for connection to an ADC PGA or selected for the analog input bypass path,
because it can corrupt the recorded input signal if left operational when an input is selected.
In most cases, the analog input pins on the TLV320AIC3101 should be ac-coupled to analog input sources, the
only exception to this generally being if an ADC is being used for dc voltage measurement. The ac-coupling
capacitor causes a high-pass filter pole to be inserted into the analog signal path, so the size of the capacitor
must be chosen to move that filter pole sufficiently low in frequency to cause minimal effect on the processed
analog signal. The input impedance of the analog inputs when selected for connection to an ADC PGA varies
with the setting of the input level control, starting at approximately 20 k Ω with an input level control setting of 0
dB, and increasing to approximately 80 k Ω when the input level control is set at – 12 dB. For example, using a
0.1- µ F ac-coupling capacitor at an analog input results in a high-pass filter pole of 80 Hz when the 0-dB input
level control setting is selected.
The TLV320AIC3101 includes a programmable microphone bias output voltage (MICBIAS), capable of providing
output voltages of 2 V or 2.5 V (both derived from the on-chip band-gap voltage) with 4-mA output current drive.
In addition, the MICBIAS may be programmed to be switched to AVDD directly through an on-chip switch, or it
can be powered down completely when not needed, for power savings. This function is controlled by register
programming in page 0, register 25.
Programming the TLV320AIC3101 to passive analog bypass occurs by configuring the output stage switches for
passthrough. This is done by opening switches SW-L0, SW-L3, SW-R0, and SW-R3 and closing either SW-L1 or
SW-L2 and SW-R1 or SW-R2. See Figure 30 . Programming this mode is done by writing to page 0, register 108.
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