Datasheet

ADAU1772 Data Sheet
Rev. B | Page 34 of 116
OUTPUT SIGNAL PATHS
Data from the serial input port can be routed to the core either
directly or through a sample rate converter. Data can be routed
to the serial output port, the stereo DAC, and the stereo PDM
modulator.
The analog outputs of the ADAU1772 can be configured as
differential or single-ended outputs. The analog output pins are
capable of driving headphone or earpiece speakers. The line
outputs can drive a load of at least 10 kΩ or can be put into
headphone mode to drive headphones or earpiece speakers. The
analog output pins are biased at AVDD/2.
ANALOG OUTPUTS
Headphone Output
The output pins can be driven by either a line output driver or a
headphone driver by setting the HP_EN_L and HP_EN_R bits
in the headphone line output select register (Address 0x0043).
The headphone outputs can drive a load of at least 16 Ω.
Headphone Output Power-Up Sequencing
To prevent pops when turning on the headphone outputs, the
user must wait at least 6 ms to unmute these outputs after enabling
the headphone output using the HP_EN_x bits. Waiting 6 ms
allows an internal capacitor to charge before these outputs are
used. Figure 73 illustrates the headphone output power-up
sequencing.
Figure 73. Headphone Output Power-Up Timing
Ground-Centered Headphone Configuration
The headphone outputs can also be configured as ground-
centered outputs by connecting coupling capacitors in series
with the output pins. Ground-centered headphones should use
the AGND pin as the ground reference.
When the headphone outputs are configured in this manner,
the capacitors create a high-pass filter on the outputs. The
corner frequency of this filter, which has an attenuation of 3 dB
at this point, is calculated by the following formula:
f
3dB
= 1/(2π × R × C)
where :
R is the impedance of the headphones.
C is the capacitor value.
For a typical headphone impedance of 32 Ω and a 220 μF
capacitor, the corner frequency is 23 Hz.
Pop-and-Click Suppression
On power-up, the precharge circuitry is enabled on all four
analog output pins to suppress pops and clicks. After power-
up, the precharge circuitry can be put into a low power mode
using the HP_POP_DISx bits in the POP_SUPRRESS register
(Address 0x0029).
The precharge time depends on the value of the capacitor
connected to the CM pin and the RC time constant of the load
on the output pin. For a typical line output load, the precharge
time is between 2 ms and 3 ms. After this precharge time, the
HP_POP_DISx bit can be set to low power mode.
To avoid clicks and pops, all analog outputs that are in use should
be muted while changing any register settings that may affect the
signal path. These outputs can then be unmuted after the changes
have been made.
Line Outputs
The analog output pins (HPOUTLP/LOUTLP, HPOUTLN/
LOUTLN, HPOUTRP/LOUTRP, and HPOUTRN/LOUTRN)
can be used to drive both differential and single-ended loads. In
their default settings, these pins can drive typical line loads of
10 kΩ or greater.
When the line output pins are used in single-ended mode, the
HPOUTLP/LOUTLP and HPOUTRP/LOUTRP pins should be
used to output the signals, and the HPOUTLN/LOUTLN and
HPOUTRN/LOUTRN pins should be powered down.
DIGITAL-TO-ANALOG CONVERTERS
The ADAU1772 includes two 24-bit Σ-Δ digital-to-analog
converters (DACs).
DAC Full-Scale Level
The full-scale output from the DACs (0 dBFS) scales linearly with
AVDD. At AV DD = 3.3 V, the full-scale output level is 1.94 V rms
for a differential output or 0.97 V rms for a single-ended output.
Digital DAC Volume Control
The volume of each DAC can be digitally attenuated using the
DACx_VOLUME registers (Address 0x002F and Address 0x0030).
The volume can be set to be between 0 dB and −95.625 dB in
0.375 dB steps.
PDM OUTPUT
The ADAU1772 includes a 2-channel pulse density modulated
(PDM) modulator. The PDMOUT pin can be used to drive a PDM
input amplifier, such as the SSM2517 mono 2.4 W amplifier. Two
SSM2517 devices can be connected to the PDMOUT data stream
to enable a stereo output. The PDM output signal is clocked by the
CLKOUT pin output. The PDM output stream must be clocked
by this pin and not by a clock from another source, such as another
audio IC, even if the other clock is of the same frequency as
CLKOUT. The PDM output data is clipped at the −6 dB level to
prevent overdriving a connected amplifier like the SSM2517.
HP_EN_X
1 = HEADPHONE
HP_MUTE_R AND HP_MUTE_L
00 = UNMUTE
INTERNAL
PRECHARGE
6ms
USER
DEFINED
10804-066