LM4550B National Semiconductor Corporation, LM4550B Datasheet - Page 12

• Manufacturer Part Number: LM4550B
• Description: Ac 97 Rev 2.1 Multi-channel Audio Codec With Stereo Headphone Amplifier, Sample Rate Conversion And National 3d Sound
• Manufacturer: National Semiconductor Corporation

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SDATA_OUT
Pin Descriptions
SDATA_IN
HP_OUT_C
HP_OUT_R
HP_OUT_L
XTL_OUT
BIT_CLK
XTL_IN
Name
Name
Pin
2
3
5
6
8
Pin
39
40
41
I / O
I / O
I/O
O
O
I
I
O
O
I
(Continued)
Functional Description
Left Stereo Channel Output
This line level output (1 Vrms nominal) is fed from the left channel of the Stereo Mix signal
from MIX2 via the Headphone Volume register, 04h. The HP_OUT_L amplitude can be muted
(along with HP_OUT_R) or adjusted from 0 dB to - 46.5 dB in 1.5 dB steps
AC Ground Reference
In normal use, this input is the AC ground reference for HP_OUT_L and HP_OUT_R. It must
be capacitively coupled to analog ground with short traces to maximize performance. It is
NOT a DC ground.
For non-stereo applications it may also be used to provide common-mode feedback with
HP_OUT configured as one differential output rather than as outputs for two single-ended
stereo channels.
Right Stereo Channel Output
This line level output (1 Vrms nominal) is fed from the right channel of the Stereo Mix signal
from MIX2 via the Headphone Volume register, 04h. The HP_OUT_R amplitude can be muted
(along with HP_OUT_L) or adjusted from 0 dB to - 46.5 dB in 1.5 dB steps
24.576 MHz crystal or external oscillator input
To complete the oscillator circuit use a fundamental mode crystal operating in parallel
resonance and connect a 1MΩ resistor across pins 2 and 3. Choose the load capacitors
(Figure 2, C1, C2) to suit the load capacitance required by the crystal (e.g. C1 = C2 = 33 pF
for a 20 pF crystal. Assumes that each ’Input + trace’ capacitance is 7 pF).
This pin may also be used as the input for an external oscillator (24.576 MHz nominal) at
standard logic levels (V
This pin is only used when the codec is in Primary mode. It may be left open (NC) for any
Secondary mode.
24.576 MHz crystal output
Used with XTAL_IN to configure a crystal oscillator.
When the codec is used with an external oscillator this pin should be left open (NC).
When the codec is configured in a Secondary mode this pin is not used and may be left open
(NC).
Input to codec
This is the input for AC Link Output Frames from an AC ’97 Digital Audio Controller to the
LM4550B codec. These frames can contain both control data and DAC PCM audio data. This
input is sampled by the LM4550B on the falling edge of BIT_CLK.
AC Link clock
An OUTPUT when in Primary Codec mode. This pin provides a 12.288 MHz clock for the AC
Link. The clock is derived (internally divided by two) from the 24.576 MHz signal at the crystal
input (XTL_IN).
This pin is an INPUT when the codec is configured in any of the Secondary Codec modes
and would normally use the AC Link clock generated by a Primary Codec.
Output from codec
This is the output for AC Link Input Frames from the LM4550B codec to an AC ’97 Digital
Audio Controller. These frames can contain both codec status data and PCM audio data from
the ADCs. The LM4550B clocks data from this output on the rising edge of BIT_CLK.
DIGITAL I/O AND CLOCKING
ANALOG I/O (Continued)
IH
, V
IL
12
).
Functional Description