lm4546a National Semiconductor Corporation, lm4546a Datasheet - Page 10

• Manufacturer Part Number: lm4546a
• Description: Ac ?97 Rev 2 Multi-channel Audio Codec With Sample Rate Conversion And National 3d Sound
• Manufacturer: National Semiconductor Corporation

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Pin Descriptions
LINE_IN_R
LINE_IN_L
CD_GND
Name
CD_R
MIC1
MIC2
Pin
19
20
21
22
23
24
I / O
I
I
I
I
I
I
(Continued)
Functional Description
AC Ground Reference
This input is the reference for the signals on both CD_L and CD_R. CD_GND is NOT a DC
ground and should be AC-coupled to the stereo source ground common to both CD_L and
CD_R. The three inputs CD_GND, CD_L and CD_R act together as a quasi-differential stereo
input with CD_GND providing AC common-mode feedback to reject ground noise. This can
improve the input SNR for a stereo source with a good common ground but precision
resistors may be needed in any external attenuators to achieve the necessary balance
between the two channels.
Right Stereo Channel Input
This line level input (1 Vrms nominal) is selectable at the right channel of the stereo Input
Mux for conversion by the right channel ADC. It can also be mixed into the right channel of
the Stereo Mix 3D signal at MIX1 under the control of the CD Volume register, 12h. The
CD_R level can be muted (along with CD_L) or adjusted from +12 dB to -34.5 dB in 1.5 dB
steps. Stereo Mix 3D is combined into the Stereo Mix signal at MIX2 for access to the stereo
outputs Line Out and Line Level Out.
Mono microphone input
Either MIC1 or MIC2 can be muxed to a programmable boost amplifier with selection by the
MS bit (bit D8) in the General Purpose register, 20h. The boost amplifier gain (0 dB or 20 dB)
is set by the 20dB bit (D6) in the Mic Volume register, 0Eh. Nominal input levels at the two
gain settings are 1 Vrms and 0.1 Vrms respectively. The amplifier output is selectable (Record
Select register, 1Ah) by either the right or left channels of the Record Select Mux for
conversion on either or both channels of the stereo ADCs. The amplifier output can also be
accessed at the stereo mixer MIX1 (muting and mixing adjustments via Mic Volume register,
0Eh) where it is mixed equally into both left and right channels of Stereo Mix 3D for access to
the stereo outputs Line Out and Line Level Out. Access to the Mono analog output is
selected by a mux controlled by the MIX bit (D9) in General Purpose register, 20h.
Mono microphone input
Either MIC1 or MIC2 can be muxed to a programmable boost amplifier with selection by the
MS bit (bit D8) in the General Purpose register, 20h. The boost amplifier gain (0 dB or 20 dB)
is set by the 20dB bit (D6) in the Mic Volume register, 0Eh. Nominal input levels at the two
gain settings are 1 Vrms and 0.1 Vrms respectively. The amplifier output is selectable (Record
Select register, 1Ah) by either the right or left channels of the Record Select Mux for
conversion on either or both channels of the stereo ADCs. The amplifier output can also be
accessed at the stereo mixer MIX1 (muting and mixing adjustments via Mic Volume register,
0Eh) where it is mixed equally into both left and right channels of Stereo Mix 3D for access to
the stereo outputs Line Out and Line Level Out. Access to the Mono analog output is
selected by a mux controlled by the MIX bit (D9) in General Purpose register, 20h.
Left Stereo Channel Input
This line level input (1 Vrms nominal) is selectable at the left channel of the stereo Record
Select Mux for conversion by the left channel ADC. It can also be mixed into the left channel
of the Stereo Mix 3D signal at MIX1 under the control of the Line In Volume register, 10h. The
LINE_IN_L level can be muted (along with LINE_IN_R) or adjusted from +12 dB to -34.5 dB
in 1.5 dB steps. Stereo Mix 3D is combined into the Stereo Mix signal at MIX2 for access to
the stereo outputs Line Out and Line Level Out.
Right Stereo Channel Input
This line level input (1 Vrms nominal) is selectable at the right channel of the stereo Input
Mux for conversion by the right channel ADC. It can also be mixed into the right channel of
the Stereo Mix 3D signal at MIX1 under the control of the Line In Volume register, 10h. The
LINE_IN_R level can be muted (along with LINE_IN_L) or adjusted from +12 dB to -34.5 dB
in 1.5 dB steps. Stereo Mix 3D is combined into the Stereo Mix signal at MIX2 for access to
the stereo outputs Line Out and Line Level Out.
ANALOG I/O (Continued)
10