December 1994
LMC1992 Digitally-Controlled Stereo Tone and Volume
Circuit with Four-Channel Input-Selector
General Description
Features
Y
Low noise and distortion
The LMC1992 is a monolithic integrated circuit that provides
four stereo inputs, bass and treble tone controls, and vol-
ume, balance, and front-rear fader controls. These functions
are digitally controlled through a three-wire communication
interface. All of the LMC1992s functions are achieved with
only three external capacitors per channel. It is designed for
Y
Four stereo inputs
Y
40 volume levels including mute
Y
20 fader levels
Y
All attenuators have a 2 dB of attenuation per step
Y
Front/back fade control
b
line level input signals (300 mV
gain of 0 dB.
2V) and has a maximum
Y
External processor loop
Y
Only three external components per channel
Serial programmable: standard MICROWIRETM
interface
The internal design is optimized for external capacitors hav-
ing values of 0.1 mF or less. This allows the use of chip
capacitors for coupling and tone control functions.
Y
Y
Single supply operation: 6V to 12V supply voltage
Low noise and distortion result from using analog switches
and thin-film silicon-chromium resistor networks in the sig-
nal path.
Y
Protection address (similar to DS8906)
Y
DC-coupled inputs
Y
Single supply operation
Volume and fader are at minimum and tone controls are flat
when supply voltage is first applied.
Applications
Y
Additional tone control can be achieved using the LMC835
stereo 7-band graphic equalizer connected to the
LMC1992’s select-out/select-in external processor loop.
Automotive audio systems
Y
Sound reinforcement systems
Y
Home entertainmentÐstereo television and music re-
production systems
Y
Electronic music (MIDI)
Block and Connection Diagrams
TL/H/10789–2
Order Number LMC1992CCN
See NS Package Number N28B
TL/H/10789–1
Left channel shown. Pin numbers in parentheses are for the right channel.
DNRÉ is a registered trademark of National Semiconductor Corporation.
COPSTM and MICROWIRETM are trademarks of National Semiconductor Corporation.
C
1995 National Semiconductor Corporation
TL/H/10789
RRD-B30M75/Printed in U. S. A.