LM1972

General Description

The LM1972 is a digitally controlled 2-channel 78dB audio

attenuator fabricated on a CMOS process. Each channel

has attenuation steps of 0.5dB from 0dB–47.5dB, 1.0dB

steps from 48dB–78dB, with a mute function attenuating

104dB. Its logarithmic attenuation curve can be customized

through software to fit the desired application.

The performance of a µPot is demonstrated through its ex-

cellent Signal-to-Noise Ratio, extremely low (THD+N), and

high channel separation. Each µPot contains a mute function

that disconnects the input signal from the output, providing a

minimum attenuation of 96dB. Transitions between any at-

tenuation settings are pop free.

The LM1972’s 3-wire serial digital interface is TTL and

CMOS compatible; receiving data that selects a channel and

the desired attenuation level. The Data-Out pin of the

LM1972 allows multiple µPots to be daisy-chained together,

reducing the number of enable and data lines to be routed

for a given application.

Key Specifications

n Total Harmonic Distortion + Noise:

0.003% (max)

n Frequency response:

100 kHz (−3dB) (min)

n Attenuation range (excluding mute):

78dB (typ)

n Differential attenuation:

n Signal-to-noise ratio (ref. 4 Vrms):

110dB (min)

n Channel separation:

100dB (min)

Features

n 3-wire serial interface

n Daisy-chain capability

n 104dB mute attenuation

n Pop and click free attenuation changes

Applications

n Automated studio mixing consoles

n Music reproduction systems

n Sound reinforcement systems

n Electronic music (MIDI)

n Personal computer audio control

Typical Application

Connection Diagram

DS011978-1

FIGURE 1. Typical Audio Attenuator Application Circuit

Dual-In-Line Plastic or

Surface Mount Package

DS011978-2

Top View

Order Number LM1972M or LM1972N

See NS Package Number M20B or N20A

April 1995

© 1999 National Semiconductor Corporation

DS011978

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