LM1972M - Digitally Controlled 2-Channel Audio Attenuator

Overview

The LM1972M is a high-performance, digitally controlled 2-channel audio attenuator fabricated using CMOS technology. Designed for precision audio applications, this IC provides exceptional attenuation control with fine resolution steps and a wide dynamic range. The device features a logarithmic attenuation curve that can be customized to meet specific system requirements, making it ideal for professional audio equipment, mixing consoles, and high-fidelity systems.

With its 3-wire serial interface, the LM1972M offers straightforward digital control while maintaining excellent analog signal integrity. Each channel operates independently, allowing for precise stereo balance control or dual mono applications.

Key Features

• Dual-Channel Operation: Independent control of two audio channels
• Precision Attenuation: 0.5dB steps from 0dB to 47.5dB, 1.0dB steps from 48dB to 78dB
• Deep Mute Function: 104dB attenuation when muted
• Customizable Attenuation Curve: Logarithmic response can be tailored to application needs
• 3-Wire Serial Interface: Simple digital control interface (CLK, DATA, LE)
• Wide Supply Voltage Range: Operates from ±2.5V to ±17V
• Low Distortion: Maintains signal integrity even at maximum attenuation
• High Channel Separation: Minimizes crosstalk between channels
• CMOS Technology: Low power consumption and high reliability

Applications

The LM1972M is suitable for a wide range of professional and consumer audio applications including:

• Professional audio mixing consoles
• Digital audio workstations (DAWs)
• Home theater systems
• Automotive audio systems
• Broadcast equipment
• Musical instruments and effects processors
• PA systems and amplifiers
• Audio test and measurement equipment

Electrical Characteristics

Absolute Maximum Ratings

• Supply Voltage (V+ to V-): ±17V
• Digital Input Voltage: -0.3V to V+ +0.3V
• Operating Temperature Range: -40°C to +85°C
• Storage Temperature Range: -65°C to +150°C

Recommended Operating Conditions

• Supply Voltage Range: ±2.5V to ±17V
• Analog Input Voltage: ±(VSUPPLY - 2V)
• Clock Frequency: 10MHz max
• Operating Temperature: -40°C to +85°C

Performance Characteristics (Typical @ ±15V, 25°C)

• Total Harmonic Distortion + Noise: 0.003% @ 1kHz, 0dB attenuation
• Signal-to-Noise Ratio: 120dB (unweighted)
• Channel Separation: 90dB @ 1kHz
• Frequency Response: ±0.1dB, 20Hz to 20kHz
• Attenuation Accuracy: ±0.25dB typical
• Power Consumption: 15mA per channel

Package Information

SOIC-16 Package

• Package Type: 16-Lead Small Outline Integrated Circuit (SOIC)
• Package Dimensions: 9.90mm x 3.90mm body
• Lead Pitch: 1.27mm
• Lead Count: 16
• Mounting Style: Surface Mount
• RoHS Compliant: Yes

Functional Description

The LM1972M operates as a digitally controlled analog attenuator. The device accepts serial data through its 3-wire interface (Clock, Data, and Latch Enable) to set the attenuation level for each channel independently. The attenuation follows a precise logarithmic curve, providing natural-sounding volume control that matches human hearing perception.

Each channel's attenuation register is 8 bits wide, allowing for 256 possible attenuation settings. The actual attenuation follows a segmented curve with 0.5dB steps for fine control at lower attenuation levels and 1.0dB steps for coarser control at higher attenuation levels.

Interface Protocol

The 3-wire serial interface operates as follows:

• Data (DIN): 16-bit serial data word (MSB first)
• Clock (CLK): Rising edge triggered data clock
• Latch Enable (LE): Active high signal to transfer data to attenuation registers

The 16-bit data word consists of:

• Bits 15-8: Channel 1 attenuation data
• Bits 7-0: Channel 2 attenuation data

Design Considerations

Power Supply Decoupling

For optimal performance, place 0.1μF ceramic capacitors as close as possible to the power supply pins, with additional 10μF electrolytic capacitors for bulk decoupling.

PCB Layout Guidelines

• Keep analog and digital grounds separate, connecting at a single point
• Minimize trace lengths for analog signal paths
• Use ground planes for improved noise immunity
• Route digital control signals away from analog signal paths

Ordering Information

• LM1972M/NOPB: SOIC-16, Tape and Reel
• LM1972MX/NOPB: SOIC-16, 2500 unit reel