LM1972N

Audio Special Purpose Overview

The LM1972N is a digitally controlled dual-channel audio attenuator fabricated on a CMOS process, housed in a 20-lead SOIC (DW) package. It provides a typical attenuation range of 78 dB with steps of 0.5 dB from 0 to 47.5 dB and 1.0 dB from 48 to 78 dB. A mute function achieves 104 dB attenuation. Key electrical specifications include a maximum Total Harmonic Distortion plus Noise (THD+N) of 0.003%, a minimum Signal-to-Noise Ratio of 110 dB at -12 dB attenuation, and a minimum Channel Separation of 100 dB. The device operates on a supply voltage between 4.5 V and 12 V.

Audio Special Purpose Feature Summary

• 3-wire serial interface compatible with TTL and CMOS logic levels
• Daisy-chain capability via Data-Out pin for multi-device control
• Pop and click-free attenuation transitions
• Software-customizable logarithmic attenuation curves

Audio Special Purpose Applications

• Automated studio mixing consoles
• Music reproduction systems
• Sound reinforcement systems
• Electronic music (MIDI) equipment
• Personal computer audio control

Audio Special Purpose Procurement Notes

Verify the specific ordering suffix against the Package Option Addendum. The base part number LM1972 may correspond to LIFEBUY status or require an explicit NOPB suffix for active RoHS-compliant production units. Confirm the package drawing DW matches the required 20-lead SOIC footprint and thermal characteristics before finalizing procurement.

Audio Special Purpose Selection Notes

Select this component for applications requiring precise digital volume control with high channel separation. Ensure the external circuit includes a JFET input buffer amplifier, such as the LF412, to prevent loading errors and eliminate DC pops caused by impedance changes. Verify that the system power supply remains within the 4.5 V to 12 V operating range.

Audio Special Purpose Part Context

The LM1972 belongs to the Texas Instruments μPot family of digitally controlled potentiometers. It serves as a direct replacement for legacy analog volume controls in professional audio gear. Related devices in the series include the LM1971 (62 dB single/dual channel) and LM1973 (3-channel variant), offering different attenuation ranges and channel counts for varied audio processing needs.

Audio Special Purpose Replacement Considerations

Publicly confirmed substitutes include the LM1971 and LM1973 from Texas Instruments/National Semiconductor. When replacing, verify that the pinout compatibility aligns with the 20-lead SOIC DW package. Note that the LM1973 offers three channels instead of two, while the LM1971 provides a reduced 62 dB attenuation range.

Audio Special Purpose FAQ

How is the mute function activated?

The mute function is activated by sending any binary data value of 01111111 (127) or higher (up to 11111111/255) via the serial interface. It also engages automatically upon power-up.

Why is an external buffer amplifier recommended?

An external JFET input buffer is required to maintain linearity by preventing loading of the variable output impedance and to eliminate audible clicks or pops during attenuation step changes caused by DC bias current variations in bipolar amplifiers.

What is the input impedance of the signal pins?

The AC input impedance at pins 4 and 20 is nominally 40 kΩ, with a specified range between 20 kΩ and 60 kΩ under test conditions.