Texas Instruments LM1971N/NOPB

Overview

LM1971N/NOPB from Texas Instruments is a digitally controlled single-channel audio attenuator IC with 3-wire serial interface, 62 dB attenuation range in 1 dB steps, mute function delivering >100 dB isolation, and 0.0008% THD - used for precision volume control in PC audio, sound reinforcement, and electronic music systems.

For engineers reviewing the LM1971N/NOPB datasheet, LM1971N/NOPB pinout, LM1971N/NOPB application, or LM1971N/NOPB equivalent, key selection criteria include click-and-pop-free attenuation transitions, single-supply operation (4.5–12 V), constant 40 kΩ input impedance, logarithmic ladder architecture, and compatibility with TTL/CMOS microcontroller interfaces.

Technical Context

The LM1971N/NOPB implements a resistor ladder μPot architecture with discrete CMOS switches selecting tap points - not a variable resistor - ensuring constant input impedance but nonlinear output impedance variation across attenuation levels. Its digital control uses an 8-bit address + 8-bit data serial frame, where only address 00000000 is accepted to select the single channel.

Internal half-supply biasing at VREFIN (Pin 1) enables true single-supply AC-coupled audio operation; mute is activated by sending any data byte ≥ 00111111 (63 decimal), physically disconnecting IN from OUT and grounding OUT through ~2 kΩ. The device powers up in mute mode and requires external JFET/CMOS-input op-amp buffering to prevent linearity errors and audible DC shifts.

Key Specifications

Pinout & Package

LM1971N/NOPB is housed in an 8-pin plastic DIP (PDIP) package per JEDEC MS-001, with 0.300-inch body width, 0.100-inch lead pitch, and through-hole mounting compatibility.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar digitally controlled audio attenuator applications.

Compared with PGA2310IDW and DS1669S+, the LM1971N/NOPB uniquely combines single-supply operation, 3-wire serial control, 102 dB mute, and 0.0008% THD - making it optimal for space-constrained, microcontroller-based audio systems requiring high fidelity and silent transitions.

Availability

LM1971N/NOPB is available at Aetrix Electronics and suitable for PC audio control, sound reinforcement systems, electronic music instruments, and cellular phone audio path applications requiring stable component supply and long-term obsolescence management.

Supply support for LM1971N/NOPB includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

Texas Instruments is a global semiconductor leader specializing in analog, embedded processing, and digital signal technologies, with decades of expertise in high-performance audio and precision analog solutions.

The LM1971N/NOPB belongs to TI's Overture™ Audio Attenuator Series - designed specifically for high-fidelity, digitally controlled analog signal conditioning in professional audio, communications, and multimedia equipment.

FAQ

What is the maximum clock frequency supported by the LM1971N/NOPB serial interface?

The LM1971N/NOPB supports a maximum CLOCK frequency of 2 MHz, as specified in its Electrical Characteristics table. This allows reliable 16-bit serial data transfers within 8 µs, enabling rapid attenuation updates in real-time audio applications. Exceeding this limit risks incomplete data latching or metastability in the internal shift register of the LM1971N/NOPB.

Does the LM1971N/NOPB require external buffering at its output?

Yes, the LM1971N/NOPB requires external buffering with a high-input-impedance, low-input-bias-current op amp (e.g., JFET or CMOS type) to maintain linearity and prevent audible DC shifts. Its output impedance varies nonlinearly with attenuation setting - up to several kΩ change - and loading below 1 MΩ introduces measurable gain error and distortion in the LM1971N/NOPB signal path.

How does the mute function operate in the LM1971N/NOPB?

The LM1971N/NOPB activates mute by physically disconnecting the IN-to-OUT signal path and grounding the OUT pin through approximately 2 kΩ, achieving 102 dB typical attenuation. Mute is triggered by sending any serial data byte ≥ 00111111 (decimal 63) to the LM1971N/NOPB - including power-up default state - ensuring zero signal leakage during standby or silence.

Can the LM1971N/NOPB be used with a 3.3 V microcontroller interface?

Yes, the LM1971N/NOPB digital inputs (LOAD, DATA, CLOCK) are TTL/CMOS compatible with VIH ≥ 2.0 V and VIL ≤ 0.8 V, making them interoperable with 3.3 V logic systems without level shifters. However, VDD must still be 4.5–12 V for proper analog performance - the LM1971N/NOPB does not support 3.3 V analog supply operation.

What is the recommended method to generate the VREFIN bias voltage for the LM1971N/NOPB?

The LM1971N/NOPB VREFIN (Pin 1) must be biased at exactly VDD/2. TI recommends a simple resistor divider (two equal-value resistors from VDD to GND) plus a ≥10 µF bypass capacitor to ground for stability. For improved PSRR and lower noise, an active buffer using a dual JFET op amp (e.g., LF353) is preferred - both halves can serve VREFIN and OUT buffering in the same LM1971N/NOPB design.