LM4871MX/NOPB: Complete Guide to TI's 3W Mono Class-AB Audio Amplifier (Specs, Pinout, Alternatives)

The LM4871MX/NOPB is a mono bridged (BTL) Class-AB audio power amplifier from Texas Instruments, part of the Boomer series. It delivers 3W continuous average power into a 3Ω load at 10% THD from a 5V supply (1.5W into 8Ω), operates from a 2V to 5.5V supply, and comes in an 8-pin SOIC (D) surface-mount package rated from -40°C to 85°C. A shutdown mode cuts current draw to just 0.7µA typical, making it ideal for battery-powered audio designs. The part is active in lifecycle, RoHS compliant, lead-free (NOPB), and in stock at XAIPART with 99,999 units — pricing starts at $0.42 per unit at 1,000 pieces as of 2026-09-04 ($0.85 for single units). Its differential (bridged) output eliminates output coupling capacitors, reducing board space and external component count.

What Is the LM4871MX/NOPB and Why Do Engineers Choose It?

The LM4871MX/NOPB is a single-channel audio power amplifier that amplifies low-power analog audio signals to a level suitable for driving loudspeakers directly. Texas Instruments classifies it in the Boomer series of audio amplifiers, and it is a Class-AB design — a topology that offers a good compromise between efficiency and linearity, providing low distortion while consuming moderate power.

The defining architectural feature is the bridged-tied load (BTL) configuration. In a BTL output, the speaker is driven differentially by two out-of-phase outputs (VOUT+ and VOUT-), which effectively doubles the voltage swing across the load compared with a single-ended amplifier. This maximizes output power without increasing supply voltage, and it eliminates the need for large output coupling capacitors — saving board area and improving low-frequency response.

Key verified specifications at a glance:

Parameter | Value
Output Power | 3W into 3Ω at 5V, 10% THD (1.5W into 8Ω at 10% THD)
Supply Voltage Range | 2V to 5.5V
Quiescent Current | 6.5mA typical
Shutdown Current | 0.7µA typical
Amplifier Type | Class-AB, Mono (1 channel)
Load Impedance (min) | 3Ω
THD+N | 10% max at rated power
Operating Temperature | -40°C to 85°C
Package / Mounting | SOIC-8 (D), Surface Mount
RoHS / Lead-Free | Compliant / Yes (NOPB)

Full details are in the official TI datasheet: LM4871 datasheet (PDF).

How Do You Design In the LM4871MX/NOPB? A Practical Technical Guide

Power Supply Considerations

The 2V to 5.5V supply range is the LM4871's superpower for portable design. It accepts a single-cell Li-ion battery across most of its discharge curve, three AA/AAA cells, or a regulated 5V rail. To get the full 3W into 3Ω, plan for a 5V supply; at lower battery voltages, output power scales down. Place a decoupling capacitor close to the VDD pin (pin 6) and maintain a solid ground plane to minimize noise and improve thermal performance, as the datasheet guidance recommends.

Understanding the Pinout

The SOIC-8 pinout is straightforward:

Pin | Name | Function
1 | SHUTDOWN | Shutdown control input, active low
2 | BYPASS | Bypass capacitor connection
3 | VOUT- | Negative (bridged) output
4 | GND | Ground
5 | VOUT+ | Positive (bridged) output
6 | VDD | Power supply
7 | VIN- | Inverting input
8 | VIN+ | Non-inverting input

The SHUTDOWN pin (pin 1, active low) is your primary power-management lever: pulling it low drops supply current from 6.5mA to 0.7µA typical — roughly a 9,000x reduction — which is transformative for battery life in devices that spend most of their time idle.

Gain Setting and Speaker Connection

Connect your speaker directly across VOUT+ (pin 5) and VOUT- (pin 3). Because the output is differential/bridged, no DC-blocking coupling capacitor is required, which simplifies the BOM and improves low-frequency response. Set the gain with input and feedback resistors around VIN+ (pin 8) and VIN- (pin 7); consult the application circuits in the TI datasheet for recommended gain-network values. The BYPASS pin (pin 2) requires a bypass capacitor to stabilize the internal reference and improve power-supply rejection [VERIFY_NEEDED: recommended bypass capacitor value from datasheet].

Thermal and Layout Best Practices

At full 3W output into 3Ω, a Class-AB amplifier dissipates significant heat. The device includes internal thermal shutdown protection as a safety net, but good design avoids relying on it: provide adequate copper area around the SOIC-8 package, keep the ground plane continuous under the part, and ensure airflow in enclosed products like laptops or GPS units. The verified operating range of -40°C to 85°C covers typical consumer and industrial ambient conditions.

What Are the Main Application Scenarios?

Verified applications from the product database include:

Portable speakers: 3W into 3Ω from 5V, with 6.5mA quiescent and 0.7µA shutdown currents extending battery life; the 2V-5.5V range supports single-cell Li-ion.

Mobile phones: Loudspeaker amplification for ringtones and media, with differential output driving the speaker without DC blocking capacitors.

MP3 players: Clean audio to headphones or small speakers with minimal external components for compact designs.

Laptop speakers: Up to 3W into 3Ω from a readily available 5V rail; thermal shutdown protects in confined spaces.

GPS navigation devices: Clear voice prompts with low idle power via the shutdown pin.

Toys and handheld gaming devices: Low cost, small size, and thermal robustness suit high-volume consumer products.

What Are the Best Alternatives and Drop-In Replacements for the LM4871MX/NOPB?

According to verified XAIPART data, the alternatives are:

Alternative | Relationship to LM4871MX/NOPB | Drop-In?
LM4871M/NOPB | Same die, supplied in a tube instead of tape and reel | Yes — pin-compatible, functionally identical
LM4871MM/NOPB | Same electrical function in a VSSOP-8 package instead of SOIC-8 | No — different footprint
LM4991 | Higher output power (3.1W into 3Ω), similar pinout | Mostly — verify parameters [VERIFY_NEEDED: full spec comparison]
TPA2011D1 | Class-D amplifier, higher efficiency, pin-compatible | Pin-compatible; output class differs — verify EMI/filtering needs
SSM2211SZ | Cross-brand (Analog Devices) mono Class-AB amp in SOIC-8, similar specs; TI lists LM4871 as an alternative on its E2E forum | Verify pin compatibility and electrical specs before substituting

Practical guidance: If you need a true drop-in, choose LM4871M/NOPB — identical silicon, only packaging (tube vs. tape and reel) differs. If your priority is efficiency and battery runtime, the pin-compatible TPA2011D1 Class-D may fit better, but Class-D introduces different EMI and filtering considerations. If you need slightly more output power, LM4991 delivers 3.1W into 3Ω. For a swap from ADI's SSM2211SZ, the LM4871 is listed by TI as an alternative, but always check datasheets for exact pinout parity before layout.

What Is the Market Position, Lifecycle Status, and Supply Situation?

The LM4871MX/NOPB is listed as active in lifecycle status. Supply is healthy: XAIPART currently stocks 99,999 units with MOQ of 1, priced at $0.42/unit at 1,000 pieces as of 2026-09-04. Tiered pricing verified as of 2026-09-04: $0.85 (qty ≥1), $0.75 (qty ≥10), $0.60 (qty ≥100), $0.50 (qty ≥500), and $0.42 (qty ≥1000). Distributor snapshots from 2026-08-25 show LCSC listing the part at $0.3689 with 14,463 units in stock, with DigiKey and Mouser also carrying it — indicating broad multi-channel availability for production planners.

What Should Buyers Watch? Trends and Outlook

Class-D migration: TI's own pin-compatible TPA2011D1 offers higher efficiency in the same footprint. For new battery-powered designs where runtime dominates, evaluate Class-D; the LM4871's Class-AB linearity and simplicity remain strong where EMI-sensitive analog layouts or lowest BOM cost matter most.

Battery-voltage flexibility: The verified 2V-5.5V range keeps the LM4871 relevant as single-cell Li-ion designs push toward lower cutoff voltages — but remember output power is maximized at 5V (3W into 3Ω).

Purchasing strategy: The price step from $0.60 (100 pcs) to $0.42 (1,000 pcs) as of 2026-09-04 is a 30% saving — plan reel-level buys via the tape-and-reel LM4871MX/NOPB rather than tube packaging for automated assembly.

Lifecycle confidence: With active status and six-figure stock at XAIPART, supply risk is low for current designs; still, for multi-year programs, confirm longevity expectations with TI directly [VERIFY_NEEDED: TI longevity commitment for LM4871].

Key Takeaways for Design Engineers

The LM4871MX/NOPB remains a workhorse choice for cost-sensitive, battery-powered mono audio: 3W into 3Ω at 5V, a forgiving 2V-5.5V supply range, a 0.7µA shutdown mode for aggressive power management, and a bridged output that eliminates coupling capacitors. With SOIC-8 packaging, -40°C to 85°C operation, active lifecycle status, and sub-$0.50 pricing at volume as of 2026-09-04, it is easy to source and easy to design in. Check the LM4871MX/NOPB product page on XAIPART for real-time stock, or browse Amplifier ICs and Texas Instruments components for alternatives.