Texas Instruments LP3981IMMX-2.5/NOPB

Overview

LP3981IMMX-2.5/NOPB from Texas Instruments is a micropower, ultra-low-dropout CMOS voltage regulator delivering 300 mA at fixed 2.5 V output, with 132 mV typical dropout at full load, ≤1 µA shutdown current, and 35 µV_RMS output noise (10 Hz–100 kHz). It serves as the primary power supply for RF front-end ICs and baseband processors in battery-powered cellular handsets.

For engineers reviewing the LP3981IMMX-2.5/NOPB datasheet, LP3981IMMX-2.5/NOPB pinout, LP3981IMMX-2.5/NOPB application, or LP3981IMMX-2.5/NOPB equivalent, key selection criteria include dropout performance under 300-mA load, PSRR >60 dB at 1 kHz, ceramic-capacitor stability, thermal resistance in WSON-6, and enable-controlled shutdown leakage <1.5 µA across −40°C to +125°C.

Technical Context

The LP3981IMMX-2.5/NOPB employs a CMOS pass element with internal 1.23-V bandgap reference and fast-turnon circuitry, enabling 240 µs typical startup time. Its feedback loop uses OUT-SENSE for remote sensing, supporting accurate regulation despite PCB trace IR drop.

It integrates thermal shutdown (160°C trip), short-circuit current limiting (600 mA), and logic-level EN control with VIH = 1.4 V and VIL = 0.4 V. The BYPASS pin connects to a 0.033-µF capacitor to reduce reference noise without degrading transient response.

Key Specifications

Pinout & Package

LP3981IMMX-2.5/NOPB is packaged in a thermally enhanced 6-pin WSON (NGC) package measuring 4.00 mm × 3.00 mm with exposed thermal pad (pin 4 = GND). This package delivers R_θJA = 56.5°C/W, enabling 1.77 W power dissipation at T_A = 25°C.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar LDO regulator applications.

Compared with TPL7407LPGQ and MCP1703T-2502E/MB, LP3981IMMX-2.5/NOPB uniquely combines ultra-low noise (35 µV_RMS), remote sensing (OUT-SENSE), and sub-µA shutdown-making it irreplaceable for RF and high-fidelity analog power domains where spectral purity and regulation accuracy are non-negotiable.

Availability

LP3981IMMX-2.5/NOPB is available at Aetrix Electronics and suitable for CDMA/WCDMA handset design, portable medical sensors, and industrial handheld terminals requiring stable component supply, long-term lifecycle support, and guaranteed traceability.

Supply support for LP3981IMMX-2.5/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 company headquartered in Dallas, Texas, specializing in analog, embedded processing, and wireless connectivity solutions for industrial, automotive, and consumer markets.

The LP3981 family was engineered specifically for battery-powered wireless infrastructure and mobile terminals, emphasizing micropower operation, ultra-low noise, and ceramic-capacitor compatibility to reduce bill-of-materials and PCB area.

FAQ

What is the maximum input voltage rating for LP3981IMMX-2.5/NOPB?

The absolute maximum input voltage for LP3981IMMX-2.5/NOPB is 6.5 V, but recommended operating conditions specify VIN ≤ 6 V. Exceeding 6 V risks permanent damage per Absolute Maximum Ratings. For reliable operation across temperature, maintain VIN between 2.7 V and 6 V - this range ensures 2.5-V output regulation while preserving 132-mV dropout margin at full 300-mA load. Always use a 2.2-µF input capacitor rated for ≥10 V.

Does LP3981IMMX-2.5/NOPB require an external bypass capacitor for basic operation?

No, LP3981IMMX-2.5/NOPB operates fully functional without the BYPASS capacitor. However, connecting a 0.033-µF ceramic capacitor from BYPASS (Pin 5) to GND reduces output noise from ~120 µV_RMS to 35 µV_RMS (10 Hz–100 kHz) by filtering the internal bandgap reference. This is critical for RF and audio applications but optional for digital-only loads. The capacitor must be low-leakage (e.g., C0G/NPO ceramic) to avoid output voltage error.

How does the OUT-SENSE pin function in LP3981IMMX-2.5/NOPB?

The OUT-SENSE pin (Pin 3) provides remote voltage sensing for improved regulation accuracy. In standard configuration, it must be shorted to OUT (Pin 1) on the PCB. When routed separately to the load's power entry point, it compensates for voltage drop across PCB traces - maintaining ±3% output accuracy even with 100-mΩ trace resistance at 300 mA. This feature is essential for high-precision analog supplies where local regulation at the LDO output is insufficient.

What thermal performance can be expected from LP3981IMMX-2.5/NOPB in its WSON-6 package?

LP3981IMMX-2.5/NOPB in the NGC (WSON-6) package achieves R_θJA = 56.5°C/W under JEDEC High-K board conditions. With T_J(MAX) = 125°C and T_A = 25°C, this allows 1.77 W of power dissipation - sufficient for 300 mA at 2.5-V output with up to 3.5-V input (ΔV = 1.0 V → P_D = 0.3 W). Real-world performance depends on PCB copper area under the thermal pad; doubling the pad size typically improves R_θJA by 15–20%.

Is LP3981IMMX-2.5/NOPB stable with 2.2 µF ceramic output capacitors?

Yes, LP3981IMMX-2.5/NOPB is explicitly designed and characterized for stability with 2.2 µF ceramic output capacitors (X7R, Y5V, or Z5U dielectrics) having ESR between 5 mΩ and 500 mΩ. This eliminates the need for larger, higher-ESR tantalum capacitors. TI confirms stability across temperature and load transients in the datasheet Figure 12 (Line Transient Response) and Section 9.2.2.4. For best results, place C_OUT within 5 mm of OUT and GND pins.