Texas Instruments LP3981IMMX-3.3

Overview

LP3981IMMX-3.3 from Texas Instruments is a micropower, ultra-low-dropout CMOS voltage regulator delivering 3.3 V at up to 300 mA from a 2.5–6 V input, 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 rail for RF front-end ICs and baseband processors in cellular handsets.

For engineers reviewing the LP3981IMMX-3.3 datasheet, LP3981IMMX-3.3 pinout, LP3981IMMX-3.3 application, or LP3981IMMX-3.3 equivalent, key selection criteria include dropout performance under 200–300 mA loads, ceramic-capacitor stability with 2.2 µF C_OUT, EN logic threshold compatibility (V_IL ≤ 0.4 V, V_IH ≥ 1.4 V), and thermal resistance in WSON-6 (R_θJA = 56.5 °C/W).

Technical Context

The LP3981IMMX-3.3 employs a PMOS pass transistor architecture enabling ultra-low dropout and minimal ground current increase in dropout-critical for battery runtime extension. Its internal bandgap reference (1.23 V) feeds a precision error amplifier that regulates via OUT-SENSE feedback, supporting remote sensing for improved load regulation.

It integrates fast-turnon circuitry (240 µs typical t_ON with 0.033 µF BYPASS capacitor), thermal shutdown (160 °C), and short-circuit current limiting (600 mA). The BYPASS pin connects to a high-impedance node in the reference circuit, allowing external 0.033 µF capacitor placement to reduce output noise without degrading transient response.

Key Specifications

Pinout & Package

LP3981IMMX-3.3 is packaged in a thermally enhanced 6-pin WSON (NGC) package (4.00 mm × 3.00 mm) with exposed thermal pad connected to GND.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LP3981IMMX-3.3, TPL7407LPGEDR trades noise performance for lower cost and simpler layout, while MCP1703T-3302E/MB offers deeper shutdown current but sacrifices output current and dropout-making LP3981IMMX-3.3 optimal for 300-mA, low-noise, battery-constrained RF power rails.

Availability

LP3981IMMX-3.3 is available at Aetrix Electronics and suitable for CDMA handset power management, WCDMA baseband supply, and portable information appliance core regulation requiring stable component supply across production lifecycles.

Supply support for LP3981IMMX-3.3 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 designing analog ICs, embedded processors, and system solutions for industrial, automotive, and communications markets.

The LP3981 family targets battery-powered wireless infrastructure and mobile terminals, emphasizing ultra-low dropout, micropower shutdown, and ceramic-capacitor compatibility to reduce bill-of-materials and PCB area.

FAQ

What is the maximum input voltage rating for LP3981IMMX-3.3?

The absolute maximum input voltage for LP3981IMMX-3.3 is 6.5 V. However, the recommended operating range is 2.7 V to 6 V per the datasheet's Recommended Operating Conditions table. Exceeding 6.5 V risks permanent damage; operation above 6 V may degrade long-term reliability even if within absolute max limits. LP3981IMMX-3.3 must maintain at least 0.3 V headroom above 3.3 V (i.e., VIN ≥ 3.6 V) for guaranteed regulation.

Can LP3981IMMX-3.3 operate stably with a 1-µF ceramic output capacitor?

No-LP3981IMMX-3.3 requires a minimum 2.2 µF ceramic output capacitor for guaranteed stability, as specified in Section 9.2.2.4 of the datasheet. Using 1 µF violates the design requirement and may cause oscillation or poor transient response. The device supports 2.2–22 µF ceramic capacitors with 5–500 mΩ ESR; X7R dielectric is recommended for temperature stability.

Does LP3981IMMX-3.3 require the OUT-SENSE pin to be connected externally?

Yes-LP3981IMMX-3.3 requires OUT-SENSE (Pin 3) to be shorted directly to OUT (Pin 1) on the PCB. This connection is mandatory for proper regulation, as stated in the Pin Descriptions table: "Must be connected to OUT for proper operation." Leaving OUT-SENSE floating or unconnected will result in incorrect output voltage and potential instability.

What is the thermal resistance of LP3981IMMX-3.3 in its WSON-6 package?

LP3981IMMX-3.3 in the NGC (WSON-6) package has a junction-to-ambient thermal resistance (R_θJA) of 56.5 °C/W under JEDEC JESD51-7 High-K test conditions. Its junction-to-board resistance (R_θJB) is 30.9 °C/W. These values assume proper PCB layout with the exposed thermal pad soldered to a solid copper ground plane-failure to implement this reduces thermal performance significantly.

Is the BYPASS pin on LP3981IMMX-3.3 optional or mandatory for basic operation?

The BYPASS pin on LP3981IMMX-3.3 is optional for basic regulation but mandatory to achieve the specified 35 µV_RMS output noise. Without the 0.033 µF capacitor connected from BYPASS to GND, output noise rises significantly. The pin must not be left floating-it should either connect to the capacitor or be tied directly to GND if noise performance is not required, though TI does not characterize that configuration.