Texas Instruments LP3981ILD-3.3

Overview

LP3981ILD-3.3 from Texas Instruments is a micropower, ultra-low-dropout CMOS voltage regulator delivering 300 mA at fixed 3.3 V output with ≤132 mV dropout at full load, 35 µV_RMS output noise (10 Hz–100 kHz), and 60 dB PSRR at 1 kHz - optimized for battery-powered RF subsystems in cellular handsets.

For engineers reviewing the LP3981ILD-3.3 datasheet, LP3981ILD-3.3 pinout, LP3981ILD-3.3 application, or LP3981ILD-3.3 equivalent, key selection criteria include shutdown quiescent current (≤1 µA), ceramic-capacitor stability (2.2 µF min), thermal resistance (56.5°C/W in WSON), logic-controlled enable interface, and WSON-6 package compatibility with space-constrained portable designs.

Technical Context

The LP3981ILD-3.3 integrates a precision bandgap reference (1.23 V), fast-turnon circuitry, and overcurrent/thermal protection. Its low-noise architecture uses a dedicated BYPASS pin to decouple the internal reference node, enabling stable 35 µV_RMS noise without degrading transient response.

It operates across 2.7–6 V input and −40°C to +125°C junction temperature, with EN pin thresholds of V_IL ≤ 0.4 V (disable) and V_IH ≥ 1.4 V (enable), and supports output sensing via OUT-SENSE pin tied directly to OUT for accurate regulation under PCB trace impedance.

Key Specifications

Pinout & Package

LP3981ILD-3.3 is packaged in a thermally enhanced 6-pin WSON (NGC) package measuring 4.00 mm × 3.00 mm with exposed thermal pad (connected to GND). The compact footprint supports high-density portable PCB layouts while enabling 56.5°C/W junction-to-ambient thermal resistance.

Key Features

Applications

Equivalent & Alternatives

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

Compared with TPL7407LPGEDR and TPS7A0533PDQNR, LP3981ILD-3.3 uniquely delivers 300 mA output, 132 mV dropout, and 35 µV_RMS noise in WSON-6 - making it the only option among the three qualified for noise-critical, high-current RF power domains in cellular handsets.

Availability

LP3981ILD-3.3 is available at Aetrix Electronics and suitable for CDMA/GSM handset design, portable RF front-end development, and battery-powered embedded systems requiring stable component supply, consistent parametric performance, and long-term lifecycle support.

Supply support for LP3981ILD-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 was engineered specifically for battery-powered wireless handsets - prioritizing ultra-low dropout, micropower shutdown, and ultra-low-noise regulation to extend runtime and preserve RF signal fidelity.

FAQ

What is the minimum input voltage required for LP3981ILD-3.3 to maintain regulation?

The LP3981ILD-3.3 requires VIN ≥ VOUT + 0.3 V (i.e., ≥3.6 V) for guaranteed regulation per datasheet Section 8.4.1. At 300 mA load, typical dropout is 132 mV, so regulation holds down to ~3.432 V input - but below 3.6 V, output accuracy and PSRR degrade progressively. Always verify against actual load and temperature conditions using the dropout vs. temperature curves in Figure 2.

Can LP3981ILD-3.3 operate without the BYPASS capacitor?

Yes, LP3981ILD-3.3 functions without the BYPASS capacitor, delivering 3.3 V output with standard LDO performance. However, omitting the 0.033 µF capacitor increases output noise from 35 µV_RMS to ~120 µV_RMS (typical), degrading RF subsystem phase noise. The BYPASS pin is optional but strongly recommended for noise-sensitive applications like VCO or ADC supplies.

Is the OUT-SENSE pin mandatory for LP3981ILD-3.3 operation?

Yes - the OUT-SENSE pin (Pin 3) must be connected directly to the OUT pin (Pin 1) for proper regulation. This connection establishes the feedback path for the internal error amplifier. Leaving OUT-SENSE floating or connecting it elsewhere causes output voltage inaccuracy, instability, or complete failure to regulate. The datasheet explicitly states this in the Pin Descriptions table.

What is the thermal pad connection requirement for LP3981ILD-3.3 in the WSON-6 package?

The exposed thermal pad on the LP3981ILD-3.3 WSON-6 package must be soldered to a PCB copper pour connected to GND. It serves as both a thermal conduction path (reducing R_θJA to 56.5°C/W) and an electrical ground node. TI recommends a minimum 4×4 mm thermal pad with ≥4 thermal vias to an inner ground plane - failure to connect it compromises thermal performance and may trigger premature thermal shutdown under 300 mA load.

Does LP3981ILD-3.3 support ceramic output capacitors smaller than 2.2 µF?

No - the LP3981ILD-3.3 is specified and characterized for stability with 2.2 µF to 22 µF ceramic output capacitors (ESR 5–500 mΩ). Using <2.2 µF violates the minimum capacitance requirement in Section 9.2.2.4 and risks oscillation or poor transient response. For space-constrained designs, select X7R dielectric 2.2 µF 0603 or 0805 ceramics - Z5U/Y5V types are discouraged due to severe capacitance loss above 25°C.