Texas Instruments LP3982ILDX-ADJ

Overview

LP3982ILDX-ADJ from Texas Instruments (formerly National Semiconductor) is an adjustable-output, micropower ultra low-dropout CMOS linear regulator delivering 300mA output current with 120mV typical dropout at full load, 90µA typical quiescent current, and 37µV RMS output noise (10Hz–100kHz). It operates from 2.5V to 6.0V input and supports output voltage adjustment from 1.25V to 6.0V via external resistors - ideal for DSP core power and battery-powered portable information appliances.

For engineers reviewing the LP3982ILDX-ADJ datasheet, LP3982ILDX-ADJ pinout, LP3982ILDX-ADJ application, or LP3982ILDX-ADJ equivalent, key selection criteria include its PMOS pass transistor architecture enabling ultra-low IQ and shutdown current (1nA typ), stability with 2.2µF ceramic output capacitors, integrated FAULT detection, and thermal/overcurrent protection - all in an 8-pin LLP package.

Technical Context

The LP3982ILDX-ADJ employs a PMOS pass transistor topology with internal 1.25V bandgap reference and error amplifier, enabling true micropower operation and no-load stability. Its feedback loop incorporates an internally generated zero to ensure stability with low-ESR ceramic capacitors as small as 2.2µF.

Regulation relies on negative feedback between SET and OUT pins; the FAULT pin provides open-drain fault signaling for dropout, overcurrent, or thermal events, while SHDN enables logic-controlled 1nA shutdown mode. Input voltage range (2.5V–6.0V) and adjustable output (1.25V–6.0V) support flexible system-level power rail design.

Key Specifications

Pinout & Package

LP3982ILDX-ADJ is housed in an 8-pin LLP (Leadless Leadframe Package), measuring 3.0mm × 3.0mm × 0.8mm, with exposed thermal pad for enhanced power dissipation. The package is RoHS-compliant and optimized for high-density portable PCB layouts.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MAX8860ETD+T and TLC7703IPW, LP3982ILDX-ADJ uniquely combines adjustable output, integrated FAULT signaling, 37µV noise performance, and 1nA shutdown - making it the only option among the three qualified for precision, battery-constrained, and fault-aware portable designs.

Availability

LP3982ILDX-ADJ is available at Aetrix Electronics and suitable for wireless handsets, DSP core power, and portable information appliances requiring stable component supply, long-term lifecycle support, and RoHS-compliant packaging.

Supply support for LP3982ILDX-ADJ 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 acquired National Semiconductor in 2011 and maintains its precision analog and power management portfolio. TI is a global semiconductor leader focused on analog, embedded processing, and connectivity solutions.

The LP3982ILDX-ADJ belongs to National Semiconductor's micropower LDO family, engineered specifically for battery-powered portable electronics demanding ultra-low quiescent current, low-noise regulation, and robust fault protection in minimal footprint packages.

FAQ

What is the minimum input voltage required for LP3982ILDX-ADJ to regulate at 1.8V output?

The LP3982ILDX-ADJ requires a minimum input voltage of 2.5V per its absolute operating rating. To regulate at 1.8V output, the input must exceed 1.8V by at least the dropout voltage - 120mV typical at 300mA - so VIN ≥ 1.92V. However, since the device specification mandates VIN ≥ 2.5V regardless of VOUT, the practical minimum input remains 2.5V. This ensures proper bandgap reference and error amplifier operation across temperature and process variation. LP3982ILDX-ADJ will not function below 2.5V input, even if the theoretical dropout margin is satisfied.

How do I configure the output voltage of LP3982ILDX-ADJ using external resistors?

To configure LP3982ILDX-ADJ output voltage, connect a resistor divider between OUT (pin 3/8) and GND, with the midpoint tied to SET (pin 7). Use VO = 1.25V × (1 + R1/R2), where R2 connects from SET to GND and R1 from OUT to SET. National Semiconductor recommends R2 = 100kΩ to optimize accuracy, PSRR, and noise. For example, to set 3.3V output: R1 = 100kΩ × ((3.3/1.25) − 1) ≈ 164kΩ. The LP3982ILDX-ADJ's internal 1.25V reference and high-impedance SET pin (leakage <2.5nA) ensure precise ratio-based regulation independent of load current.

Does LP3982ILDX-ADJ require a noise bypass capacitor, and what value is optimal?

Yes, LP3982ILDX-ADJ includes a dedicated CC pin (pin 6) for a noise bypass capacitor that reduces output voltage noise. The optimal value is 33nF, using NPO or COG ceramic dielectric for minimal leakage and stable capacitance. This capacitor connects directly between pin 6 and GND. Using 33nF achieves the specified 37µV RMS noise (10Hz–100kHz); omitting it increases noise by ~2×. Larger values slow turn-on time (TON ∝ CC), while smaller values degrade noise performance. LP3982ILDX-ADJ's internal 500µA charging current ensures fast startup even with the 33nF capacitor installed.

What protection features are integrated into LP3982ILDX-ADJ?

LP3982ILDX-ADJ integrates four key protection features: (1) Thermal shutdown triggers at 160°C junction temperature with 10°C hysteresis; (2) Constant-current limiting activates at 330–770mA (typ/max) to prevent damage during short-circuit events; (3) FAULT pin asserts low during dropout, overcurrent, or thermal events - implemented as an open-drain output requiring external pull-up; (4) Reverse-battery protection is not included (unlike some competitors), so external diode or MOSFET reverse-polarity protection is recommended if input reversal is possible. All protections operate independently and are fully specified across −40°C to +85°C.

Can LP3982ILDX-ADJ operate stably with a 1µF ceramic output capacitor?

No, LP3982ILDX-ADJ is not guaranteed stable with a 1µF ceramic output capacitor. The datasheet specifies stability with ≥2.2µF ceramic capacitors (X5R/X7R dielectric, ESR <0.5Ω). Testing shows marginal phase margin and potential ringing under load transients with 1µF. While some bench setups may appear functional, production reliability requires adherence to the 2.2µF minimum. Using 1µF risks oscillation due to insufficient zero placement in the feedback loop - the internal compensation is tuned for ≥2.2µF. LP3982ILDX-ADJ's stability guarantee explicitly references 2.2µF as the minimum, and National Semiconductor validates performance only at or above this value.