Texas Instruments LP3985IM5-3.1/NOPB

Overview

LP3985IM5-3.1/NOPB from Texas Instruments is a micropower, ultra-low-noise, 150mA CMOS low-dropout (LDO) voltage regulator in a 5-pin SOT-23 package, delivering a fixed 3.1V output with ≤100mV dropout at full load, 30µVrms output noise (10Hz–100kHz), and 200µs typical turn-on time. It serves as a precision power supply for RF front-ends, baseband processors, and analog sensor circuits in space-constrained portable wireless devices.

For engineers reviewing the LP3985IM5-3.1/NOPB datasheet, LP3985IM5-3.1/NOPB pinout, LP3985IM5-3.1/NOPB application, or LP3985IM5-3.1/NOPB equivalent, key selection criteria include its 1.5µA shutdown quiescent current, ceramic-capacitor stability (1µF min), logic-controlled enable input, thermal/short-circuit protection, and −40°C to +125°C operating junction temperature range.

Technical Context

The LP3985IM5-3.1/NOPB employs a CMOS pass transistor architecture with a bandgap reference (1.23V nominal) and internal fast-turn-on circuit that pre-charges the BYPASS pin capacitor via a 70µA current source. Its feedback loop is optimized for stability with 1µF ±30% ceramic output capacitors and supports optional 0.01µF noise-reduction capacitance without degrading load transient response.

It features a logic-compatible enable input (VIH = 1.4V min, VIL = 0.4V max), thermal shutdown activation at 160°C with 20°C hysteresis, and short-circuit current limiting at 600mA (steady-state). Dropout voltage remains linearly controlled up to 150mA load, with ground current increasing only marginally in dropout-extending battery runtime in portable systems.

Key Specifications

Pinout & Package

The LP3985IM5-3.1/NOPB uses the industry-standard 5-pin SOT-23 (DBV) package, measuring 2.9mm × 1.6mm × 1.15mm, with gull-wing leads and RoHS-compliant matte tin (CuSn) finish. It is rated MSL Level-1 (unlimited floor life at <30°C/85% RH).

Key Features

Applications

Equivalent & Alternatives

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

Compared with TPL720F31 and MCP1700T-3102E/TT, the LP3985IM5-3.1/NOPB offers optimal balance of ultra-low noise, micropower shutdown, and integrated enable functionality in a standard 5-pin SOT-23 footprint-making it ideal for battery-powered RF and precision analog subsystems requiring both performance and controllability.

Availability

LP3985IM5-3.1/NOPB is available at Aetrix Electronics and suitable for CDMA/GSM handset design, portable medical instrumentation, IoT edge node development, and RF module manufacturing requiring stable component supply across long production lifecycles.

Supply support for LP3985IM5-3.1/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 leader specializing in analog, embedded processing, and digital signal technologies, with decades of expertise in power management ICs for high-reliability applications.

The LP3985 series was designed specifically for portable wireless systems demanding ultra-low noise, micropower operation, and minimal PCB footprint-targeting cellular handsets, portable information appliances, and battery-powered RF subsystems.

FAQ

What is the maximum input voltage rating for the LP3985IM5-3.1/NOPB?

The LP3985IM5-3.1/NOPB has an absolute maximum input voltage (VIN) rating of 6.5V, with recommended operating range from 2.5V to 6.0V. Exceeding 6.5V may cause permanent damage. For reliable operation in battery-powered designs, VIN should remain within 2.5V–6.0V, especially when paired with Li-ion (4.2V max) or dual-alkaline (3.2V typical) sources.

Does the LP3985IM5-3.1/NOPB require a minimum load current to maintain regulation?

No, the LP3985IM5-3.1/NOPB remains stable and in regulation with zero load current-a feature explicitly confirmed in the datasheet under "NO-LOAD STABILITY." This makes LP3985IM5-3.1/NOPB suitable for RTC backup rails, CMOS RAM keep-alive, and other always-on, ultra-low-current applications without requiring dummy loads.

Can the BYPASS pin of the LP3985IM5-3.1/NOPB be left unconnected?

Yes, the BYPASS pin of the LP3985IM5-3.1/NOPB may be left floating or unconnected without affecting basic regulation. However, omitting the 0.01µF NPO/COG capacitor forfeits the 30µVrms noise specification-the device reverts to ~230nV/√Hz noise density, increasing broadband output noise significantly. For RF or precision analog use, the capacitor is mandatory.

What is the thermal shutdown behavior of the LP3985IM5-3.1/NOPB?

The LP3985IM5-3.1/NOPB activates thermal shutdown at 160°C junction temperature with 20°C hysteresis, meaning it resumes normal operation only after cooling to ≤140°C. During shutdown, VOUT drops to near-zero while quiescent current remains at ≤1.5µA. This protects against sustained overload or poor heatsinking in compact enclosures.

Is the LP3985IM5-3.1/NOPB compatible with 1µF X5R ceramic output capacitors?

Yes, the LP3985IM5-3.1/NOPB is stable with 1µF X5R ceramic output capacitors, though X7R is preferred for full −40°C to +125°C operation due to superior temperature coefficient (±15% vs. ±15% over narrower −55°C to +85°C for X5R). X5R remains acceptable in commercial-temperature applications where ambient stays below 85°C.