Analog Devices Inc. LTC1682CMS8-3.3#PBF

Overview

LTC1682CMS8-3.3#PBF from Analog Devices (formerly Linear Technology) is a fixed-output 3.3V doubler charge pump with integrated low-noise LDO regulator, designed for powering noise-sensitive RF circuitry such as VCOs in wireless transceivers. It operates from 2.0V to 4.4V input, delivers up to 50mA output current, achieves 58µV_RMS output noise (10Hz–100kHz), and uses only ceramic capacitors-no inductors required.

For engineers reviewing the LTC1682CMS8-3.3#PBF datasheet, LTC1682CMS8-3.3#PBF pinout, LTC1682CMS8-3.3#PBF application, or LTC1682CMS8-3.3#PBF equivalent, key selection considerations include its 3.3V fixed LDO output, MSOP-8 package, 1µA shutdown current, 550kHz switching frequency, and thermal/short-circuit protection-critical for portable RF power supply design.

Technical Context

The LTC1682CMS8-3.3#PBF integrates a switched-capacitor voltage doubler and a low-dropout linear regulator in a single die. The charge pump generates ~2×VIN at CPO, which feeds the LDO stage; the LDO filters ripple and regulates precisely to 3.3V using an internal resistor divider. Its Burst Mode operation reduces quiescent current to 150µA under light load while maintaining low noise via controlled edge rates and precise 550kHz oscillator timing.

Pin 3 functions as FILT (not FB), accepting a 1nF capacitor to filter the internal 1.235V reference-directly enabling the specified 58µV_RMS noise performance. The LDO remains stable with ≥2µF ceramic output capacitance and features internal current limiting, thermal shutdown at 150°C, and a 100Ω VOUT-to-GND discharge switch during shutdown.

Key Specifications

Pinout & Package

Package: 8-Lead Plastic MSOP (3mm × 3mm, 0.65mm pitch), RoHS-compliant, moisture sensitivity level 1.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar low-noise charge-pump LDO applications.

Compared with LTC1682IMS8-3.3#PBF, the LTC1682CMS8-3.3#PBF trades extended temperature rating for lower cost and commercial-grade qualification-ideal for consumer handhelds. Versus LT1761ES5-3.3#TRPBF, it adds essential voltage boosting but with higher noise, making it uniquely suited for battery-powered RF systems needing 3.3V from sub-3.3V sources.

Availability

LTC1682CMS8-3.3#PBF is available at Aetrix Electronics and suitable for cellular transceivers, wireless PCMCIA cards, portable medical telemetry, and 2-way paging receivers requiring stable component supply with guaranteed long-term manufacturability.

Supply support for LTC1682CMS8-3.3#PBF 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

Analog Devices acquired Linear Technology in 2017 and maintains full product support, documentation, and manufacturing continuity for all Linear parts including the LTC1682 family.

The LTC1682 series was designed specifically for low-noise RF power management-targeting VCO, PLL, and mixer biasing in battery-powered wireless infrastructure and client devices where inductor-free, compact, and ultra-low-noise regulation is critical.

FAQ

What is the minimum input voltage required for reliable operation of the LTC1682CMS8-3.3#PBF?

The LTC1682CMS8-3.3#PBF requires a minimum input voltage of 2.0V for guaranteed 3.3V output regulation across temperature and load. Below 2.0V, the internal charge pump cannot generate sufficient CPO voltage to sustain LDO operation, causing dropout and increased output noise. Operation down to 1.8V is possible in some conditions but not characterized or guaranteed per datasheet specifications.

Can the LTC1682CMS8-3.3#PBF be used with input voltages above 4.4V?

No-the absolute maximum VIN rating for the LTC1682CMS8-3.3#PBF is 5.0V, but the specified operational input range is strictly 2.0V to 4.4V. Exceeding 4.4V risks violating the CPO voltage limit (max 10V) and may cause premature LDO dropout or reduced reliability. For inputs >4.4V, use an external pre-regulator or select a part like the LTC1682-5 with wider input tolerance.

Why does the LTC1682CMS8-3.3#PBF require a 1nF capacitor on the FILT pin?

The 1nF capacitor on the FILT pin (Pin 3) filters the internal 1.235V bandgap reference voltage, directly reducing high-frequency noise coupling into the LDO error amplifier. Without this capacitor, output noise increases significantly-datasheet measurements show 58µV_RMS is only achieved with the 1nF FILT cap. This is a mandatory design requirement, not optional.

How does the LTC1682CMS8-3.3#PBF behave during startup and shutdown?

At startup, the LTC1682CMS8-3.3#PBF enables the LDO only after CPO reaches ~1.75×VIN; VOUT ramps with ~2ms typical enable time. During shutdown (SHDN <0.4V), the LDO disables, CPO disconnects from VIN, and VOUT is actively discharged to GND through a 100Ω internal switch-ensuring fast, controlled de-biasing of connected RF circuitry.

Is the LTC1682CMS8-3.3#PBF pin-compatible with other variants in the LTC1682 family?

Yes-the LTC1682CMS8-3.3#PBF shares identical pinout and package (MSOP-8) with all other MS8 variants including LTC1682CMS8, LTC1682CMS8-5, LTC1682IMS8-3.3#PBF, and LTC1682IMS8-5. Pin functions are consistent across the family; only the internal feedback network (fixed 3.3V vs. adjustable or 5V) differs-allowing drop-in replacement where output voltage matches system requirements.