Analog Devices Inc. LTC1261LCMS8-4#TRPBF

Overview

LTC1261LCMS8-4#TRPBF from Analog Devices (formerly Linear Technology) is a fixed-output switched-capacitor voltage inverter IC that generates a regulated –4V output from a single 4.35V to 5.25V positive supply. It delivers up to 20mA output current with ±4.5% regulation accuracy, features an open-drain REG flag indicating regulation status, and operates with only three external capacitors. It is used in GaAs FET bias generation and battery-powered negative rail applications.

For engineers reviewing the LTC1261LCMS8-4#TRPBF datasheet, LTC1261LCMS8-4#TRPBF pinout, LTC1261LCMS8-4#TRPBF application, or LTC1261LCMS8-4#TRPBF equivalent, key selection criteria include guaranteed –4V output regulation across temperature, 650kHz internal oscillator frequency, shutdown quiescent current of 5µA, MSOP-8 package compatibility, and REG pin behavior for power-valid signaling in compact portable systems.

Technical Context

The LTC1261LCMS8-4#TRPBF implements a charge-pump inverter architecture with internal 1.23V reference and dual comparators: COMP1 regulates output by dynamically truncating 650kHz clock pulses based on feedback at the ADJ/COMP pin, while COMP2 (1.17V threshold) drives the open-drain REG output when VOUT is within 5% of –4V. The device uses internal resistor division for fixed –4V output, eliminating external feedback resistors.

It requires no inductor and achieves regulation via cycle-by-cycle charge transfer control. Input-to-output voltage relationship is constrained by absolute maximum ratings: total VCC-to-VOUT differential must not exceed 10.8V, and output must remain ≥ –5.3V. Output short-circuit current is rated at 100–220mA, enabling robust fault tolerance without external current limiting.

Key Specifications

Pinout & Package

Package: 8-lead plastic MSOP (MS8), 3.00mm × 3.00mm × 0.86mm body, 0.65mm pitch, exposed pad not electrically connected.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar switched-capacitor voltage inverter applications.

Compared with MAX680ESA+ and TPS60403DBVR, the LTC1261LCMS8-4#TRPBF offers unique integration of precise –4V regulation, built-in REG flag, and optimized 650kHz operation for minimal capacitor footprint - making it ideal for space-constrained GaAs bias and portable instrumentation where deterministic power-valid signaling is essential.

Availability

LTC1261LCMS8-4#TRPBF is available at Aetrix Electronics and suitable for GaAs FET bias generators, portable medical sensors, and industrial PLC I/O modules requiring stable component supply with lead-free compliance and tape-and-reel packaging.

Supply support for LTC1261LCMS8-4#TRPBF 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 its precision analog and power management portfolio with rigorous testing and long-term product support.

The LTC1261L series was designed specifically for compact, low-noise negative rail generation in RF and portable applications - emphasizing regulation accuracy, minimal external components, and reliable power-good signaling without inductors.

FAQ

What is the minimum input voltage required for LTC1261LCMS8-4#TRPBF to maintain regulated –4V output?

The LTC1261LCMS8-4#TRPBF requires a minimum supply voltage of 4.35V to guarantee ±4.5% output regulation across temperature and load. Operation below this voltage may yield unregulated output or failure to start; the datasheet explicitly states that specifications are not assured below 4.35V, even though the device may function.

Can LTC1261LCMS8-4#TRPBF be used with a 3.3V input supply?

No - the LTC1261LCMS8-4#TRPBF is not specified for 3.3V operation. Its minimum VCC is 4.35V, and attempting to operate at 3.3V will result in undervoltage lockout or unregulated output. For 3.3V-compatible inverters, consider the adjustable LTC1261LCMS8 or other families like the LTC3260.

How does the REG pin on LTC1261LCMS8-4#TRPBF behave under load transients?

The REG pin on LTC1261LCMS8-4#TRPBF remains low only when |VOUT| is within 5% of –4V (i.e., –3.8V to –4.2V). During fast load steps, if VOUT temporarily droops below –3.8V or overshoots above –4.2V, REG goes high (open-drain released), providing real-time indication of regulation loss - useful for fault logging or dynamic power management.

Is an external compensation capacitor required for stable operation of LTC1261LCMS8-4#TRPBF?

An external 100pF capacitor from COMP (Pin 5) to GND is optional but recommended to reduce output ripple, especially under heavy loads or with high-ESR output capacitors. The datasheet confirms this capacitor improves regulation loop bandwidth and prevents comparator "hunting" that increases ripple beyond specification.

What is the thermal performance of LTC1261LCMS8-4#TRPBF in MSOP-8 package at 20mA load?

In the MSOP-8 package, LTC1261LCMS8-4#TRPBF has θJA = 200°C/W. At 20mA output into –4V with 5V input, power dissipation is ~20mW, resulting in <5°C junction rise above ambient - well within the 150°C TJMAX limit and suitable for unrestrained operation in standard FR4 PCB layouts without heatsinking.