Analog Devices Inc. LTC1261LIMS8-4.5#TRPBF

Overview

LTC1261LIMS8-4.5#TRPBF from Analog Devices (formerly Linear Technology) is a fixed-output switched-capacitor voltage inverter IC that generates a regulated –4.5V output from a single 4.75V to 5.25V positive supply. It delivers up to 20mA load current with ±4.5% output regulation, 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 systems requiring compact negative rail synthesis.

For engineers reviewing the LTC1261LIMS8-4.5#TRPBF datasheet, LTC1261LIMS8-4.5#TRPBF pinout, LTC1261LIMS8-4.5#TRPBF application, or LTC1261LIMS8-4.5#TRPBF equivalent, key selection criteria include guaranteed –4.5V output at 5mA under industrial temperature range (–40°C to +85°C), MSOP-8 package compatibility, shutdown quiescent current of 5µA, and REG pin functionality for power-valid signaling.

Technical Context

The LTC1261LIMS8-4.5#TRPBF implements a 650kHz internal oscillator-driven charge pump topology to invert and regulate input voltage. Its feedback loop compares a divided replica of VOUT against an internal 1.23V reference via the ADJ/COMP pin, enabling precise output control without external resistors for fixed versions.

Regulation is achieved by dynamically truncating clock pulses to the charge pump based on real-time output error detection. The REG pin uses a secondary comparator referenced to 1.17V (5% below VREF) to assert low when |VOUT| is within 5% of the setpoint - e.g., –4.275V to –4.5V for the –4.5V variant - providing system-level power-good indication.

Key Specifications

Pinout & Package

Package: 8-lead plastic MSOP (MS8), 3.00mm × 3.00mm body, 0.65mm pitch, –40°C to +85°C industrial temperature grade.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LTC1261LIMS8-4.5#TRPBF, the –4V variant offers identical form-factor and thermal behavior but targets different bias points, while the MAX680 provides tighter regulation at the cost of missing the REG pin and slower switching - impacting filter size and transient response.

Availability

LTC1261LIMS8-4.5#TRPBF is available at Aetrix Electronics and suitable for GaAs FET bias generators, battery-powered instrumentation, and single-supply signal conditioning circuits requiring stable component supply and industrial-grade reliability.

Supply support for LTC1261LIMS8-4.5#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 portfolio, emphasizing high-performance power management, signal conditioning, and interface ICs for demanding industrial and communications applications.

The LTC1261L series was designed specifically for compact, low-noise negative rail generation in space-constrained systems - prioritizing minimal external components, robust regulation under variable load, and integrated power-status signaling.

FAQ

What is the minimum input voltage required for LTC1261LIMS8-4.5#TRPBF to maintain ±4.5% output regulation?

The LTC1261LIMS8-4.5#TRPBF requires a minimum supply voltage of 4.75V to guarantee ±4.5% output regulation across its full industrial temperature range (–40°C to +85°C) and load conditions up to 5mA. Below this voltage, regulation performance is not specified per the datasheet, though operation may continue with degraded accuracy.

Does LTC1261LIMS8-4.5#TRPBF require external resistors to set its output voltage?

No, the LTC1261LIMS8-4.5#TRPBF does not require external resistors. Its –4.5V output is factory-trimmed and internally configured using a fixed resistor divider connected to the ADJ/COMP pin. This eliminates tuning components and ensures consistent output across units and temperature.

How does the REG pin on LTC1261LIMS8-4.5#TRPBF function, and what external circuitry is needed?

The REG pin on LTC1261LIMS8-4.5#TRPBF is an open-drain output that pulls low when |VOUT| is within 5% of –4.5V (i.e., –4.275V to –4.5V). It requires an external pull-up resistor to a logic-compatible voltage (up to 6V). With a 5V pull-up, it sinks ≥5mA, enabling direct interfacing with microcontroller GPIO or power-management ICs.

Can LTC1261LIMS8-4.5#TRPBF operate with ceramic output capacitors only, or is a tantalum capacitor required?

The LTC1261LIMS8-4.5#TRPBF works optimally with low-ESR ceramic output capacitors (e.g., 3.3µF X7R). Tantalum is not required and may degrade regulation if ESR exceeds ~1Ω. For best performance, use a 3.3µF ceramic capacitor - optionally paralleled with a 0.1µF ceramic cap - to suppress high-frequency spikes and ensure stable feedback loop behavior.

What is the typical startup time for LTC1261LIMS8-4.5#TRPBF under full load?

The typical startup time for LTC1261LIMS8-4.5#TRPBF is 250µs when VCC = 5V and IOUT = 5mA, reaching –4.5V within regulation tolerance. This value is consistent across the LTC1261L-4 and LTC1261L-4.5 variants and is independent of output capacitor value, as regulation engages immediately after initial charge transfer cycles.