Analog Devices Inc. LTC1261LCS8-4.5#PBF

Overview

LTC1261LCS8-4.5#PBF 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 output current with ±4.5% regulation accuracy, features an open-drain REG pin indicating regulation status, and operates with only three external capacitors. It is used in GaAs FET bias generation and battery-powered negative supply applications.

For engineers reviewing the LTC1261LCS8-4.5#PBF datasheet, LTC1261LCS8-4.5#PBF pinout, LTC1261LCS8-4.5#PBF application, or LTC1261LCS8-4.5#PBF equivalent, key selection criteria include fixed –4.5V output tolerance, shutdown quiescent current of 5µA, internal 650kHz oscillator frequency, SO-8 package compatibility, and REG pin logic behavior relative to output regulation window.

Technical Context

The LTC1261LCS8-4.5#PBF implements a charge-pump inverter topology with internal resistor feedback for fixed –4.5V output, regulated via cycle-by-cycle charge transfer control. Its regulation loop compares a divided replica of VOUT against a 1.23V internal reference, with a secondary 1.17V comparator enabling the REG pin when output magnitude is within 5% of setpoint.

It uses an internal 650kHz oscillator to drive MOSFET switches (S1–S4) that alternately charge and invert a 0.1µF flying capacitor. Output ripple is governed by both charge-transfer droop (e.g., ~7mV at 15mA/3.3µF) and regulation-loop bandwidth, which can be stabilized using a 100pF compensation capacitor from COMP to GND.

Key Specifications

Pinout & Package

Package: 8-lead plastic SO (Small Outline, narrow 0.150-inch body), RoHS-compliant lead-free finish, rated for 0°C to 70°C operation.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LTC1261LCS8-4#PBF, the –4V variant offers identical form-factor and regulation performance at lower output magnitude, while MAX680ESA+ provides higher output voltage at the cost of reduced switching frequency, larger external components, and incompatible pin assignment - making LTC1261LCS8-4.5#PBF optimal for precision –4.5V bias where SO-8 fit and low ripple are critical.

Availability

LTC1261LCS8-4.5#PBF is available at Aetrix Electronics and suitable for GaAs FET bias generators, portable medical sensor interfaces, and battery-powered instrumentation requiring stable component supply with guaranteed industrial-grade traceability and long-term lifecycle support.

Supply support for LTC1261LCS8-4.5#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 technical and manufacturing continuity for legacy Linear products including the LTC1261L family.

The LTC1261L series was designed specifically for compact, low-noise, capacitor-based negative voltage generation in space-constrained and battery-sensitive applications - emphasizing minimal external parts count and predictable regulation behavior without inductors.

FAQ

What is the minimum input voltage required for stable operation of the LTC1261LCS8-4.5#PBF?

The LTC1261LCS8-4.5#PBF is specified to maintain ±4.5% output regulation only when supplied with 4.75V to 5.25V. While it may oscillate and produce output below 4.75V, regulation accuracy is not guaranteed per the datasheet - design margins should enforce ≥4.75V under worst-case conditions for reliable –4.5V bias generation in the LTC1261LCS8-4.5#PBF.

Can the LTC1261LCS8-4.5#PBF be used with a 3.3V input supply?

No - the LTC1261LCS8-4.5#PBF requires a minimum 4.75V input to guarantee –4.5V output regulation. For 3.3V systems, consider the adjustable LTC1261LCS8#PBF configured for –3.3V or –2.5V output, or alternate devices like the ICL7660A. The LTC1261LCS8-4.5#PBF is not rated for 3.3V operation and will fail to regulate correctly.

What is the purpose of the COMP pin on the LTC1261LCS8-4.5#PBF, and how should it be connected?

The COMP pin on the LTC1261LCS8-4.5#PBF is internally connected to the fixed feedback divider and serves as the regulation loop compensation node. A 100pF capacitor must be connected from COMP to GND to stabilize the control loop and minimize output ripple - omitting this capacitor risks regulation "hunting" and increased ripple, especially under dynamic load. No external resistors are needed, as the LTC1261LCS8-4.5#PBF uses internal feedback.

Does the LTC1261LCS8-4.5#PBF have built-in short-circuit protection?

Yes - the LTC1261LCS8-4.5#PBF supports indefinite output short-circuit duration without damage. Its internal charge-pump switches limit peak current, and the regulation loop inherently clamps output voltage during overload. Typical short-circuit current is 100–220mA at 5.25V input, allowing safe transient fault handling without external current-limiting circuitry for the LTC1261LCS8-4.5#PBF.

How does the REG pin on the LTC1261LCS8-4.5#PBF behave during startup and under load transients?

The REG pin on the LTC1261LCS8-4.5#PBF is an open-drain output that remains high-impedance until VOUT reaches within 5% of –4.5V (i.e., –4.275V to –4.725V), then pulls low. During startup, REG stays high until regulation is achieved (~250–1500µs depending on load); under load transients, it releases high only if VOUT deviates >5% - providing robust power-valid signaling for the LTC1261LCS8-4.5#PBF without false triggers.