Analog Devices Inc. LTC1261LCMS8#PBF

Overview

LTC1261LCMS8#PBF from Analog Devices (formerly Linear Technology) is a switched-capacitor regulated voltage inverter IC that generates a stable negative output from a single positive 2.7V–5.25V supply. It delivers up to 20mA at ±4.5% regulation, features an open-drain REG flag, 650µA typical quiescent current, and operates in an 8-pin MSOP package. It is used in GaAs FET bias generation and battery-powered systems requiring compact, low-noise negative rails.

For engineers reviewing the LTC1261LCMS8#PBF datasheet, LTC1261LCMS8#PBF pinout, LTC1261LCMS8#PBF application, or LTC1261LCMS8#PBF equivalent, key selection considerations include output regulation tolerance (±4.5%), shutdown current (5µA), ADJ/COMP pin functionality for adjustable or compensated operation, and compatibility with ceramic flying/output capacitors (0.1µF and ≥3.3µF).

Technical Context

The LTC1261LCMS8#PBF implements a 650kHz fixed-frequency charge pump with internal oscillator and feedback-controlled duty cycle modulation. Regulation is achieved by comparing a resistor-divided output voltage (at ADJ) against a 1.23V internal reference relative to VOUT - not ground - enabling precise negative-voltage control without dual supplies.

Its REG pin uses a secondary comparator (1.17V reference) to assert low when output magnitude is within 5% of setpoint, supporting power-valid signaling. Shutdown disables the pump, collapsing VOUT to 0V and reducing ICC to 5µA, while internal 5µA SHDN pull-down ensures default active operation when floating.

Key Specifications

Pinout & Package

Package: 8-lead plastic MSOP (MS8), 3.0mm × 3.0mm body, 0.65mm pitch, exposed pad optional. Thermal resistance θ_JA = 200°C/W.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MAX680ESA+ and ICL7660AIBAZ, the LTC1261LCMS8#PBF uniquely combines adjustable output, ±4.5% regulation, REG flag, and MSOP packaging - making it optimal for precision GaAs biasing and battery-sensitive designs where both accuracy and status monitoring matter.

Availability

LTC1261LCMS8#PBF 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, guaranteed industrial-grade traceability, and long-term lifecycle support.

Supply support for LTC1261LCMS8#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 its legacy of high-performance analog ICs, especially in power management and precision signal conditioning.

The LTC1261LCMS8#PBF belongs to Linear's switched-capacitor voltage converter family, designed specifically for compact, inductor-free negative rail generation in space-constrained and low-noise applications such as RF biasing and portable instrumentation.

FAQ

What is the function of the ADJ pin on the LTC1261LCMS8#PBF?

The ADJ pin on the LTC1261LCMS8#PBF serves as the feedback input for output voltage regulation. It accepts a resistor-divider voltage referenced to VOUT (not ground), comparing it to an internal 1.23V reference. For the LTC1261LCMS8#PBF - the adjustable version - this allows setting output voltages from –1.23V to –5V. The pin draws only ±0.01µA bias current, minimizing divider error. In fixed-output variants like LTC1261LCMS8-4#PBF, the divider is internal and ADJ becomes COMP for optional ripple compensation.

Can the LTC1261LCMS8#PBF operate from a 3.3V supply?

Yes, the LTC1261LCMS8#PBF is fully specified to operate from 2.7V to 5.25V, including standard 3.3V rails. At 3.3V input, it can deliver regulated outputs down to –1.5V (per electrical characteristics table, VOUT = –1.448V to –1.552V at 0–10mA). Output current capability scales with input voltage - e.g., maximum 20mA is guaranteed above 3.85V VCC for –3V output. Performance remains within ±4.5% regulation across the full commercial temperature range (0°C to 70°C).

How does the REG pin on the LTC1261LCMS8#PBF indicate regulation status?

The REG pin on the LTC1261LCMS8#PBF is an open-drain output that pulls low when the magnitude of VOUT is within 5% of its setpoint (e.g., –4.75V to –5.25V for a –5V target). It sinks ≥5mA at 5V VCC and tolerates pull-up voltages up to 6V. Critically, REG asserts only when VOUT is *below* the setpoint - it stays high if VOUT is forced *above* (e.g., –4.2V for a –5V target). This behavior makes it ideal for power-valid sequencing but requires external pull-up for logic-level interfacing. The LTC1261LCMS8#PBF's REG function is implemented via a dedicated 1.17V comparator referenced to the same internal bandgap.

What external capacitors are required for basic operation of the LTC1261LCMS8#PBF?

The LTC1261LCMS8#PBF requires three mandatory external capacitors: a 0.1µF ceramic flying capacitor between C1+ and C1–, a ≥1µF ceramic input bypass capacitor from VCC to GND, and a ≥3.3µF ceramic output capacitor from OUT to GND. An optional 100pF compensation capacitor from ADJ to GND reduces output ripple by stabilizing the regulation loop. All ceramics must be X7R or better; tantalum or aluminum electrolytics require parallel 0.1µF ceramics to suppress high-frequency spikes that disrupt regulation. These values are validated in the LTC1261LCMS8#PBF's typical applications and performance curves.

Is the LTC1261LCMS8#PBF pin-compatible with other members of the LTC1261L family?

Yes, all LTC1261L variants - including LTC1261LCMS8#PBF (adjustable), LTC1261LCMS8-4#PBF (–4V fixed), and LTC1261LCMS8-4.5#PBF (–4.5V fixed) - share identical 8-pin MSOP pinouts and thermal characteristics. Pin functions (VCC, C1+, C1–, GND, ADJ/COMP, OUT, REG, SHDN) are electrically and physically identical. The only differences are internal resistor networks (for fixed versions) and minor specification limits (e.g., minimum VCC). This allows direct substitution in existing layouts when changing output voltage requirements - provided external components (e.g., ADJ resistors vs. COMP cap) are updated accordingly.