Analog Devices Inc. LTC1261CS8-4#PBF

Overview

LTC1261CS8-4#PBF from Analog Devices (formerly Linear Technology) is a fixed-output switched-capacitor voltage inverter IC that generates a regulated –4V negative supply from a single 3V–8V positive input. It delivers up to 12mA output current with ±5% regulation, features an open-drain REG flag indicating regulation status, and operates in doubler mode using only one external 0.1µF flying capacitor-targeted for space-constrained battery-powered systems requiring clean, low-noise negative bias.

For engineers reviewing the LTC1261CS8-4#PBF datasheet, LTC1261CS8-4#PBF pinout, LTC1261CS8-4#PBF application, or LTC1261CS8-4#PBF equivalent, this page provides verified functional identity, SO-8 package mapping, confirmed –4V fixed output behavior, REG pin logic timing, shutdown current spec (5µA), and validated alternatives for regulated negative voltage generation in portable instrumentation and analog front-ends.

Technical Context

The LTC1261CS8-4#PBF implements a charge-pump-based doubler topology with internal 550kHz oscillator, fixed resistor-divider network tied to ADJ/COMP pin for –4V output, and dual-comparator regulation loop: COMP1 maintains output at 1.24V reference (referred to OUT), while COMP2 asserts REG when output reaches within 5% of setpoint. It lacks C2+ and C2– pins-unlike the 14-lead LTC1261CS-making tripler-mode operation impossible.

Its SO-8 pinout integrates GND, VCC, SHDN, REG, OUT, C1+, C1–, and ADJ/COMP (configured as COMP for fixed output). The internal reference is referenced to OUT-not ground-requiring feedback networks to be connected between OUT and ADJ/COMP, not ground. Output ripple is minimized via optional 100pF compensation capacitor from ADJ/COMP to GND.

Key Specifications

Pinout & Package

Package: 8-lead plastic SO (SO-8), 0°C to 70°C commercial temperature range, lead-free (Pb-free) finish.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MAX680ESA+ and TPS60403DBVR, the LTC1261CS8-4#PBF offers the optimal balance of fixed –4V accuracy, 5mV ripple, 600µA operating current, and SO-8 simplicity-making it ideal for cost-sensitive, noise-critical portable analog systems where design-in time and component count matter.

Availability

LTC1261CS8-4#PBF is available at Aetrix Electronics and suitable for portable instrumentation, analog front-end biasing, battery-powered audio preamps, and low-power GaAs FET biasing requiring stable component supply across volume production cycles.

Supply support for LTC1261CS8-4#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 power products.

The LTC1261 product line was designed specifically for compact, low-noise, regulated negative voltage generation in space- and power-constrained systems-emphasizing simplicity, reliability, and minimal external component count.

FAQ

What output voltage does the LTC1261CS8-4#PBF deliver, and is it adjustable?

The LTC1261CS8-4#PBF delivers a fixed –4V output with ±5% regulation tolerance across load and temperature. It is not adjustable-the internal resistor divider is factory-configured for –4V, eliminating the need for external feedback resistors. This differs from the LTC1261CS variants, which require external components for voltage setting. The LTC1261CS8-4#PBF's ADJ/COMP pin functions solely as a compensation node, not an adjustment input.

Can the LTC1261CS8-4#PBF operate from a 3.3V supply, and what is its minimum input voltage?

Yes, the LTC1261CS8-4#PBF operates from a minimum 3V input up to 8V, making it fully compatible with standard 3.3V logic rails. At 3.3V input, it sustains –4V output with up to 8mA load while maintaining regulation-verified in the Electrical Characteristics table for the –4V to –4.5V range. Below 3V, regulation degrades and the device may cease switching; 3V is the absolute minimum specified for reliable –4V operation.

How does the REG pin on the LTC1261CS8-4#PBF function, and what external circuitry is needed?

The REG pin on the LTC1261CS8-4#PBF is an open-drain output that pulls low when the magnitude of VOUT reaches ≥95% of –4V (i.e., ≤ –3.8V). It sinks up to 8mA at 5V VCC but requires an external pull-up resistor (e.g., 10kΩ to 3.3V or 5V) to assert a logic HIGH when regulation is achieved. Without the pull-up, REG remains floating and cannot signal "power good" to a microcontroller or supervisor IC.

What capacitors are required for basic operation of the LTC1261CS8-4#PBF?

The LTC1261CS8-4#PBF requires three essential capacitors: (1) a 0.1µF ceramic flying capacitor between C1+ and C1–, (2) a ≥3.3µF low-ESR output capacitor from OUT to GND (e.g., 3.3µF tantalum + 0.1µF ceramic parallel), and (3) a ≥0.1µF ceramic bypass capacitor from VCC to GND, placed adjacent to the pin. An optional 100pF capacitor from ADJ/COMP to GND reduces output ripple by stabilizing the regulation loop.

Is the LTC1261CS8-4#PBF pin-compatible with other LTC1261 variants like the LTC1261CS8 or LTC1261CS?

No-the LTC1261CS8-4#PBF is not pin-compatible with the 14-lead LTC1261CS or even the base LTC1261CS8. Its SO-8 pinout omits C2+ and C2– pins entirely and configures Pin 5 as ADJ/COMP (hardwired for –4V), whereas the adjustable LTC1261CS8 uses Pin 5 for voltage setting. Substituting packages requires PCB redesign; the LTC1261CS8-4#PBF is a purpose-built variant optimized exclusively for –4V doubler-mode operation.