Analog Devices Inc. LTC1261LIS8-4.5#PBF

Overview

LTC1261LIS8-4.5#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 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 LTC1261LIS8-4.5#PBF datasheet, LTC1261LIS8-4.5#PBF pinout, LTC1261LIS8-4.5#PBF application, or LTC1261LIS8-4.5#PBF equivalent, key selection criteria include its fixed –4.5V output, industrial temperature range (–40°C to +85°C), MSOP-8 package, shutdown quiescent current of 5µA, and REG pin functionality for power-valid signaling.

Technical Context

The LTC1261LIS8-4.5#PBF implements a 650kHz internal oscillator-driven inverting charge pump topology. Regulation is achieved via a precision 1.23V internal reference compared against a resistor-divided replica of the output at the ADJ/COMP pin - internally connected for fixed-output variants. Output voltage stability relies on feedback loop bandwidth control using an optional 100pF compensation capacitor from COMP to GND.

Its REG output is an open-drain N-channel transistor that sinks ≥5mA at VCC = 5V when |VOUT| is within 5% of the setpoint (i.e., –4.275V ≤ VOUT ≤ –4.5V). Shutdown is activated by pulling SHDN high, disabling the charge pump and collapsing VOUT to 0V while reducing ICC to 5µA typical.

Key Specifications

Pinout & Package

Package: 8-Lead Plastic SO (S8), 0.150-inch narrow body, RoHS-compliant lead-free finish (PBF).

Key Features

Applications

Equivalent & Alternatives

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

Compared with LTC1261LCS8-4.5#PBF, the LTC1261LIS8-4.5#PBF offers extended temperature operation essential for industrial deployments; versus LTC1261LIMS8-4.5#PBF, it provides lower thermal resistance (θJA = 135°C/W) enabling higher sustained output current in SO-8 form factor.

Availability

LTC1261LIS8-4.5#PBF is available at Aetrix Electronics and suitable for GaAs FET bias generators, battery-powered sensor interfaces, and single-supply op-amp negative rail applications requiring stable component supply and long-term industrial-grade availability.

Supply support for LTC1261LIS8-4.5#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 product support, datasheets, and application engineering for legacy Linear parts including the LTC1261L series.

The LTC1261L belongs to Linear's precision switched-capacitor DC/DC converter family, designed specifically for low-noise, low-component-count negative rail generation in RF, portable, and industrial analog systems.

FAQ

What is the minimum input voltage required for stable operation of the LTC1261LIS8-4.5#PBF?

The LTC1261LIS8-4.5#PBF requires a minimum supply voltage of 4.75V to guarantee ±4.5% output regulation at full load. While it may function below this threshold, the datasheet explicitly states that output accuracy is not assured outside the 4.75V–5.25V range. This makes the LTC1261LIS8-4.5#PBF ideal for 5V systems with tight tolerance margins but unsuitable for 3.3V or wide-input-range applications.

Can the LTC1261LIS8-4.5#PBF be used without the optional COMP capacitor?

Yes, the LTC1261LIS8-4.5#PBF operates correctly without the optional 100pF capacitor from COMP (Pin 5) to GND. That capacitor is recommended only to reduce output voltage ripple under heavy or dynamic loads. In static, low-current applications (e.g., GaAs FET bias at <5mA), the LTC1261LIS8-4.5#PBF achieves acceptable ripple (<10mV) with just the required 0.1µF flying and 3.3µF output capacitors.

How does the REG pin on the LTC1261LIS8-4.5#PBF indicate regulation status?

The REG pin on the LTC1261LIS8-4.5#PBF is an open-drain output that pulls low (≤0.8V at 5mA sink) when the magnitude of VOUT is within 5% of –4.5V (i.e., –4.275V ≤ VOUT ≤ –4.5V). It remains high-impedance otherwise and requires an external pull-up resistor (typically 10kΩ to 5V) to generate a logic-high signal. This provides unambiguous power-valid feedback without additional components.

Is the LTC1261LIS8-4.5#PBF pin-compatible with other variants in the LTC1261L family?

Yes, all LTC1261L variants-including LTC1261LIS8-4.5#PBF, LTC1261LIS8-4#PBF, and LTC1261LIS8#PBF-share identical SO-8 pinouts and package dimensions. The only functional differences are internal resistor network configurations for output voltage setting; no PCB changes are needed when substituting between fixed-output versions in the same package and temperature grade.

What is the maximum continuous output current supported by the LTC1261LIS8-4.5#PBF at 85°C ambient?

At TA = 85°C, the LTC1261LIS8-4.5#PBF supports up to 20mA continuous output current when mounted on a standard FR-4 PCB with adequate copper pour. Its SO-8 package has θJA = 135°C/W, so with 5.25V input and 20mA load, junction temperature rise is ~18°C above ambient - well within the 150°C absolute maximum. Derating is not required for this condition per the datasheet's thermal specifications.