Analog Devices Inc. LTC1261LCMS8-4.5#PBF

Overview

LTC1261LCMS8-4.5#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 supply applications.

For engineers reviewing the LTC1261LCMS8-4.5#PBF datasheet, LTC1261LCMS8-4.5#PBF pinout, LTC1261LCMS8-4.5#PBF application, or LTC1261LCMS8-4.5#PBF equivalent, key selection criteria include fixed –4.5V output tolerance, shutdown quiescent current of 5µA, internal 650kHz oscillator frequency, MSOP-8 package compatibility, and REG pin logic behavior relative to output regulation window.

Technical Context

The LTC1261LCMS8-4.5#PBF implements a charge-pump inverter topology with internal resistor feedback for fixed –4.5V output. Its regulation loop compares a divided replica of VOUT against a 1.23V reference using COMP1, while COMP2 monitors a 1.17V threshold to assert the open-drain REG signal when output magnitude is within 5% of setpoint.

It uses an internal 650kHz oscillator to drive synchronous switching of internal MOSFETs (S1–S4), transferring charge from the 0.1µF flying capacitor to the output capacitor. The ADJ/COMP pin serves as both internal feedback node and optional ripple compensation terminal, accepting a 100pF capacitor to ground for loop stability.

Key Specifications

Pinout & Package

The LTC1261LCMS8-4.5#PBF is housed in an 8-lead plastic MSOP (MS8) package with 0.65mm pitch, 3.00mm × 3.00mm body, and exposed pad not connected internally. Thermal resistance θJA is 200°C/W.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LTC1261LCMS8-4.5#PBF, the –4V variant offers tighter voltage matching for certain GaAs devices, while the MAX680 provides higher output magnitude at lower frequency-making it suitable for less space-constrained, EMI-sensitive applications where –5V is acceptable.

Availability

LTC1261LCMS8-4.5#PBF is available at Aetrix Electronics and suitable for GaAs FET bias generators, portable sensor interfaces, and industrial signal conditioning circuits requiring stable component supply and guaranteed commercial-temperature performance.

Supply support for LTC1261LCMS8-4.5#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 its precision analog portfolio, emphasizing high-performance power management, signal conditioning, and interface ICs for industrial, automotive, and communications markets.

The LTC1261L product line was designed specifically for compact, low-noise negative voltage generation in space-constrained and battery-sensitive applications-leveraging charge-pump architecture to eliminate inductors while maintaining tight regulation.

FAQ

What is the minimum input voltage required for LTC1261LCMS8-4.5#PBF to maintain ±4.5% output regulation?

The LTC1261LCMS8-4.5#PBF requires a minimum supply voltage of 4.75V to guarantee ±4.5% regulation across its full load range (0–10mA). Below this, regulation accuracy degrades per Note 5 in the datasheet. Operation down to 4.35V is possible but not specification-guaranteed.

Can LTC1261LCMS8-4.5#PBF be used with a 3.3V input supply?

No - the LTC1261LCMS8-4.5#PBF is not rated for 3.3V operation. Its absolute minimum VCC for the –4.5V version is 4.75V. For lower input voltages, consider the adjustable LTC1261LCMS8 or other families like the LTC3260.

How does the REG pin on LTC1261LCMS8-4.5#PBF behave when the output is shorted?

When the output is shorted, VOUT collapses toward 0V, falling outside the ±5% regulation window (–4.275V to –4.725V). As a result, the REG pin remains high-impedance (not pulled low), assuming an external pull-up is present - correctly signaling loss of regulation.

Is an external capacitor required on the ADJ/COMP pin for LTC1261LCMS8-4.5#PBF?

Yes - a 100pF capacitor from ADJ/COMP (Pin 5) to GND is recommended for the LTC1261LCMS8-4.5#PBF to stabilize the regulation loop and minimize output ripple, especially under dynamic load conditions. This is explicitly shown in Figure 2 and TA07 of the datasheet.

Does LTC1261LCMS8-4.5#PBF support output currents above 20mA?

No - the LTC1261LCMS8-4.5#PBF is characterized and guaranteed for up to 20mA output current. Exceeding this may cause regulation loss, increased ripple, or thermal shutdown. For higher current, consider paralleling devices (not recommended) or selecting a different topology such as an inductive inverter.