Analog Devices Inc. LTC1551LCS8-4.1#TRPBF

Overview

LTC1551LCS8-4.1#TRPBF from Analog Devices (formerly Linear Technology) is a fixed-output, switched-capacitor negative voltage inverter with integrated linear post-regulator, delivering –4.1V at up to 20mA load current with <1mV_P-P output ripple, operating from 4.5V–5.25V input supply, and featuring active-high TTL-compatible shutdown - ideal for GaAs FET bias generation in portable RF transmitters.

For engineers reviewing the LTC1551LCS8-4.1#TRPBF datasheet, LTC1551LCS8-4.1#TRPBF pinout, LTC1551LCS8-4.1#TRPBF application, or LTC1551LCS8-4.1#TRPBF equivalent, key selection criteria include guaranteed ±2.5% output regulation over line/load/temperature, 900kHz charge pump frequency enabling compact 0.1µF external capacitors, low-quiescent-current shutdown (<1µA), and SO-8 package compatibility with space-constrained portable designs.

Technical Context

The LTC1551LCS8-4.1#TRPBF integrates a 900kHz inverting charge pump stage followed by a negative linear regulator using an N-channel MOSFET pass device and internal 1.225V reference. Its architecture minimizes switching artifacts via fast-loop compensation, achieving sub-millivolt ripple without requiring external LC filtering.

Unlike adjustable variants, this fixed –4.1V version uses internal resistor divider feedback and omits the ADJ pin. The active-high SHDN pin (vs. active-low on LTC1550L) simplifies interface logic in systems where high-enable control is preferred, and its internal 5µA pull-down ensures default operation without external biasing.

Key Specifications

Pinout & Package

Package: 8-lead narrow SO (S8), 0.150" body width, JEDEC MS-012AC compliant. Pin 1 marked with dot or bevel; pin numbering counterclockwise from top-left corner when viewed top-side.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LTC1550LCS8-4.1#TRPBF, the LTC1551LCS8-4.1#TRPBF simplifies system interface via built-in SHDN pull-down, while compared with LTC1551MS8-4.1#TRPBF, it retains legacy SO-8 compatibility for drop-in replacement in volume-manufactured boards.

Availability

LTC1551LCS8-4.1#TRPBF is available at Aetrix Electronics and suitable for GaAs FET bias generation, portable RF transmitter power, and single-supply instrumentation requiring stable component supply, long-term lifecycle support, and RoHS-compliant packaging.

Supply support for LTC1551LCS8-4.1#TRPBF 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, datasheet documentation, and application engineering for legacy Linear parts including the LTC series.

The LTC1550L/LTC1551L family was designed specifically for low-noise, space-constrained negative bias generation in portable RF systems - emphasizing ultra-low ripple, minimal external components, and robust regulation under dynamic load conditions.

FAQ

What is the minimum input voltage required for LTC1551LCS8-4.1#TRPBF to deliver full 20mA output current?

The LTC1551LCS8-4.1#TRPBF requires a minimum VCC of 4.75V to guarantee 20mA output current at –4.1V, as specified in the Electrical Characteristics table under "VOUT Output Regulation" for 4.75V ≤ VCC ≤ 5.25V, 0 ≤ IOUT ≤ 20mA. Below 4.75V, maximum load current decreases per the "Maximum Output Current vs Supply Voltage" curve (Figure G04).

Can LTC1551LCS8-4.1#TRPBF be used with ceramic output capacitors only, or is a tantalum/polymer capacitor required?

The LTC1551LCS8-4.1#TRPBF requires a moderate-ESR output capacitor (≥4.7µF) for loop stability - pure low-ESR ceramic-only solutions risk oscillation. A 10µF tantalum or polymer capacitor in parallel with a 0.1µF ceramic capacitor is recommended to meet both stability and <1mV_P-P ripple requirements, as confirmed in Figure F04 and Applications Information section.

How does the REG pin on LTC1551LCS8-4.1#TRPBF function, and what external components are needed?

The REG pin on LTC1551LCS8-4.1#TRPBF is an open-drain output that pulls low when VOUT is within ±5% of –4.1V. It sinks up to 4mA at 5V supply and must be externally pulled up to VCC (or up to 6V) with a resistor (typically 10kΩ–100kΩ) to generate a valid logic-high POWER VALID signal for system monitoring.

Is LTC1551LCS8-4.1#TRPBF pin-compatible with LTC1550LCS8-4.1#TRPBF, and what design changes are needed for substitution?

LTC1551LCS8-4.1#TRPBF and LTC1550LCS8-4.1#TRPBF share identical pinout and SO-8 package, but differ in SHDN polarity: LTC1551L uses active-high SHDN (internal 5µA pull-down), while LTC1550L uses active-low SHDN (requires external pull-up). Substitution requires inverting the drive signal or adding an inverter buffer - no PCB change is needed if logic level is adjusted.

What is the thermal performance of LTC1551LCS8-4.1#TRPBF in the SO-8 package under 20mA load at 5V input?

In the SO-8 (S8) package, LTC1551LCS8-4.1#TRPBF has θ_JA = 200°C/W. At 5V input and 20mA output, power dissipation is ~105mW (V_IN×I_Q + |V_OUT|×I_OUT ≈ 5V×3.65mA + 4.1V×20mA). This yields ~21°C rise above ambient - well within the 150°C T_JMAX limit even at 85°C ambient, assuming standard 2-layer PCB with copper pour.