Analog Devices Inc. LTC1550LIGN#PBF

Overview

LTC1550LIGN#PBF from Analog Devices (formerly Linear Technology) is a low-noise, switched-capacitor regulated negative voltage inverter with integrated linear post-regulator, delivering –4.1V fixed output at up to 20mA load current with <1mV_P-P ripple, operating from 4.5V–5.25V input supply, and featuring active-low TTL-compatible shutdown. It serves as a GaAs FET bias generator in portable RF transmitters and cellular handset power rails.

For engineers reviewing the LTC1550LIGN#PBF datasheet, LTC1550LIGN#PBF pinout, LTC1550LIGN#PBF application, or LTC1550LIGN#PBF equivalent, key selection criteria include guaranteed ±2.5% output regulation over line/load/temperature, 900kHz charge pump frequency minimizing IF-band interference, 0.2µA shutdown quiescent current, and compatibility with standard 0.1µF ceramic flying capacitors in space-constrained portable designs.

Technical Context

The LTC1550LIGN#PBF integrates a 900kHz inverting charge pump stage followed by a negative linear regulator with N-channel MOSFET pass device and internal 1.225V reference. Its architecture enables low dropout operation-maintaining regulation down to V_CC = 4.5V for –4.1V output-while suppressing switching artifacts via feedback loop optimization.

It uses an external resistor divider on the ADJ pin (available only in GN package) for adjustable versions, but the LTC1550LIGN#PBF is a fixed –4.1V variant in 16-lead SSOP. The REG pin provides open-drain power-good indication sinking 4mA, requiring external pull-up; PGND and AGND are separated for noise-sensitive analog regulation.

Key Specifications

Pinout & Package

Package: 16-lead narrow SSOP (GN), 5.8mm × 4.8mm, 0.635mm pitch, with exposed thermal pad (not electrically connected). Pin functions validated per Linear Technology LTC1550L/LTC1551L datasheet Rev. D.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LTC1550LCGN#PBF, LTC1550LIGN#PBF adds industrial temperature support without changing layout; versus LTC1261LCS8#PBF, it trades adjustability for lower noise, integrated regulation, and power-good signaling-critical for RF bias integrity.

Availability

LTC1550LIGN#PBF is available at Aetrix Electronics and suitable for GaAs FET biasing, portable RF power management, and single-supply analog signal conditioning requiring stable component supply and long-term lifecycle continuity.

Supply support for LTC1550LIGN#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, documentation, and manufacturing continuity for legacy Linear parts including the LTC1550L series.

The LTC1550L family was designed specifically for low-noise negative voltage generation in battery-powered RF systems, emphasizing minimal output ripple, high efficiency at light loads, and robust shutdown behavior for portable communications equipment.

FAQ

What is the minimum input voltage required for LTC1550LIGN#PBF to regulate –4.1V output?

The LTC1550LIGN#PBF requires a minimum V_CC of 4.5V to maintain –4.1V output regulation at full 20mA load, as specified in the Electrical Characteristics table. At lighter loads (≤5mA), regulation holds down to 4.2V, but design margin should preserve the 4.5V minimum to ensure ±2.5% accuracy across temperature and line variations. Below this, output voltage droops nonlinearly.

Can LTC1550LIGN#PBF be used without the REG pin connected?

Yes, the REG pin on LTC1550LIGN#PBF is optional and may be left unconnected if power-good monitoring is not required. It is an open-drain output that only sinks current when |V_OUT| is within 5% of –4.1V; no pull-up is needed unless interfacing with external logic. Leaving it floating does not affect regulation or basic functionality of the LTC1550LIGN#PBF.

Why does LTC1550LIGN#PBF require separate PGND and AGND pins?

LTC1550LIGN#PBF separates PGND (charge pump return) and AGND (regulator feedback reference) to prevent high di/dt switching currents from modulating the analog ground reference. This isolation preserves loop stability and ensures the linear regulator rejects charge pump noise effectively-key to achieving <1mV_P-P ripple. Star-grounding both to a common low-impedance plane is mandatory.

What capacitor values are mandatory for stable operation of LTC1550LIGN#PBF?

LTC1550LIGN#PBF requires four capacitors: 2.2µF ceramic at VCC (CIN), two 0.1µF ceramics for flying caps (C1+, C1– and CPOUT), and ≥10µF (tantalum or polymer) + 0.1µF ceramic at VOUT. The 10µF output cap is mandatory for <1mV_P-P ripple and loop stability; using <4.7µF risks oscillation due to insufficient phase margin in the linear regulator feedback path.

Is LTC1550LIGN#PBF pin-compatible with other LTC1550L variants in the same package?

Yes, all LTC1550L variants in the 16-lead SSOP (GN) package-including LTC1550LIGN#PBF (–4.1V fixed), LTC1550LIGN-2#PBF (–2V), and adjustable versions-share identical pinouts. The ADJ pin (Pin 12) is present but unused on fixed-output parts; REG (Pin 10) and SHDN (Pin 9) retain identical functions across the family, enabling drop-in replacement where output voltage matches system needs.