Analog Devices Inc. LTC1550LCMS8-2#PBF

Overview

LTC1550LCMS8-2#PBF from Analog Devices (formerly Linear Technology) is a fixed-output, low-noise switched-capacitor voltage inverter with integrated linear post-regulator, delivering –2V at up to 20mA with ±2.5% regulation over line, load, and temperature. It operates from a single 2.7V–5.25V supply, features 900kHz charge pump frequency, <1mV_P-P output ripple, and TTL-compatible active-low shutdown. It is optimized for GaAs FET bias generation in portable RF transmitters.

For engineers reviewing the LTC1550LCMS8-2#PBF datasheet, LTC1550LCMS8-2#PBF pinout, LTC1550LCMS8-2#PBF application, or LTC1550LCMS8-2#PBF equivalent, key selection criteria include guaranteed –2V output regulation across 0–20mA load, 0.2µA shutdown current, MSOP-8 package compatibility, and minimal external component count (four capacitors only).

Technical Context

The LTC1550LCMS8-2#PBF 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 feedback loop is optimized for fast transient response to suppress switching artifacts from CPOUT, enabling stable regulation under dynamic GaAs FET bias loads.

It employs star-ground layout requirements for VCC bypass, CPOUT, and VOUT capacitors to minimize noise coupling. The REG pin provides open-drain power-valid indication (sinking 4mA), while SHDN is active-low and requires external pull-up for default operation - distinct from the LTC1551L's active-high variant.

Key Specifications

Pinout & Package

Package: 8-lead MSOP (MS8), 3.0mm × 3.0mm × 0.85mm body, exposed pad not connected, RoHS-compliant #PBF finish.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LTC1550LCMS8-2#PBF, the –2.5V variant shifts bias point for higher-V_th FETs but raises minimum input voltage, while the LTC1261L trades ripple performance for flexibility and lower cost - neither offers identical –2V/low-ripple capability without redesign.

Availability

LTC1550LCMS8-2#PBF is available at Aetrix Electronics and suitable for portable RF transmitters, battery-powered instrumentation, and single-supply signal conditioning requiring stable component supply, guaranteed long-term availability, and traceable sourcing.

Supply support for LTC1550LCMS8-2#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, known for high-performance power management and signal conditioning ICs.

The LTC1550L family was designed specifically for low-noise, compact negative bias generation in portable RF systems - prioritizing ripple suppression, small footprint, and minimal external components over general-purpose DC/DC conversion.

FAQ

What is the minimum input voltage required for LTC1550LCMS8-2#PBF to deliver 20mA at –2V?

The LTC1550LCMS8-2#PBF requires a minimum VCC of 3.75V to guarantee 20mA output current at –2V, as specified in the Electrical Characteristics table under "VOUT Output Regulation" for the LTC1550L-2 variant. Below this voltage, maximum load current decreases progressively - e.g., 10mA is supported down to 3.1V, and 5mA down to 2.7V.

Does LTC1550LCMS8-2#PBF require an external resistor on the SHDN pin?

Yes, the LTC1550LCMS8-2#PBF SHDN pin is active-low and has no internal pull-up. An external pull-up resistor (typically 100kΩ to VCC) is required to ensure normal operation at power-on; otherwise, the device remains in shutdown. This differs from the LTC1551L, which includes an internal pull-down.

Can LTC1550LCMS8-2#PBF be used with ceramic output capacitors only?

No - the LTC1550LCMS8-2#PBF requires a moderate-ESR output capacitor (e.g., tantalum or polymer) of ≥4.7µF for loop stability. A low-ESR ceramic capacitor alone will cause oscillation. However, a 0.1µF ceramic capacitor must be placed in parallel with the main output capacitor to suppress high-frequency spikes.

What is the function of the REG pin on LTC1550LCMS8-2#PBF?

The REG pin on LTC1550LCMS8-2#PBF is an open-drain output that pulls low when the –2V output is within ±5% of regulation. It sinks up to 4mA and requires an external pull-up resistor (to VCC or another logic rail) to generate a valid high-level signal. It serves as a power-good indicator for system sequencing.

Is LTC1550LCMS8-2#PBF compatible with the LTC1551L pinout?

Yes - the LTC1550LCMS8-2#PBF and LTC1551L share identical MSOP-8 pinouts and package dimensions. However, their SHDN logic is inverted (active-low vs. active-high), so direct substitution requires verifying control-signal polarity and updating any associated pull-up/pull-down network.