Analog Devices Inc. LTC1551LCMS8#PBF

Overview

LTC1551LCMS8#PBF from Analog Devices (formerly Linear Technology) is a switched-capacitor regulated negative voltage inverter with integrated linear post-regulator, delivering –4.1V output at up to 20mA load current with <1mV_P-P ripple, operating from 4.5V–5.25V input supply. It features active-high TTL-compatible shutdown (SHDN), 900kHz charge pump frequency, and is optimized for GaAs FET bias generation in portable RF transmitters.

For engineers reviewing the LTC1551LCMS8#PBF datasheet, LTC1551LCMS8#PBF pinout, LTC1551LCMS8#PBF application, or LTC1551LCMS8#PBF equivalent, key selection criteria include guaranteed ±2.5% output regulation over line/load/temperature, minimal external component count (four capacitors), MSOP-8 package compatibility, and low-quiescent-current shutdown (<1µA).

Technical Context

The LTC1551LCMS8#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 load conditions.

Unlike the LTC1550L variant, the LTC1551LCMS8#PBF uses active-high shutdown logic (SHDN pulled high for normal operation), includes REG open-drain power-good indicator, and supports fixed –4.1V output without external resistors-requiring only CIN, C1, CCP, and COUT capacitors for full functionality.

Key Specifications

Pinout & Package

Package: 8-lead MSOP (MS8), 3.0mm × 3.0mm × 0.85mm body, exposed pad not electrically connected. Pin pitch: 0.65mm. RoHS-compliant, Pb-free finish (PBF).

Key Features

Applications

Equivalent & Alternatives

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

Compared with LTC1550LCMS8-4.1#PBF, LTC1551LCMS8#PBF eliminates need for external inverters in SHDN control; versus LTC1261LCS8#PBF, it delivers tighter regulation, lower noise, and integrated power-good indication-critical for RF power amplifier stability.

Availability

LTC1551LCMS8#PBF is available at Aetrix Electronics and suitable for GaAs FET bias generation, portable RF transmitter power supplies, and low-noise negative rail generation requiring stable component supply, long-term lifecycle support, and traceable sourcing.

Supply support for LTC1551LCMS8#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 continuity, technical documentation, and manufacturing for legacy Linear parts including the LTC series.

The LTC1550L/LTC1551L family was designed specifically for low-noise, capacitor-based negative voltage generation in portable RF systems-emphasizing minimal external components, ultra-low ripple, and robust regulation under dynamic loads.

FAQ

What is the minimum input voltage required for LTC1551LCMS8#PBF to regulate –4.1V output?

The LTC1551LCMS8#PBF requires a minimum VCC of 4.5V to maintain ±2.5% regulation at –4.1V output across 0–20mA load and temperature. Below 4.5V, output voltage droops nonlinearly; the datasheet guarantees performance only within 4.5V–5.25V for the –4.1V variant. This ensures compatibility with fully charged Li-ion batteries (4.2V nominal, 4.35V max) while maintaining headroom for regulation.

Can LTC1551LCMS8#PBF be used with ceramic output capacitors only?

Yes, but with strict ESR requirements: LTC1551LCMS8#PBF requires ≥10µF total output capacitance comprising a moderate-ESR bulk capacitor (e.g., 10µF tantalum or polymer) paralleled with a 0.1µF low-ESR ceramic. Using only low-ESR ceramics risks loop instability and oscillation due to missing phase-lead zero; the datasheet explicitly warns against very low ESR output capacitors alone.

Does LTC1551LCMS8#PBF require external resistors to set its output voltage?

No. The LTC1551LCMS8#PBF is the fixed –4.1V version and contains internal resistor dividers; no external resistors are needed. Only the adjustable variants (e.g., LTC1551LCMS8#PBF without suffix) require ADJ pin connections. This simplifies design, reduces BOM count, and improves production yield for dedicated –4.1V bias applications.

How does the REG pin on LTC1551LCMS8#PBF function in system design?

The REG pin on LTC1551LCMS8#PBF is an open-drain output that sinks current when VOUT is within ±5% of –4.1V. It requires an external pull-up resistor (to VCC or up to 6V) to generate a logic-high signal. This provides hardware-level power-good confirmation for sequencers or microcontrollers before enabling downstream RF circuitry, improving system reliability during power-up.

What is the thermal performance of LTC1551LCMS8#PBF in MSOP-8 package?

LTC1551LCMS8#PBF in MSOP-8 has θ_JA = 135°C/W. At 20mA load and 5V input, power dissipation is ~105mW, resulting in ~14°C junction rise above ambient. Derating is unnecessary below 85°C ambient; the device is rated for –40°C to 85°C operation with no thermal shutdown. Layout with copper pour under the exposed pad (if present) further improves thermal resistance.