Analog Devices Inc. LTC1551CS8-4.1#PBF

Overview

LTC1551CS8-4.1#PBF from Analog Devices (formerly Linear Technology) is a fixed-output, switched-capacitor voltage inverter IC with integrated linear post-regulator, generating a regulated –4.1V output from a single 4.5V–6.5V positive supply. It delivers up to 10mA load current, maintains ±5% output regulation, achieves <1mV_P-P output ripple, and features an active-high TTL-compatible shutdown pin. It is used as a low-noise GaAs FET bias generator in portable RF transmitters.

For engineers reviewing the LTC1551CS8-4.1#PBF datasheet, LTC1551CS8-4.1#PBF pinout, LTC1551CS8-4.1#PBF application, or LTC1551CS8-4.1#PBF equivalent, key selection criteria include its fixed –4.1V output, 900kHz charge pump frequency, SO-8 package, shutdown quiescent current <1µA, and compatibility with 0.1µF external charge pump capacitors.

Technical Context

The LTC1551CS8-4.1#PBF integrates a 900kHz switched-capacitor inverting charge pump followed by a negative linear regulator using an N-channel MOSFET pass device and internal 1.24V reference. Its feedback loop monitors VOUT via the SENSE pin to maintain tight regulation despite load and line variations.

Unlike the adjustable LTC1550CGN, the LTC1551CS8-4.1#PBF uses internal resistor dividers to fix the output at –4.1V and employs an active-high SHDN pin-distinct from the LTC1550's active-low control-enabling direct interface with microcontroller GPIOs without inversion logic.

Key Specifications

Pinout & Package

Package: 8-lead plastic SO (SO-8, narrow 0.150"), JEDEC MS-012, thermal resistance θ_JA = 150°C/W.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LTC1550CS8-4.1#PBF, the LTC1551CS8-4.1#PBF offers identical regulation and noise performance but simplifies control interface via active-high SHDN; compared with LTC1261CS8-5#PBF, it provides superior output accuracy, lower ripple, and higher current capability at the cost of fixed –4.1V output.

Availability

LTC1551CS8-4.1#PBF is available at Aetrix Electronics and suitable for portable RF transmitters, GaAs FET bias circuits, and battery-powered instrumentation requiring stable component supply, low-noise negative voltage generation, and long-term lifecycle support.

Supply support for LTC1551CS8-4.1#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) is a global leader in high-performance analog, mixed-signal, and digital signal processing semiconductors, serving industrial, automotive, communications, and healthcare markets.

The LTC1550/LTC1551 family was designed specifically for low-noise, space-constrained GaAs FET bias generation in portable RF systems - emphasizing ultra-low ripple, minimal external component count, and robust regulation under varying battery conditions.

FAQ

What is the function of the SENSE pin on the LTC1551CS8-4.1#PBF?

The SENSE pin on the LTC1551CS8-4.1#PBF is the feedback input for the internal linear regulator, connected directly to the VOUT pin near the load to compensate for PCB trace voltage drop. This ensures accurate –4.1V regulation at the point of use, not just at the IC pin. For optimal performance, SENSE must be routed with minimal impedance and avoid sharing traces with high-current paths. The LTC1551CS8-4.1#PBF relies on this connection to maintain ±5% output accuracy across temperature and load variations.

Can the LTC1551CS8-4.1#PBF operate from a 3.3V supply?

No, the LTC1551CS8-4.1#PBF requires a minimum supply voltage of 4.5V per its Absolute Maximum Ratings and Electrical Characteristics table. Operation below 4.5V is not guaranteed and may result in loss of regulation, reduced output current, or failure to start. For 3.3V-input applications, consider the LTC1550CGN (adjustable version, 2.7V–6.5V range) or alternative charge pumps like the LTC3260. The LTC1551CS8-4.1#PBF is specifically optimized for 4.5V–6.5V inputs, such as 5V logic rails or partially discharged Li-ion batteries.

What is the purpose of the 0.1µF capacitor on the CPOUT pin of the LTC1551CS8-4.1#PBF?

The 0.1µF capacitor on the CPOUT pin of the LTC1551CS8-4.1#PBF serves as the charge storage capacitor for the internal switched-capacitor inverter stage, stabilizing the negative voltage delivered to the linear regulator's input. It works in conjunction with the C1+/C1– flying capacitors to transfer charge at 900kHz. Using a low-ESR ceramic capacitor here minimizes high-frequency losses and ensures efficient energy transfer. Omitting or undersizing this capacitor causes excessive CPOUT ripple, degrading the linear regulator's ability to suppress noise - directly impacting the LTC1551CS8-4.1#PBF's <1mV_P-P output specification.

How does the shutdown behavior differ between LTC1551CS8-4.1#PBF and LTC1550CS8-4.1#PBF?

The LTC1551CS8-4.1#PBF features an active-high shutdown pin (SHDN), meaning it enters ultra-low-power mode (<1µA supply current) when SHDN is pulled to VCC, and resumes operation when SHDN is pulled low. In contrast, the LTC1550CS8-4.1#PBF uses an active-low SHDN pin - shutdown is asserted by pulling the pin to GND. This polarity difference means the two parts are not pin-compatible replacements without modifying the control logic or adding an inverter. Both achieve identical regulation and ripple performance, but the LTC1551CS8-4.1#PBF simplifies interface with standard GPIOs that default high or drive high-active signals.

What output capacitor configuration is required to achieve <1mV_P-P ripple with the LTC1551CS8-4.1#PBF?

To achieve <1mV_P-P output ripple with the LTC1551CS8-4.1#PBF, the datasheet specifies a minimum 10µF output capacitor (e.g., tantalum or polymer) in parallel with an additional 0.1µF ceramic capacitor placed close to the VOUT and GND pins. The 10µF capacitor handles bulk energy storage and low-frequency ripple, while the 0.1µF ceramic shunts high-frequency switching spikes generated by the 900kHz charge pump. Using only the 10µF capacitor yields significantly higher ripple (>5mV_P-P); the ceramic capacitor is essential to suppress sharp harmonics and meet the LTC1551CS8-4.1#PBF's specified noise performance.