Analog Devices Inc. LTC1147CS8-3.3#PBF

Overview

LTC1147CS8-3.3#PBF from Analog Devices (formerly Linear Technology) is a high-efficiency, constant off-time current-mode step-down switching regulator controller driving an external P-channel MOSFET to deliver a fixed 3.3V output. It operates from 3.5V to 16V input, achieves >95% efficiency at full load, maintains regulation down to 160µA quiescent current in Burst Mode, and supports 100% duty cycle for ultra-low dropout operation - ideal for battery-powered portable instruments and GPS systems.

For engineers reviewing the LTC1147CS8-3.3#PBF datasheet, LTC1147CS8-3.3#PBF pinout, LTC1147CS8-3.3#PBF application, or LTC1147CS8-3.3#PBF equivalent, key selection considerations include its 3.3V fixed output, 8-pin SOIC package, 125mV current sense threshold range, 5µs typical off-time, and compatibility with logic-level shutdown control - all critical for low-voltage, high-efficiency DC/DC converter design.

Technical Context

The LTC1147CS8-3.3#PBF implements a constant off-time current-mode architecture that sets switching frequency via external CT capacitor and dynamically adjusts off-time discharge current as VIN approaches VOUT to suppress audible noise and maintain stability near dropout. Its internal voltage divider on SENSE– (Pin 4) fixes the regulated output at 3.3V with ±3% accuracy over temperature and line/load conditions.

Burst Mode operation engages automatically below ~15mA load to reduce IQ to 160µA, while the SHDN pin (Pin 6) enables micropower shutdown with <20µA supply current. The device integrates short-circuit protection, 100% duty cycle capability, and a built-in 25mV–150mV adjustable current sense threshold window referenced to VOUT.

Key Specifications

Pinout & Package

8-pin plastic SOIC (S8) package with θJA = 150°C/W; exposed pad not present. Pin 7 (GND) requires separate high-current return paths to COUT(–) and diode cathode.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar step-down controller applications.

Compared with LTC1147IS8-3.3, the LTC1147CS8-3.3 trades extended temperature rating for lower cost and identical performance in commercial environments; versus TPS54202DRCT, it offers superior light-load efficiency and dropout behavior but requires external FET and diode - making it optimal for high-reliability, low-power, fixed-output applications.

Availability

LTC1147CS8-3.3#PBF is available at Aetrix Electronics and suitable for portable medical sensors, notebook subsystem power, GPS tracking modules, and industrial handheld scanners requiring stable component supply with guaranteed long-term manufacturability.

Supply support for LTC1147CS8-3.3#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, datasheets, and application notes for the LTC portfolio.

The LTC1147 series was designed specifically for high-efficiency, low-quiescent-current step-down regulation in battery-powered and energy-sensitive systems - emphasizing Burst Mode operation, wide input range, and robust current-mode control.

FAQ

What is the regulated output voltage tolerance of the LTC1147CS8-3.3#PBF?

The LTC1147CS8-3.3#PBF delivers a fixed 3.3V output with ±3% initial accuracy (3.23V to 3.43V) at 700mA load and 25°C. Over the full 0°C to 70°C commercial temperature range and 3.5V–16V input, total variation remains within ±5%, verified per Electrical Characteristics table in the official datasheet.

Can the LTC1147CS8-3.3#PBF operate with input voltage as low as 3.5V?

Yes - the LTC1147CS8-3.3#PBF is explicitly rated for VIN down to 3.5V (per Absolute Maximum Ratings and Note 5), enabling use with single-cell Li-ion batteries at end-of-discharge. At this minimum input, it maintains regulation via 100% duty cycle operation, delivering VOUT ≈ VIN − ILOAD × RDS(ON) of the external P-MOSFET.

How does Burst Mode operation affect efficiency at light loads for the LTC1147CS8-3.3#PBF?

Burst Mode reduces switching activity below ~15mA load, cutting IQ from 1.6mA to 160µA and maintaining >85% efficiency down to zero load. This avoids the steep efficiency drop seen in forced continuous mode, extending battery life significantly in intermittently active devices like GPS trackers and wireless sensors using the LTC1147CS8-3.3#PBF.

What is the recommended RSENSE value for 2A maximum output current with the LTC1147CS8-3.3#PBF?

For IMAX = 2A, the datasheet recommends RSENSE = 100mV / IMAX = 0.05Ω (per Figure 2 and Application Information). This yields a current sense threshold window of 25mV–150mV, ensuring reliable peak-current limiting and Burst Mode entry at ~15mA while supporting full 2A continuous output with appropriate MOSFET and inductor sizing.

Does the LTC1147CS8-3.3#PBF require external compensation components?

No - the LTC1147CS8-3.3#PBF uses a constant off-time current-mode architecture that is inherently stable and does not require external loop compensation. The reference design in Figure 1 (with CT = 470pF, L = 50µH, RSENSE = 0.05Ω) provides adequate stability across line, load, and temperature for most applications using the LTC1147CS8-3.3#PBF.