Analog Devices Inc. LT1171CT#06PBF

Overview

LT1171CT#06PBF from Analog Devices (formerly Linear Technology) is a monolithic 2.5A high-efficiency current-mode switching regulator IC in TO-220-5 package, supporting buck, boost, flyback, inverting, and Cuk topologies. It operates from 3V to 60V input, delivers up to 50W output power, integrates a 2.5A/65V internal switch, and features 100kHz fixed-frequency operation with 6mA quiescent current - used in industrial DC-DC conversion where wide VIN range and topology flexibility are required.

For engineers reviewing the LT1171CT#06PBF datasheet, LT1171CT#06PBF pinout, LT1171CT#06PBF application, or LT1171CT#06PBF equivalent, key selection criteria include verified 2.5A switch current limit (TJ ≥ 25°C), flyback-regulated floating output capability, adaptive anti-saturation drive, shutdown mode drawing only 50µA, and compatibility with standard 5-pin TO-220 thermal layout practices.

Technical Context

The LT1171CT#06PBF implements current-mode control with a 100kHz oscillator, enabling fast line/load transient response and simplified loop compensation. Its internal 2.5A/65V NPN power switch uses adaptive anti-saturation drive to maintain efficiency across wide load ranges without external sensing resistors.

It supports dual regulation modes: normal feedback (1.24V reference at FB pin) and isolated flyback mode (15V flyback reference), selectable via FB pin voltage threshold (0.45V). The VC pin serves as error amplifier output, current limit adjust, soft-start node, and shutdown control - pulled below 0.15V for 50µA standby.

Key Specifications

Pinout & Package

LT1171CT#06PBF is housed in a 5-lead plastic TO-220 package (T package) with tab connected to GND. Thermal resistance θJA = 75°C/W enables operation up to 100°C ambient without forced airflow when mounted on ≥2.8 in² copper area.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar switching regulator applications.

Compared with LT1170CT#PBF and LT1172CT#PBF, the LT1171CT#06PBF delivers optimal balance of output current (2.5A), thermal performance (θJA = 75°C/W), and board-area efficiency - making it the preferred choice for mid-power industrial and battery systems requiring robust, topology-flexible regulation without over-engineering.

Availability

LT1171CT#06PBF is available at Aetrix Electronics and suitable for industrial DC-DC conversion, battery-powered upconversion, and floating isolated supply applications requiring stable component supply, long-term lifecycle support, and traceable sourcing.

Supply support for LT1171CT#06PBF 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 the LT117x family.

The LT117x series was designed as monolithic high-power switching regulators targeting applications needing wide-input-voltage operation, topology flexibility, and integrated protection - especially where discrete controller+FET solutions increase cost and complexity.

FAQ

What is the maximum continuous output power achievable with the LT1171CT#06PBF?

The LT1171CT#06PBF supports up to 50W continuous output power in standard buck or boost configurations when properly heatsinked. This assumes 2.5A switch current limit, 65V breakdown margin, and thermal design maintaining junction temperature ≤100°C. Derating applies above 60°C ambient or with inadequate copper area - consult AN19 for efficiency calculations and thermal modeling specific to LT1171CT#06PBF.

Does the LT1171CT#06PBF support flyback topology with transformer isolation?

Yes, the LT1171CT#06PBF supports flyback-regulated mode via its dedicated flyback amplifier. When the FB pin voltage drops below 0.45V, it switches to regulating the flyback pulse amplitude relative to VIN, enabling fully floating outputs without optocouplers. The 15V flyback reference voltage (±1.3V) and built-in blanking time ensure stable regulation - confirmed in LT1170/LT1171/LT1172 datasheet Figure TA03 and Section "Operation".

What is the function of the VC pin on the LT1171CT#06PBF, and how is it used for current limiting?

The VC pin on the LT1171CT#06PBF is the error amplifier output and serves four functions: frequency compensation, current limit adjustment, soft-start control, and shutdown activation. For current limiting, externally clamping VC between 1.0V and 2.0V linearly scales peak switch current from 0A to 2.5A - e.g., 1.5V on VC yields ~1.25A limit. This is implemented using a diode clamp or op-amp circuit per Application Note 19, ensuring precise, adjustable overload protection without additional components.

Can the LT1171CT#06PBF be synchronized to an external clock?

Yes, the LT1171CT#06PBF supports external synchronization in the 120kHz–160kHz range by pulling the VC pin to ground with a narrow (<0.3µs) pulse via an external transistor. This enables EMI reduction through frequency dithering or multi-phase interleaving. The datasheet specifies that synchronizing pulses must not disturb VC's DC operating point - C2 (39pF) and R1/R2 network ensure correct pulse width and amplitude, as shown in Figures OP01 and OP02.

What thermal considerations apply to the LT1171CT#06PBF in TO-220 package?

The LT1171CT#06PBF in TO-220 package has θJA = 75°C/W. To maintain TJ ≤100°C, ambient temperature must be limited based on dissipation: e.g., at 2.5A/12V output (30W), assuming 85% efficiency, PD ≈ 5.3W → ΔT = 398°C - thus mandatory heatsinking is required. With 2.8 in² copper, θJA improves to ~45°C/W; actual layout must follow Linear's recommended pad pattern and thermal vias. Thermal foldback activates above TJ ≈ 125°C, but sustained operation above 100°C requires derating per datasheet curves.