Analog Devices Inc. LT1171IQ#TRPBF

Overview

LT1171IQ#TRPBF from Analog Devices (formerly Linear Technology) is a monolithic 2.5A high-efficiency current-mode switching regulator IC in a 5-lead plastic TO-220 package, operating from 3V to 60V input, delivering up to 50W output power in buck/boost/flyback topologies, with 100kHz fixed-frequency switching, 6mA quiescent current, and internal switch saturation voltage of 0.5Ω typical - used in industrial DC-DC conversion where wide VIN range and rugged topology flexibility are required.

For engineers reviewing the LT1171IQ#TRPBF datasheet, LT1171IQ#TRPBF pinout, LT1171IQ#TRPBF application, or LT1171IQ#TRPBF equivalent, this page provides verified functional identity, confirmed thermal and electrical specs per commercial-grade (-40°C to 100°C) operation, validated pin roles for TO-220 package, real-world flyback and boost use cases, and two rigorously cross-checked alternative parts with documented parameter divergence.

Technical Context

The LT1171IQ#TRPBF implements current-mode control with adaptive anti-saturation drive for the integrated 2.5A NPN switch, enabling stable regulation across wide load and line variations without external compensation complexity. Its error amplifier delivers 3000–7000 µmho transconductance and features dual-mode feedback: normal 1.24V reference for direct-output regulation and programmable flyback mode (15.0–18.0V reference) for isolated transformer-coupled designs.

It supports shutdown via VC pin (≤0.15V threshold), drawing only 50µA in standby, and includes internal 2.3V low-dropout bias regulator, 100kHz oscillator, and built-in overcurrent protection with duty-cycle-dependent current limit (2.5A at 50% DC, down to 2.0A at 80% DC). The TO-220 package provides θ_JA = 75°C/W and θ_JC = 4°C/W for thermally constrained industrial environments.

Key Specifications

Pinout & Package

LT1171IQ#TRPBF uses a 5-lead plastic TO-220 package (T package) with tab connected to GND. Thermal resistance is θ_JA = 75°C/W and θ_JC = 4°C/W, enabling operation up to 100°C ambient without heatsink in moderate-power designs.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar high-current monolithic switching regulator applications.

Compared with LM2596T-ADJ and LT3757AEDD, the LT1171IQ#TRPBF uniquely combines 2.5A integrated bipolar switching, flyback-mode capability, and VC-pin controllability in a thermally robust TO-220 package - making it optimal for ruggedized 30–50W industrial supplies where simplicity, isolation, and transient resilience are prioritized over ultra-high efficiency or miniaturization.

Availability

LT1171IQ#TRPBF is available at Aetrix Electronics and suitable for industrial automation, battery-powered instrumentation, and isolated communications power supplies requiring stable component supply, long-term lifecycle support, and guaranteed traceable sourcing.

Supply support for LT1171IQ#TRPBF 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 legacy Linear switching regulators.

The LT1170/LT1171/LT1172 family was designed for high-reliability, wide-input-voltage DC-DC conversion in industrial, transportation, and telecom infrastructure - emphasizing topology flexibility, ruggedness, and minimal external component count over ultra-high frequency or digital control.

FAQ

What is the maximum continuous output power achievable with the LT1171IQ#TRPBF in boost configuration?

The LT1171IQ#TRPBF supports up to 50W continuous output power in boost mode under typical conditions (e.g., 12V input to 24V output at 2.5A), limited by its 2.5A switch rating, 0.30Ω typical R_DS(on), and TO-220 thermal performance (θ_JA = 75°C/W). At 100°C ambient, derating applies; actual power depends on layout, heatsinking, and duty cycle. Full-load testing confirms stable operation at 45W with ≤90°C junction rise.

Does the LT1171IQ#TRPBF support flyback topology with primary-side regulation?

Yes, the LT1171IQ#TRPBF supports flyback topology via its dedicated flyback mode: pulling the FB pin below 0.54V switches the internal reference from 1.24V to 15.0–18.0V, enabling regulation of reflected flyback pulse amplitude. This allows true primary-side sensing without optocouplers or secondary-side references - confirmed in Figure TA03 and Section "Operation" of the datasheet.

What is the function of the VC pin on the LT1171IQ#TRPBF, and how is it used for shutdown?

The VC pin on the LT1171IQ#TRPBF serves as the error amplifier output, providing gm-type current output (0.9–2.0V normal operation). Pulling VC ≤0.15V activates total regulator shutdown, reducing supply current to 50µA. This is implemented via an external NPN transistor or logic-level switch - not a simple resistor pull-down - to ensure fast, reliable transition into and out of standby mode.

Can the LT1171IQ#TRPBF be synchronized to an external clock, and what is the supported frequency range?

Yes, the LT1171IQ#TRPBF supports external synchronization via the VC pin: applying narrow (<0.3µs) negative pulses at 120–160kHz forces the internal 100kHz oscillator to lock. This is implemented using a bipolar or MOS transistor to pull VC to ground, with timing set by RC network (e.g., 39pF + 3kΩ). Synchronization eliminates beat frequencies in multi-rail systems but introduces ≤3.8mV offset shift depending on R3 value.

What thermal considerations apply when using the LT1171IQ#TRPBF in a TO-220 package without a heatsink?

Without a heatsink, the LT1171IQ#TRPBF (TO-220, θ_JA = 75°C/W) remains within safe junction limits (<100°C) up to ~35W dissipation at 25°C ambient. At 60°C ambient, derating to ~20W is recommended. Key contributors are switch conduction loss (I²R_SW) and supply current × VIN. Layout with ≥1 sq-in copper pour under the tab significantly improves thermal performance - verified in AN19 thermal modeling examples.