Analog Devices Inc. LT1587CT-1.5#PBF

Overview

LT1587CT-1.5#PBF from Analog Devices (formerly Linear Technology) is a fixed-output, low-dropout linear regulator delivering 1.5V at up to 3A with 1.3V typical dropout at full load. It features fast transient response, ±1% initial output voltage accuracy, and on-chip thermal limiting - engineered specifically for Intel Pentium Pro GTL+ bus termination supplies and other low-voltage logic applications requiring tight regulation under dynamic load steps.

For engineers reviewing the LT1587CT-1.5#PBF datasheet, LT1587CT-1.5#PBF pinout, LT1587CT-1.5#PBF application, or LT1587CT-1.5#PBF equivalent, key selection criteria include guaranteed dropout voltage at 3A, load regulation ≤0.05% typ, ripple rejection ≥60dB at 120Hz, thermal shutdown at ~150°C, and compatibility with low-ESR output capacitors down to 22µF tantalum.

Technical Context

The LT1587CT-1.5#PBF employs an internal NPN pass transistor architecture optimized for low-voltage operation, with separate thermal limits for control circuitry (125°C) and power transistor (150°C). Its frequency compensation enables stable operation with output capacitors as low as 22µF solid tantalum or 100µF aluminum electrolytic - critical for high-speed microprocessor GTL+ supply rails where ESR and ESL dominate transient response.

Unlike earlier LT1085-family regulators, the LT1587CT-1.5#PBF achieves lower dropout (1.3V vs. ~1.5V at 3A) and faster transient recovery while maintaining pin compatibility. However, it trades off maximum input voltage (7V absolute max) for improved performance - making it unsuitable for higher-input industrial or automotive linear regulation without external clamping.

Key Specifications

Pinout & Package

LT1587CT-1.5#PBF uses the industry-standard 3-pin TO-220 (T package) with exposed tab connected to VOUT. The case serves as the high-current output path and must be electrically isolated from heatsink if ground-referenced output is not required.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar low-dropout linear regulator applications.

Compared with LT1085CT-1.5, the LT1587CT-1.5#PBF delivers 0.2V lower dropout and 3× faster transient recovery but sacrifices 7V max VIN. Versus LT3080IM#PBF, it offers fixed 1.5V simplicity and TO-220 pin compatibility but lacks adjustability and higher input tolerance.

Availability

LT1587CT-1.5#PBF is available at Aetrix Electronics and suitable for Intel Pentium Pro GTL+ bus termination, low-voltage logic power supplies, and battery-powered instrumentation requiring stable component supply with commercial-grade temperature support (0°C to 125°C).

Supply support for LT1587CT-1.5#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 its portfolio of high-performance analog ICs, including precision regulators, data converters, and power management solutions.

The LT1587 product line was designed specifically for low-voltage, high-transient microprocessor supply applications - notably GTL+, SSTL, and HSTL bus termination - where traditional LDOs failed to meet speed and accuracy requirements.

FAQ

What is the maximum input voltage rating for the LT1587CT-1.5#PBF?

The LT1587CT-1.5#PBF has an absolute maximum input voltage of 7V. Exceeding this risks permanent damage. In typical GTL+ applications with 3.3V input, the 1.3V dropout leaves 1.8V headroom - sufficient for ripple and tolerance margins. Always verify VIN does not exceed 7V under any condition, including startup overshoot or fault scenarios.

Does the LT1587CT-1.5#PBF require an external protection diode?

No, the LT1587CT-1.5#PBF includes an internal input-to-output diode rated for 50–100A microsecond surge currents, eliminating the need for external protection in standard hot-plug or power-cycle scenarios. Only add a 1N4002 diode (as shown in Figure 2 of the datasheet) if a crowbar circuit could force instantaneous input short-to-ground with >1000µF output capacitance.

What output capacitor value and type are recommended for stable operation of the LT1587CT-1.5#PBF?

For guaranteed stability across all conditions, use ≥22µF solid tantalum (ESR <1Ω) or ≥100µF aluminum electrolytic on the output of the LT1587CT-1.5#PBF. Ceramic capacitors alone are insufficient due to near-zero ESR; a hybrid approach (e.g., 100µF tantalum + 1µF ceramic) improves high-frequency decoupling while maintaining low-frequency stability.

How does the thermal shutdown behavior of the LT1587CT-1.5#PBF differ from conventional LDOs?

The LT1587CT-1.5#PBF implements dual thermal shutdown zones: the control section shuts down at ~125°C, while the power transistor tolerates up to ~150°C. This prevents premature shutdown during localized heating and allows continued operation under partial heatsink failure - a key reliability feature for dense PCB layouts where thermal coupling between components is unavoidable.

Is the LT1587CT-1.5#PBF pin-compatible with the LT1085 family?

Yes, the LT1587CT-1.5#PBF is pin-compatible with the LT1083/LT1084/LT1085 family in TO-220 packaging (VIN-VOUT-GND pinout), enabling direct replacement in existing designs. However, note the reduced max input voltage (7V vs. 25–35V for LT1085) and improved transient response - verify input rail compliance before substitution.