Analog Devices Inc. LT1581CT7-2.5#PBF

Overview

LT1581CT7-2.5#PBF from Analog Devices (formerly Linear Technology) is a 10A fixed-output 2.5V low-dropout linear regulator with dual-supply architecture, remote sense capability, and 430mV dropout at full load. It delivers microprocessor core power on motherboards using separate 3.3V power and 5V control rails, achieving <1mV load regulation over 100mA–10A steps at the SENSE pin.

For engineers reviewing the LT1581CT7-2.5#PBF datasheet, LT1581CT7-2.5#PBF pinout, LT1581CT7-2.5#PBF application, or LT1581CT7-2.5#PBF equivalent, key selection criteria include its 2.5V ±0.6% initial accuracy, 7-lead TO-220 package with Kelvin-sense terminals, dual-input dropout optimization, fast transient response for CPU load steps, and guaranteed thermal performance up to 150°C junction temperature in the power section.

Technical Context

The LT1581CT7-2.5#PBF uses a dual-input NPN pass transistor architecture: VPOWER supplies output current while VCONTROL powers the regulation circuitry and provides ~1% of output current as base drive. This enables 100mV dropout at light loads and only 430mV at 10A - significantly lower than conventional LDOs - by driving the NPN into saturation without requiring VBE overhead.

It integrates remote sensing via dedicated SENSE and GND pins (Pin 3 and Pin 2), enabling true Kelvin feedback at the load to eliminate trace resistance effects. The ADJUST pin (Pin 1) is exposed on this fixed-voltage variant to allow external capacitor bypassing (0.1–1µF) for enhanced transient response and ripple rejection (≥55dB at 120Hz).

Key Specifications

Pinout & Package

Package: 7-lead plastic TO-220 (T7), tab connected to OUTPUT pin; electrically isolated mounting required due to output-connected case.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LTC3375EFE#PBF and TPS7A8300RGRT, the LT1581CT7-2.5#PBF uniquely combines 10A output, dual-supply dropout reduction, and dedicated Kelvin sense pins - making it irreplaceable for legacy high-current microprocessor core supplies where noise, accuracy, and transient response outweigh integration density.

Availability

LT1581CT7-2.5#PBF is available at Aetrix Electronics and suitable for microprocessor core supplies, high-current FPGA I/O banks, industrial PLC post-regulation, and portable computing power systems requiring stable component supply and long-term obsolescence support.

Supply support for LT1581CT7-2.5#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 full technical and manufacturing continuity for legacy Linear products including the LT1581 family.

The LT1581 series was designed specifically for next-generation microprocessor power delivery on desktop and portable platforms, addressing the need for ultra-low dropout, remote sensing, and dual-rail efficiency in 2.5V–3.3V core supply applications.

FAQ

What is the maximum allowable dropout voltage for stable operation of the LT1581CT7-2.5#PBF at 10A?

The LT1581CT7-2.5#PBF specifies a maximum dropout voltage of 430mV at 10A load - defined as the minimum (VPOWER – VOUT) required to maintain regulation. At 10A and TJ = 25°C, VPOWER must be ≥2.93V to sustain 2.5V output. Above 430mV, the device enters dropout and output voltage drops linearly with decreasing VPOWER.

Can the LT1581CT7-2.5#PBF operate with only a single input supply?

Yes, the LT1581CT7-2.5#PBF can operate as a single-supply device by connecting VPOWER and VCONTROL together. However, dropout is then determined solely by the minimum VCONTROL specification (≥1.02V above VOUT), resulting in higher effective dropout (~1.02–1.35V) compared to dual-supply mode. Full 430mV dropout performance requires separate 3.3V (VPOWER) and 5V (VCONTROL) rails.

Why does the LT1581CT7-2.5#PBF have an exposed ADJUST pin despite being a fixed-output device?

The LT1581CT7-2.5#PBF exposes the ADJUST pin to allow external capacitor bypassing (0.1–1µF to ground), which improves transient response and 120Hz ripple rejection by stabilizing the internal reference divider. This feature is unique to the LT1581 family among fixed-output LDOs and directly enhances dynamic performance during CPU load transients without requiring redesign of the feedback network.

How does remote sensing work on the LT1581CT7-2.5#PBF, and what is its practical benefit?

The LT1581CT7-2.5#PBF uses dedicated SENSE and GND pins to close the regulation feedback loop directly at the load terminals. This eliminates voltage errors caused by PCB trace resistance between the regulator and load - for example, a 10mΩ trace drop at 10A would cause 100mV error without sensing, but <1mV error with SENSE. It ensures ±0.6% output accuracy is maintained at the CPU socket, not just at the regulator output pin.

What thermal derating applies to the LT1581CT7-2.5#PBF at elevated ambient temperatures?

The LT1581CT7-2.5#PBF has two independent thermal limits: control section (125°C max, θJC = 0.65°C/W) and power transistor (150°C max, θJC = 2.50°C/W). At ambient temperatures above 70°C, junction temperature must be calculated separately for each section. For 10A operation with 4°C/W heatsink, max ambient is ~70°C before exceeding either limit - requiring active cooling or derating above that point.