Analog Devices Inc. LT1639IN

Overview

LT1639IN from Analog Devices (formerly Linear Technology) is a quad rail-to-rail input and output operational amplifier with Over-The-Top® capability, enabling operation with inputs up to 44V above the negative supply or above V+. It draws only 170μA per amplifier at 2.5V–44V total supply, delivers 25mA output current, and features 1.2MHz gain bandwidth and 0.4V/μs slew rate. It is used in battery monitoring, sensor conditioning, and 4mA–20mA transmitter circuits requiring wide common-mode range and micropower operation.

For engineers reviewing the LT1639IN datasheet, LT1639IN pinout, LT1639IN application, or LT1639IN equivalent, this page provides verified circuit role, validated 14-pin PDIP package mapping, confirmed Over-The-Top® input behavior, rail-to-rail I/O performance across 3V/5V/±15V supplies, and two field-validated alternative op amps for micropower quad rail-to-rail designs.

Technical Context

The LT1639IN implements dual complementary input stages (NPN and PNP) to achieve true Over-The-Top® operation: inputs remain functional even when driven >44V above V– or >0.3V above V+, with phase reversal protection and integrated 1kΩ series input resistors. Its internal compensation supports stable unity-gain operation and drives ≥200pF capacitive loads without external compensation.

It operates across total supply voltages from 2.5V to 44V, with reverse-battery protection up to –18V, no supply sequencing requirements, and guaranteed performance over –40°C to +85°C. Input common-mode range spans –0.4V to 44V on single supply and –15V to +29V on split supply, while CMRR remains ≥80dB across full range.

Key Specifications

Pinout & Package

LT1639IN is packaged in a 14-lead plastic PDIP (N package), with 0.300-inch body width, through-hole mounting, and JEDEC MS-001AC compliant footprint. Thermal resistance θ_JA = 130°C/W.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar quad rail-to-rail op amp applications.

Compared with TLV2474IDR and AD8604ARUZ, the LT1639IN uniquely supports inputs above V+ and V– while maintaining micropower operation - making it irreplaceable in high-common-mode industrial sensing where rail-to-rail I/O and Over-The-Top® tolerance are simultaneously required.

Availability

LT1639IN is available at Aetrix Electronics and suitable for battery monitoring systems, 4–20mA transmitters, portable sensor instrumentation, and micropower active filters requiring stable component supply across extended temperature ranges.

Supply support for LT1639IN 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, Inc. (ADI) is a global leader in high-performance analog, mixed-signal, and digital signal processing semiconductors, serving industrial, automotive, communications, and healthcare markets.

The LT1639IN belongs to ADI's legacy Linear Technology precision op amp product line, designed specifically for micropower, rail-to-rail, and Over-The-Top® operation in harsh industrial environments and battery-constrained portable equipment.

FAQ

What is the maximum input voltage the LT1639IN can tolerate relative to its supply rails?

The LT1639IN supports inputs up to 44V above V– and up to 0.3V above V+ - a feature known as Over-The-Top® operation. This means that even if V+ = 5V, an input of 49V is valid as long as it remains ≤44V above V–. The LT1639IN datasheet confirms this behavior applies to all four amplifier sections and is guaranteed across –40°C to +85°C.

Does the LT1639IN require external compensation for driving capacitive loads?

The LT1639IN is internally compensated to drive ≥200pF capacitively without oscillation. For loads >200pF up to 1000pF, optional external compensation - a 0.22μF capacitor in series with a 150Ω resistor from output to ground - is recommended. This configuration maintains stability across all output currents and supply voltages, as verified in the LT1639IN Typical Performance Characteristics (Figure 1638/39 G22).

Can the LT1639IN operate from a single 3V supply while maintaining rail-to-rail output swing?

Yes. The LT1639IN delivers rail-to-rail output swing on 3V single supply: output low is ≤8mV above V– at 5mA sink current, and output high is ≥2.94V at 5mA source current. Input common-mode range extends from –0.4V to 44V, allowing full utilization of the 3V supply range for sensor signal conditioning without clipping.

What is the reverse battery protection rating of the LT1639IN?

The LT1639IN provides reverse battery protection up to –18V on either supply rail. Under reverse supply conditions, supply current drops to <1nA, preventing damage and eliminating the need for external series diodes. This specification is tested and guaranteed per Absolute Maximum Ratings table in the LT1639IN datasheet.

How does the LT1639IN prevent phase reversal when inputs go below the negative supply?

The LT1639IN incorporates dedicated phase reversal protection circuitry that disables the input stage when inputs fall below V–, preventing false output polarity inversion. Combined with 1kΩ series input resistors and internal clamping, this ensures robust operation during transient faults - a key requirement in automotive and industrial current-sense applications where the LT1639IN is commonly deployed.