Analog Devices Inc. LTC6421CUDC-20#TRPBF

Overview

LTC6421CUDC-20#TRPBF from Analog Devices (formerly Linear Technology) is a dual, matched, high-speed differential amplifier optimized as an ADC driver for 12–16-bit converters. It delivers fixed 20dB (10V/V) gain, ±0.1dB gain matching and ±0.2° phase matching at 100MHz, 1.3GHz –3dB bandwidth, and rail-to-rail output swing with adjustable 1V–1.6V common-mode voltage - enabling direct DC-coupled interface to precision ADCs in communications and instrumentation systems.

For engineers reviewing the LTC6421CUDC-20#TRPBF datasheet, LTC6421CUDC-20#TRPBF pinout, LTC6421CUDC-20#TRPBF application, or LTC6421CUDC-20#TRPBF equivalent, key selection criteria include channel-to-channel matching performance, VOCM-controlled output common-mode flexibility, low 6.2dB noise figure, high 80dB channel separation at 100MHz, and QFN-20 package compatibility with high-density mixed-signal PCB layouts.

Technical Context

The LTC6421CUDC-20#TRPBF integrates two fully independent differential amplifiers, each with internal 100Ω/1000Ω feedback networks setting fixed 20dB gain and 200Ω differential input impedance. Its on-chip output common-mode control loop (300MHz –3dB bandwidth) allows precise VOCM pin-driven biasing of differential outputs between 1V and 1.6V, eliminating need for transformers or AC-coupling capacitors.

Each channel features separate ENABLEx inputs for independent shutdown (reducing supply current to 1–3mA per amp), dedicated VOCMx pins, isolated V+ and V– supply paths, and 12.5Ω series output resistors enhancing stability across varying load conditions - supporting both single-ended-to-differential conversion and true differential signal processing up to 140MHz baseband.

Key Specifications

Pinout & Package

Package: 20-lead 3mm × 4mm × 0.75mm plastic QFN (UDC) with exposed thermal pad (Pin 21 = V–). All V– pins (3, 4, 13, 14, 21) must be connected to same ground/supply plane.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar differential ADC driver applications.

Compared with LTC6401CUDC-20#TRPBF, the LTC6421CUDC-20#TRPBF trades 3.3dB higher noise figure for 3.7× wider bandwidth and integrated dual-channel matching; versus LTC6400CUDC-20#TRPBF, it offers 50% smaller footprint and guaranteed inter-channel coherence at the cost of 6dB lower OIP3.

Availability

LTC6421CUDC-20#TRPBF is available at Aetrix Electronics and suitable for high-speed data acquisition, wireless infrastructure transceivers, and test & measurement equipment requiring stable component supply, matched dual-channel performance, and QFN-20 package compatibility.

Supply support for LTC6421CUDC-20#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, Inc. (acquired Linear Technology in 2017) is a global leader in high-performance analog, mixed-signal, and digital signal processing technologies, serving industrial, automotive, communications, and healthcare markets.

The LTC6421CUDC-20#TRPBF belongs to Linear's high-speed differential amplifier product line, engineered specifically for precision ADC driving in wideband communications and instrumentation - emphasizing channel matching, low noise, and flexible common-mode control.

FAQ

What is the operating temperature range for the LTC6421CUDC-20#TRPBF?

The LTC6421CUDC-20#TRPBF is specified for operation from 0°C to 70°C (Commercial grade). While characterized and expected to function from –40°C to 85°C, only the I-grade variant (LTC6421IUDC-20#TRPBF) is fully guaranteed across that extended range. Always verify ambient and junction temperature limits using θ_JA = 43°C/W in your thermal design.

Can the LTC6421CUDC-20#TRPBF drive ADCs with 50Ω differential input impedance?

Yes - the LTC6421CUDC-20#TRPBF can drive 50Ω differential ADC inputs directly. Its 25Ω differential output impedance allows clean matching via two 25Ω series resistors (one per output leg), or via a simple LC network. The datasheet confirms stable operation into 375Ω and open-circuit loads, confirming robustness with standard ADC termination schemes.

How does the VOCM pin affect the LTC6421CUDC-20#TRPBF output common-mode voltage?

The VOCM pin sets the output common-mode voltage for its associated channel (VOCMA → Channel A, VOCMB → Channel B) over a 1V–1.6V range. It is a high-impedance input; a 0.1μF bypass capacitor is mandatory. When tied to an ADC's VCM pin (e.g., LTC2285 at 1.5V), the LTC6421CUDC-20#TRPBF precisely tracks that reference, enabling transformerless DC-coupled interface with no level-shifting circuitry.

Is the LTC6421CUDC-20#TRPBF suitable for single-ended input applications?

Yes - the LTC6421CUDC-20#TRPBF supports single-ended input configuration without baluns. One input is driven through a matching network (e.g., 66.5Ω shunt resistor for 50Ω source), while the other is terminated to the same network. The internal feedback symmetry ensures balanced differential output swing and maintains distortion performance within 2–3dB of fully differential operation.

What is the maximum input common-mode voltage range for the LTC6421CUDC-20#TRPBF?

The LTC6421CUDC-20#TRPBF supports an input common-mode voltage range of 1V to 1.6V (min/max) under normal operation. This range aligns with its VOCM-adjustable output common-mode window, allowing direct connection to ADCs with similar VCM requirements. Exceeding this range may degrade CMRR or cause clipping - always reference the DC Electrical Characteristics table for temperature-dependent limits.