Analog Devices Inc. DC939A

Overview

LTC2484 from Analog Devices (formerly Linear Technology) is a 24-bit no-latency delta-sigma analog-to-digital converter with patented Easy Drive input current cancellation. It delivers 2 ppm INL, 1 µV offset error, 600 nV_RMS noise, and simultaneous 50 Hz/60 Hz line rejection - enabling direct digitization of high-impedance sensors (e.g., strain gauges, load cells) without external amplification in precision industrial weighing systems.

For engineers reviewing the LTC2484 datasheet, LTC2484 pinout, LTC2484 application, or LTC2484 equivalent, this page provides verified technical context, validated pin functions, real-world application mappings, and two confirmed alternative ADCs for sensor interface designs requiring rail-to-rail input, zero differential input current, and integrated line-frequency rejection.

Technical Context

The LTC2484 implements a third-order delta-sigma modulator with automatic transparent offset and full-scale calibration, eliminating drift over temperature and time. Its Easy Drive architecture cancels differential input current via passive sampling network, enabling direct connection to sensors with source impedances up to 100 kΩ while maintaining DC accuracy.

It supports programmable line-frequency rejection (50 Hz, 60 Hz, or simultaneous 50/60 Hz) and a 2× speed mode (15 Hz output rate using internal oscillator). The on-chip trimmed oscillator (307.2 kHz nominal) removes need for external crystals, and the reference voltage range spans 0.1 V to V_CC, independent of common-mode input.

Key Specifications

Pinout & Package

Package: 10-lead (3 mm × 3 mm) plastic DFN with exposed pad (Pin 11 = GND). Thermal resistance θ_JA = 43°C/W; exposed pad must be soldered to PCB ground plane for thermal and electrical integrity.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar high-precision delta-sigma ADC applications.

Compared with ADS124S08 and MAX11206, the LTC2484 uniquely combines zero differential input current, integrated simultaneous 50/60 Hz rejection, and rail-to-rail input - making it the only option among the three that supports direct, high-accuracy digitization of unbuffered 100 kΩ bridge sensors without external circuitry or firmware-based filtering.

Availability

LTC2484 is available at Aetrix Electronics and suitable for precision weight scales, industrial process control modules, and high-accuracy digital multimeters requiring stable component supply, long-term calibration integrity, and global line-frequency immunity.

Supply support for LTC2484 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 technologies, serving industrial, automotive, communications, and healthcare markets.

The LTC2484 belongs to ADI's precision delta-sigma ADC product line, designed specifically for direct sensor digitization in noise-sensitive, low-power, high-accuracy instrumentation - emphasizing ease of use, minimal external components, and guaranteed metrological performance.

FAQ

What is the maximum source impedance the LTC2484 can drive without accuracy loss?

The LTC2484's Easy Drive technology cancels differential input current, enabling accurate digitization of sensors with source impedances up to 100 kΩ without external buffering. This is confirmed by the "+FS Error vs RSOURCE" plot (Figure TA02), which shows <±20 ppm error at 100 kΩ with V_CC = 5 V and V_REF = 5 V. The LTC2484 maintains 2 ppm INL and 0.5 µV offset even under these conditions - a capability not shared by most competing 24-bit ADCs.

Does the LTC2484 require an external crystal or oscillator?

No, the LTC2484 does not require an external crystal or oscillator. It integrates a trimmed on-chip oscillator (307.2 kHz nominal) that eliminates external timing components. When fO is tied to GND, the device operates in internal oscillator mode - supporting default 50/60 Hz rejection and 7.5 SPS output rate. External clocks are optional for custom data rates or shifted filter nulls, but not necessary for standard operation of the LTC2484.

How does the LTC2484 achieve simultaneous 50 Hz and 60 Hz line-frequency rejection?

The LTC2484 achieves simultaneous 50 Hz and 60 Hz rejection through its programmable digital filter architecture, configured via the SDI pin. When set to "simultaneous mode," the internal delta-sigma modulator and decimation filter place nulls at both 50 Hz and 60 Hz (and harmonics) using a single 280 kHz external oscillator or internal clock derivative. This is verified in the Electrical Characteristics table (page 3) and Typical Performance graphs (G23–G25), confirming >87 dB rejection at both frequencies without external notch circuits.

Can the LTC2484 operate with a 2.5 V reference and 3.3 V supply simultaneously?

Yes, the LTC2484 supports independent reference and supply voltages: V_REF may be as low as 0.1 V and up to V_CC, so a 2.5 V reference with a 3.3 V V_CC is fully supported. The datasheet specifies performance (e.g., 2 ppm INL, 15 ppm total unadjusted error) under exactly these conditions (V_CC = 2.7–5.5 V, V_REF = 2.5 V), and the input common-mode range remains GND to V_CC regardless of V_REF value - ensuring robust operation in mixed-voltage systems using the LTC2484.

What is the function of the fO pin on the LTC2484?

The fO pin on the LTC2484 controls the conversion clock source. When pulled to GND, it selects the internal 307.2 kHz oscillator for default operation. When driven with an external square wave (10–1000 kHz), it overrides the internal clock to adjust output data rate or shift digital filter nulls - e.g., 280 kHz for simultaneous 50/60 Hz rejection. This pin directly determines conversion time (t_{CONV_1}/t_{CONV_2}) per the Timing Characteristics table (page 5), and its state is sampled at power-up or CS falling edge.