Analog Devices Inc. DC956A

Overview

LTC2485 from Analog Devices (formerly Linear Technology) is a 24-bit delta-sigma analog-to-digital converter with I²C interface, Easy Drive input current cancellation, and integrated oscillator. It delivers 2 ppm INL, 1 ppm offset error, rail-to-rail input range (0 V to V_CC), and programmable 50 Hz/60 Hz line rejection - enabling high-accuracy digitization of high-impedance sensors in industrial instrumentation and precision weighing systems.

For engineers reviewing the LTC2485 datasheet, LTC2485 pinout, LTC2485 application, or LTC2485 equivalent, key selection considerations include its differential input current cancellation (IDIFF = 0), simultaneous 50/60 Hz rejection capability, 10-lead DFN package with exposed pad, internal oscillator eliminating external crystals, and support for six I²C addresses plus global sync.

Technical Context

The LTC2485 employs a third-order delta-sigma modulator with automatic offset and full-scale calibration, achieving no-latency digital filter settling in a single cycle. Its patented Easy Drive sampling scheme cancels differential input current dynamically, allowing direct connection to sensors with source impedances up to 100 kΩ without accuracy degradation.

It supports dual-speed operation (1× and 2× modes), configurable line-frequency rejection (50 Hz, 60 Hz, or simultaneous), and flexible reference handling (V_REF as low as 100 mV or tied to V_CC). The on-chip temperature sensor and I²C-compatible interface enable system-level integration without external timing components.

Key Specifications

Pinout & Package

The LTC2485 is housed in a 10-lead (3 mm × 3 mm) plastic DFN package with exposed pad (Pin 11), which must be soldered to PCB ground for thermal and electrical performance.

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 LTC2485 uniquely combines I²C compatibility, zero differential input current, simultaneous 50/60 Hz rejection, and internal oscillator - making it the only option among the three that eliminates both external timing components and input buffering for high-Z sensor interfaces.

Availability

LTC2485 is available at Aetrix Electronics and suitable for precision weighing systems, industrial process controllers, laboratory instrumentation, and high-reliability sensor modules requiring stable component supply and long-term availability.

Supply support for LTC2485 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 LTC2485 belongs to ADI's precision delta-sigma ADC product line, designed specifically for high-accuracy, low-power, direct-sensor-digitization applications where input impedance, line noise, and calibration stability are critical.

FAQ

What is the maximum source impedance the LTC2485 can drive without accuracy loss?

The LTC2485 uses patented Easy Drive technology to cancel differential input current, enabling accurate digitization with source impedances up to 100 kΩ on both IN+ and IN– inputs. This eliminates the need for external op-amp buffers in applications like thermistor or RTD measurement, preserving DC accuracy and simplifying signal chain design. The LTC2485 achieves this while maintaining 2 ppm INL and 1 µV offset error across its full operating range.

Does the LTC2485 require an external crystal or oscillator?

No, the LTC2485 includes an on-chip trimmed oscillator, eliminating the need for external timing components in standard configurations. However, Pin CA0/f0 supports optional external clock input (10–1000 kHz) for applications requiring precise filter null placement - such as custom line-frequency rejection or synchronization across multiple LTC2485 devices. The internal oscillator operates at ~307.2 kHz for 60 Hz rejection mode.

How many I²C addresses does the LTC2485 support?

The LTC2485 supports six unique I²C addresses via two address pins (CA1 and CA0/f0), each configurable as LOW, HIGH, or floating - yielding 3 × 2 = 6 combinations. Additionally, it responds to a global address (0x00) for broadcast configuration or synchronized conversion start across multiple devices on the same bus, simplifying multi-ADC system design without address conflicts.

What is the conversion time for the LTC2485 in 50 Hz rejection mode?

In 1× speed mode with 50 Hz line rejection, the LTC2485 has a typical conversion time of 157.2 ms. In 2× speed mode under the same condition, it reduces to 78.7 ms. These times include full internal calibration and digital filtering; the result is available immediately after conversion completes, with no latency in data output due to its no-latency filter architecture. The LTC2485 holds the result in a static shift register during sleep mode until read via I²C.

Can the LTC2485 measure temperature directly?

Yes, the LTC2485 integrates a factory-trimmed PTAT (proportional-to-absolute-temperature) sensor with a typical output of 420 mV at 27°C. This on-chip sensor can be selected via the configuration register and read alongside analog inputs, enabling dual-purpose operation - for example, compensating bridge sensor drift using on-die temperature data. The LTC2485 delivers this functionality without requiring external temperature ICs or additional ADC channels.