Analog Devices Inc. DC846A

Overview

LTC2446 from Analog Devices (formerly Linear Technology) is a 24-bit, 8-channel delta-sigma ADC with integrated 4-terminal multiplexer and five selectable differential reference inputs. It delivers 15ppm absolute accuracy, 200nV_RMS noise at 13.8Hz, and up to 8kHz output rate in 2× mode - enabling high-precision ratiometric measurements of RTDs, strain gauges, and bridge sensors in industrial weighing and pressure transmitters.

For engineers reviewing the LTC2446 datasheet, LTC2446 pinout, LTC2446 application, or LTC2446 equivalent, this page provides verified technical context, validated pin functions, confirmed ratiometric multiplexing capability, real-world noise vs. speed trade-offs, and two rigorously cross-checked alternative ADCs for multi-reference sensor systems.

Technical Context

The LTC2446 employs a proprietary third-order delta-sigma modulator with on-the-fly offset and full-scale calibration every conversion cycle, ensuring stable 15ppm INL and <5µV offset over –40°C to 85°C. Its 19-input/4-output analog multiplexer supports simultaneous selection of differential input channel (CH0–CH7) and dedicated differential reference pair (VREF01±, VREF23±, VREF45±, VREF67±, or VREFG±), enabling true ratiometric digitization without external switching.

It operates via a 4-wire SPI-compatible interface (CS, SDI, SDO, SCK) with dual clock modes: internal oscillator (no external components) or external f_O up to 12MHz. Conversion latency is zero in 1× mode - the first result after any channel/reference/speed change is valid - supporting 4kHz multiplexing scan rates with no settling delay.

Key Specifications

Pinout & Package

38-lead plastic QFN (5mm × 7mm), exposed pad (Pin 39) tied to GND. All seven ground pins (1, 4, 5, 6, 31, 32, 33) must be soldered to PCB ground plane for optimal noise immunity and thermal dissipation.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar multichannel, ratiometric delta-sigma ADC applications.

Compared with ADS124S08 and MAX11206, the LTC2446 uniquely integrates five independent differential reference inputs with zero-latency multiplexing - making it the only option among the three that supports true concurrent ratiometric digitization of up to four separate bridge/RTD sensors without external components or timing coordination.

Availability

LTC2446 is available at Aetrix Electronics and suitable for industrial weighing systems, pressure transmitter front-ends, and direct temperature measurement applications requiring stable component supply, long-term calibration retention, and guaranteed ratiometric accuracy.

Supply support for LTC2446 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 LTC2446 belongs to ADI's precision delta-sigma ADC product line, designed specifically for high-accuracy sensor signal conditioning in demanding industrial and test equipment applications where ratiometric integrity and zero-latency multiplexing are critical.

FAQ

What is the maximum multiplexing rate supported by the LTC2446?

The LTC2446 supports up to 4kHz multiplexing rate when using an external oscillator (f_O). This is achieved with zero settling time between channel changes - the first conversion after selecting a new input/reference combination is fully accurate. The rate scales linearly with f_O, and the device maintains guaranteed modulator stability and lock-up immunity across all operating conditions specified in the datasheet.

Does the LTC2446 require external components for basic operation?

No, the LTC2446 operates with no external components for core functionality: its internal oscillator eliminates the need for crystals or capacitors, and its integrated 19-input/4-output multiplexer handles all analog routing. Only standard power supply decoupling (10µF tantalum + 0.1µF ceramic on V_CC) and proper grounding of all seven GND pins are mandatory. External buffers or gain stages are optional and only needed for specific signal conditioning requirements.

How does the LTC2446 achieve ratiometric accuracy across multiple sensors?

The LTC2446 achieves ratiometric accuracy through hardware-enforced 4-terminal switching: each selected differential input channel (e.g., CH0–CH1) is simultaneously paired with a dedicated differential reference input (e.g., VREF01+ and VREF01–). This ensures the ADC's full-scale range scales precisely with the excitation voltage applied to that sensor, rejecting supply and reference drift. Four such independent reference pairs plus a global reference (VREFG±) enable concurrent ratiometric measurement of up to four sensors.

What is the significance of the "no latency" mode in the LTC2446?

"No latency" mode means the first conversion result after any configuration change - including channel, reference input, oversampling ratio (OSR), or speed mode - is fully accurate and meets all specifications. There is no filter settling delay or invalid "dummy" conversions. This enables deterministic real-time scanning of multiple sensors at up to 4kHz without software overhead for discard cycles or timing compensation - a key differentiator versus conventional delta-sigma ADCs.

Can the LTC2446 interface directly with an RTD without external amplification?

Yes, the LTC2446 can interface directly with 2-, 3-, or 4-wire RTDs using its 4-terminal switching architecture. By applying excitation current through external resistors and routing both RTD voltage sense leads to differential input pins (e.g., CH0/CH1), while connecting the same excitation voltage to a matched reference pair (e.g., VREF01±), the LTC2446 performs true ratiometric measurement. Its ±0.5•V_REF input range and GND-to-V_CC common-mode support accommodate typical RTD bridge outputs without gain stages.