Analog Devices Inc. LTC1285CS8#PBF

Overview

LTC1285CS8#PBF from Analog Devices (formerly Linear Technology) is a micropower 12-bit successive approximation ADC with differential analog input, single-supply operation (2.7V–6V), 160µA typical supply current at 7.5ksps, auto-shutdown to 1nA, and on-chip sample-and-hold - designed for battery-powered sensor interfaces and isolated data acquisition systems.

For engineers reviewing the LTC1285CS8#PBF datasheet, LTC1285CS8#PBF pinout, LTC1285CS8#PBF application, or LTC1285CS8#PBF equivalent, key selection criteria include guaranteed ±3/4 LSB DNL, 100µs conversion time, SPI/Microwire-compatible 3-wire serial interface, 12-bit unipolar transfer curve, and SO-8 package compatibility with space-constrained PCB layouts.

Technical Context

The LTC1285CS8#PBF implements a switched-capacitor SAR architecture with integrated sample-and-hold and rail-to-rail compatible digital I/O. Its differential input supports ratiometric measurements and reduced full-scale spans down to 1.5V, enabling direct connection to low-output sensors without gain stages.

It uses a synchronous 3-wire serial interface (CS/SHDN, CLK, DOUT) with MSB-first output format and null-bit preamble. Conversion is initiated by CS falling edge; no DIN pin or configuration word is required, distinguishing it from the multiplexed LTC1288 variant.

Key Specifications

Pinout & Package

Package: 8-lead plastic SO (SO-8), 150°C max junction temperature, θ_JA = 130°C/W.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar 12-bit micropower ADC applications.

Compared with ADS7822U and MAX11131ASA+, the LTC1285CS8#PBF uniquely delivers 12-bit resolution with sub-µA shutdown and differential input in SO-8 - making it irreplaceable for long-life, noise-sensitive, floating-sensor applications where every nanoamp counts.

Availability

LTC1285CS8#PBF is available at Aetrix Electronics and suitable for battery-operated systems, remote data acquisition, and isolated data acquisition requiring stable component supply and long-term manufacturability.

Supply support for LTC1285CS8#PBF 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 acquired Linear Technology in 2017 and maintains full product support, documentation, and manufacturing continuity for legacy Linear parts including the LTC1285 series.

The LTC1285CS8#PBF belongs to Linear's micropower precision ADC family, engineered specifically for ultra-low-power sensor signal conditioning in portable and remote instrumentation.

FAQ

What is the maximum clock frequency supported by the LTC1285CS8#PBF?

The LTC1285CS8#PBF supports a maximum clock frequency of 120 kHz when operating from a 2.7 V supply. At higher supply voltages (up to 6 V), the maximum clock frequency increases - e.g., ~200 kHz at 5 V - as confirmed in the "Maximum Clock Frequency vs Supply Voltage" plot (TPC21). Exceeding the rated frequency risks conversion errors due to insufficient internal settling time.

Does the LTC1285CS8#PBF require an external reference voltage?

Yes, the LTC1285CS8#PBF requires an external reference voltage applied to the VREF pin (Pin 1). It does not include an internal reference. The reference can range from 1.5 V to V_CC, and its value directly sets the full-scale input range - for example, a 2.5 V reference yields 610 µV per LSB resolution.

Can the LTC1285CS8#PBF operate from a 5 V supply?

Yes, the LTC1285CS8#PBF is fully specified for 2.7 V to 6 V single-supply operation. At 5 V, digital input thresholds scale accordingly (VIH ≈ 3.5 V, VIL ≈ 1.5 V), and maximum clock frequency increases to ~200 kHz. All DC and AC specifications remain valid across this range per the Recommended Operating Conditions table.

How does the auto-shutdown feature work in the LTC1285CS8#PBF?

The LTC1285CS8#PBF automatically enters shutdown mode when the CS/SHDN pin is driven high (to V_CC), reducing supply current to 1 nA typical. During active conversion (CS low), it draws 160 µA typical at 7.5 ksps. After conversion completes, internal bias circuits power down even if CS remains low - but full shutdown requires CS = V_CC.

What is the purpose of the null bit in the LTC1285CS8#PBF serial output?

The null bit is the first bit shifted out on DOUT after CS falls and before the 12-bit conversion result. It serves as a synchronization placeholder and indicates that the conversion is complete and valid data follows. The null bit is always '0', and subsequent bits are MSB-first (B11 through B0), enabling straightforward alignment with standard SPI shift registers.