Analog Devices Inc. AD1885JST

Overview

AD1885JST from Analog Devices is a 16-bit stereo full-duplex AC'97 2.1-compliant audio codec IC designed as the analog front end for PC audio, modem, and DSP systems. It delivers >90 dB dynamic range, supports variable sample rates from 7040 Hz to 48 kHz in 1 Hz steps, integrates stereo headphone amplifiers with 6-bit volume control, and features PHAT™ Stereo 3D enhancement for desktop and notebook audio subsystems.

For engineers reviewing the AD1885JST datasheet, AD1885JST pinout, AD1885JST application, or AD1885JST equivalent, key selection criteria include AC'97 2.1 compliance, dual Σ∆ ADC/DAC architecture, jack sense–enabled automatic output switching, split 3.3 V digital / 5 V analog power supplies, and low-power mixer mode for mobile platforms.

Technical Context

The AD1885JST implements a dual-channel Σ∆ ADC and dual-channel Σ∆ DAC architecture with independent sample rate generation per channel, enabling simultaneous capture and playback at mismatched rates (e.g., 8 kHz modem + 44.1 kHz audio). Its analog mixer supports time-correlated I/O for host-based echo cancellation by routing mic data to ADC left and summed DAC output to ADC right.

It integrates Data Direct Scrambling (D2S) to suppress idle tones below quantization noise floor and push out-of-band artifacts beyond 20 kHz, while its 48-terminal LQFP package accommodates dedicated antialiasing (AFILT1/AFILT2) and AC-coupling (FILT_L/FILT_R) filter pins, plus CX3D/RX3D for PHAT™ 3D tuning.

Key Specifications

Pinout & Package

AD1885JST is housed in a 48-lead thin quad flatpack (LQFP), designated ST-48 per Analog Devices' ordering guide. The package supports standard reflow soldering and provides thermal resistance θ_JA = 76.2°C/W.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar audio codec applications.

Compared with AD1885JST, AD1886JST offers higher-resolution DAC output for critical listening applications, while ALC203 provides simplified integration and lower licensing cost at the expense of advanced audio features and modem capability.

Availability

AD1885JST is available at Aetrix Electronics and suitable for desktop PC motherboards, notebook audio subsystems, host-based modems, and gaming audio enhancements requiring stable component supply and long-term industrial availability.

Supply support for AD1885JST 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. is a global leader in high-performance analog, mixed-signal, and digital signal processing semiconductors, headquartered in Norwood, MA.

The AD1885JST belongs to Analog Devices' SoundPort® audio codec product line, engineered specifically to meet AC'97 2.1 specifications while delivering enhanced features like PHAT™ 3D, jack sensing, and variable-rate modem/audio coexistence.

FAQ

What is the primary function of the AD1885JST in an AC'97-compliant system?

The AD1885JST serves as the analog front end in AC'97 2.1-compliant systems, performing analog-to-digital conversion (ADC) for microphone and line inputs, digital-to-analog conversion (DAC) for line and headphone outputs, and analog mixing with programmable gain control. It interfaces with a digital audio controller via the AC'97 serial link (SYNC, BIT_CLK, SDATA_IN/OUT) and is essential for PC audio, modem, and DSP applications requiring high-fidelity, low-noise signal paths.

Does the AD1885JST support simultaneous audio and modem operation at different sample rates?

Yes, the AD1885JST supports independent sample rate generation for ADC and DAC channels, enabling concurrent operation at mismatched rates - for example, 8 kHz for V.34 modem data and 48 kHz for stereo audio playback. Its D2S rate generators provide 1 Hz resolution across 7040 Hz to 48 kHz, and selectable 8/7 and 10/7 multiplier coefficients ensure precise irrational rate synthesis required by V.34 standards.

How does the AD1885JST implement jack sense functionality, and what pins are involved?

The AD1885JST uses JS0 (Pin 47) and JS1 (Pin 48) as configurable jack sense inputs that detect plug insertion and automatically mute conflicting outputs. JS0 mutes MONO_OUT upon detection; JS1 mutes LINE_OUT and MONO_OUT (or LINE_OUT only, depending on configuration). Both pins can alternatively be programmed as general-purpose digital outputs or EAPD control signals, offering flexible hardware-assisted audio routing without host intervention.

What is the role of VREFOUT on the AD1885JST, and what load can it drive?

VREFOUT (Pin 28) is a 2.25 V precision voltage reference output designed to bias electret condenser microphones. It provides up to 5 mA of continuous current, sufficient to power two typical ECMs (each drawing ~0.5 mA) with stable DC bias. This eliminates the need for external bias circuitry and ensures consistent microphone sensitivity across varying supply conditions, directly supporting the AD1885JST's dual MIC1/MIC2 inputs with switchable 20 dB preamp.

Can the AD1885JST operate in low-power modes, and how is power consumption reduced?

Yes, the AD1885JST includes multiple hardware-controllable power-down modes accessed via the Power-Down Control register (Index 26h). Individual blocks - including ADC, DAC, analog mixer, and internal clocks - can be disabled. In full standby (all PR bits set), current drops to 0.1 mA (DVDD) and 0 mA (AVDD); in analog CD-only mode (AC-Link off), AVDD current falls to 12 mA. The mobile low-power mixer mode retains CD path activity while cutting total analog supply current to 7 mA, optimizing battery life in portable systems.