Analog Devices Inc. AD1981AJST

Overview

AD1981AJST from Analog Devices is an AC '97 2.2-compliant stereo audio codec IC with integrated headphone amplifier, S/PDIF output, and jack sense support. It delivers 20-bit DAC resolution, 16-bit ADC resolution, >90 dB dynamic range, and variable sample rate operation from 7.04 kHz to 48 kHz - used in PC motherboard audio subsystems for legacy AC '97 platform integration.

For engineers reviewing the AD1981AJST datasheet, AD1981AJST pinout, AD1981AJST application, or AD1981AJST equivalent, key selection criteria include AC '97 link interface compliance, dual-supply operation (3.3 V digital / 5 V analog), 48-lead LQFP package, and programmable microphone preamp gain with jack-sense–driven automatic output switching.

Technical Context

The AD1981AJST implements a full-duplex AC '97 serial interface with BIT_CLK (12.288 MHz), SYNC, SDATA_IN/OUT, and RESET signals. Its internal architecture includes separate 16-bit ADC and 20-bit DAC paths, analog input selector with CD ground reference, and digital equalizer coefficient storage for speaker optimization.

It supports split power domains (DVDD = 3.3 V, AVDD = 5.0 V), features six independent power-down control bits (PR0–PR6) enabling granular current reduction down to 1 mA, and integrates VREFOUT (2.25 V nominal, 5 mA drive) for microphone bias and external amplifier control.

Key Specifications

Pinout & Package

AD1981AJST is housed in a 48-lead thin quad flatpack (LQFP) package with exposed thermal pad (ST-48). Pin 1 identifier located at top-left corner; pins arranged in counter-clockwise order.

Key Features

Applications

Equivalent & Alternatives

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

Compared with AD1981AJST, AD1980A omits S/PDIF and jack sense - reducing feature set but lowering cost; AK4531VN requires external amplification and lacks VREFOUT, increasing BOM count and layout complexity despite similar AC '97 functionality.

Availability

AD1981AJST is available at Aetrix Electronics and suitable for desktop PC motherboards, industrial HMIs, VoIP terminals, and legacy embedded audio systems requiring stable component supply and long-term lifecycle support.

Supply support for AD1981AJST 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 AD1981A product line was designed specifically for AC '97–based PC audio subsystems, emphasizing integration of codec, headphone driver, S/PDIF output, and system-level power management in a single 48-lead LQFP package.

FAQ

What is the maximum sample rate supported by the AD1981AJST?

The AD1981AJST supports a maximum sample rate of 48 kHz for both DAC and ADC paths. It also operates down to 7.04 kHz with 1 Hz resolution, enabling flexible use in voice, telephony, and multimedia applications. The device uses internal PLL and sample rate generators to maintain jitter performance across the full range.

Does the AD1981AJST include a built-in headphone amplifier?

Yes, the AD1981AJST includes a fully integrated stereo headphone amplifier capable of delivering 1 Vrms into 32 Ω loads with <–75 dB THD. This eliminates the need for external op-amps in most PC and embedded audio designs and is controlled via dedicated volume and mute registers (Index 04h).

What power supply voltages does the AD1981AJST require?

The AD1981AJST requires two independent supplies: 5.0 V ±5% (AVDD) for the analog section including ADC, DAC, and headphone amplifier; and 3.3 V ±5% (DVDD) for digital logic, AC '97 interface, and register control. Separate analog and digital ground planes (AVSS/DVSS) must be used per datasheet layout guidelines.

Can the AD1981AJST generate its own AC '97 bit clock?

Yes, the AD1981AJST can generate BIT_CLK internally using its on-chip 24.576 MHz crystal oscillator (XTL_IN/XTL_OUT). In primary mode, it drives BIT_CLK at 12.288 MHz; in secondary mode, it accepts an external BIT_CLK. The device supports both configurations via register-controlled mode selection.

What is the function of the VREFOUT pin on the AD1981AJST?

The VREFOUT pin on the AD1981AJST provides a programmable 2.25 V reference output with 5 mA drive capability. It is used for microphone biasing and external amplifier power-down control (EAPD). Its voltage and enable state are configured via register 76h and extended audio control registers.