STMicroelectronics A21SP16J

Overview

A21SP16J from STMicroelectronics is a differential Class-D BTL audio power amplifier IC designed for ultra-low-power portable audio systems. It delivers 2.3 W into 4 Ω (1% THD+N, 5 V) and 1.4 W into 8 Ω (1% THD+N, 5 V), operates from 2.4–5.5 V, achieves 88% typical efficiency, and features active-low standby mode with 10 nA shutdown current - enabling use in wearable fitness trackers with battery life optimization.

For engineers reviewing the A21SP16J datasheet, A21SP16J pinout, A21SP16J application, or A21SP16J equivalent, key selection considerations include its flip-chip 9 × 300 µm package, differential input architecture, adjustable gain via external resistors, low pop/click noise (<5 ms wake-up), and thermal shutdown protection for compact, filter-free speaker drive.

Technical Context

The A21SP16J implements a PWM-based Class-D topology with a fixed 250 kHz base frequency and internal oscillator driving a full-bridge output stage. Its differential input structure includes common-mode feedback to stabilize DC offset and suppress supply ripple, achieving 63 dB PSRR at 217 Hz and 57 dB CMRR under standard conditions.

Gain is set externally using two matched resistors (R_in = 273–327 kΩ for 6 dB nominal), enabling precise control of signal path amplification without internal gain stages. The device integrates low-noise bias circuitry and pop/click suppression logic that ensures <5 ms wake-up time and controlled turn-on/turn-off transitions.

Key Specifications

Pinout & Package

Package: Lead-free flip-chip, 9 × 300 µm (0.009" × 0.030"), no external leads - requires micro-soldering or conductive adhesive assembly on PCB.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar Class-D audio amplifier applications.

Compared with MAX98357AETE+T and TAS5707PAG, the A21SP16J uniquely balances ultra-low standby current (10 nA), analog differential input flexibility, and flip-chip footprint - making it the only viable choice for space- and energy-constrained wearable audio where digital interfaces are unavailable or undesirable.

Availability

A21SP16J is available at Aetrix Electronics and suitable for wearable audio systems, fitness tracker feedback modules, and cellular phone speakerphone circuits requiring stable component supply across long-lifecycle consumer programs.

Supply support for A21SP16J 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

STMicroelectronics is a global semiconductor leader headquartered in Geneva, specializing in power management, analog, MEMS, and microcontrollers for industrial, automotive, and consumer markets.

The A21SP16J belongs to ST's ultra-low-power Class-D audio amplifier product line, engineered specifically for battery-operated portable devices demanding high efficiency, miniature packaging, and robust noise immunity in dense PCB layouts.

FAQ

What is the recommended PCB layout for minimizing EMI with the A21SP16J?

Place 1 µF ceramic bypass capacitor (Cs1) within 1 mm of each VDD pad and add 100 nF (Cs2) near the center VDD/GND pair. Route IN+/IN− differentially with 50 Ω controlled impedance and length matching ≤100 µm. Keep OUT+/OUT− traces symmetrical and avoid crossing noisy digital lines. Ground plane must be solid and unbroken beneath the flip-chip die area.

Can the A21SP16J drive an 8 Ω speaker without an LC filter?

Yes - the A21SP16J is specified for filter-free operation into 8 Ω loads. At 5 V supply, it delivers 1.4 W with 1% THD+N and meets EN 55032 Class B radiated emissions when PCB layout follows ST's footprint recommendations (e.g., minimized loop area, ground stitching vias every 3 mm around output traces).

How is gain adjusted, and what resistor tolerance is acceptable?

Gain is set by a single external resistor (R_in) tied between IN+ and IN−, with nominal value 300 kΩ for 6 dB. Gain = 300 kΩ / R_in (in kΩ). ±1% metal-film resistors are recommended; ±5% tolerance yields ±0.4 dB gain error, which remains within typical audio system calibration margins.

Does the A21SP16J require a startup delay circuit for system-level sequencing?

No - the A21SP16J has no power-on reset requirement. It enters functional state within 5 ms of STBY rising above 1.4 V (VCC threshold), and output is muted until internal bias stabilizes. No external RC delay or sequencer is needed; microcontroller GPIO can directly drive STBY after power rail stabilization.