Maxim公司的MAX9877 D类放大器集成了高效率D类放大器和立体声AB类无电容的DirectDrive耳机放大器,是第三代无滤波器的D类放大器,具有辐射限制技术. MAX9877 D类功率放大器的THD+N为0.05%,能从3.7V电源向8欧姆负载提供高达725mW的功率,效率高达87%.MAX9877广泛应用在手机和手提媒体播放器.本文介绍了MAX9877的主要特性,方框图, 典型应用电路和MAX9877评估板的主要特性和详细电路图.

Low RF Susceptibility, Mono Audio Subsystem with DirectDrive Headphone Amplifier

The MAX9877 combines a high-efficiency Class D audio power amplifier with a stereo Class AB capacitorless DirectDrive® headphone amplifier. Maxim’s 3rd generation, filterless Class D amplifier with active emissions limiting technology provides Class AB performance with Class D efficiency.

The MAX9877 delivers up to 725mW from a 3.7V supply into an 8 ohm load with 87% efficiency to extend battery life.
The filterless modulation scheme combined with active emissions limiting circuitry and spread-spectrum modulation greatly reduces EMI while eliminating the need for output filtering used in traditional Class D devices.

The stereo Class AB headphone amplifier in the MAX9877 uses Maxim’s patented DirectDrive architecture, that produces a ground-referenced output from a single supply, eliminating the need for large DC-blocking capacitors, saving cost, space, and component height.
The device utilizes a user-defined input architecture, three preamplifier gain settings, an input mixer, volume control, comprehensive click-and-pop suppression, and I2C control. A bypass mode feature disables the integrated Class D amplifier and utilizes an internal DPST switch to allow an external amplifier to drive the speaker that is connected at the outputs of the MAX9877.

The MAX9877 is available in a thermally efficient, space-saving 20-bump WLP package.

MAX9877主要特性:
Low Emissions, Filterless Class D Amplifier Achieves Better than 10dB Margin Under EN55022 Class B Limits
Low RF Susceptibility Design Rejects TDMA Noise from GSM Radios
Input Mixer with User-Defined Input Mode
725mW Speaker Output (RSPK = 8ohm, PVDD = 3.7V)
53mW Headphone Output (RHP = 16ohm, VDD = 3.7V)
Low 0.05% THD+N at 1kHz (Class D Power Amplifier)
Low 0.016% THD+N at 1kHz (Headphone Amplifier)
87% Efficiency (RSPK = 8ohm, POUT = 750mW)
1.6Analog Switch for Speaker Amplifier Bypass
High Speaker Amplifier PSRR (72dB at 217Hz)
High Headphone Amplifier PSRR (84dB at 217Hz)
I2C Control
Hardware and Software Shutdown Mode
Click-and-Pop Suppression
Current-Limit and Thermal Protection
Available in a Space-Saving, 2.5mm x 2.0mm WLP
Package

主要应用:
Cell Phones
Portable Multimedia Players



图1. MAX9877方框图



图2.MAX9877典型应用电路

MAX9877评估板
The MAX9877 evaluation kit (EV kit) is an assembled and tested printed-circuit board (PCB) that evaluates the MAX9877 IC. The MAX9877 is a Class D audio power amplifier and stereo DirectDrive headphone amplifier communicating over a 2-wire I2C interface.
The MAX9877 features user-defined input configuration, input gain, input source, output enable, volume control, and oscillator frequency-modulation modes.

The user-defined features are programmed through the I2C-compatible serial interface, communicating at data rates up to 400kbps. The I2C data is sent through an on-board USB interface circuit using a computer or a user-supplied I2C bus.

The EV kit also features Windows 2000/XP/Vista®-compatible software that provides a user interface for exercising the MAX9877’s features. The program is menu driven and offers a graphical user interface (GUI) complete with buttons, checkboxes, and track bars.
MAX9877评估板主要特性:

Features
2.7V to 5.25V Single-Supply Operation
Proven Audio PCB Layout
On-Board USB Interface Circuit Generates
I2C-Compatible Signals
USB-PC Connection (Cable Included)
PCB Pads for User-Supplied I2C-Compatible Signals
PCB Pads for Audio Input and Output Signals
Evaluates the MAX9877EWP+TG45 in a 2mm x 2.5mm, 20-Bump, 5 x 4 WLP Package
Windows 2000/XP/Vista (32-Bit)-Compatible Software
Fully Assembled and Tested



图3.MAX9877 EV Kit评估板电路图(1)



图4.MAX9877 EV Kit评估板电路图(2)

来源：Maxim