NXP 公司的TFA9881是 3.4W 脉冲密度调制(PDM)输入D类音频放大器,它的输入接口是过取样的脉冲密度调制(PDM)码流,通过该接口接收音频和控制设定如静音,增益,脉宽调制(PWM)输出斜率,剪辑控制和扩展带宽.工作电压2.5V-5.5V,对于4欧姆/20uH的负载效率高达90%,输出噪音电压24uV,信噪比为103dB,主要用在手机,PDA,手提游戏机,PND,笔记本电脑/上网本以及MP3播放器/PMP等.本文介绍了TFA9881主要特性和优势,方框图和典型的立体声应用电路.
TFA9881: 3.4 W PDM input class-D audio amplifier
The TFA9881 is a mono, filter-free class-D audio amplifier in a 9-bump WLCSP (Wafer
Level Chip-Size Package) with a 400um pitch.
The digital input interface is an over-sampled Pulse Density Modulated (PDM) bit stream.
The TFA9881 receives audio and control settings via this interface. Dedicated silence patterns are used to configure the control settings of the device, such as mute, gain, Pulse Width Modulated (PWM) output slope, clip control and bandwidth extension (this control mechanism is not required if the default settings are used). The Power-down to Operating mode transition is triggered when a clock signal is detected.
The device features low RF susceptibility because it has a digital input interface that is insensitive to clock jitter. The second order closed loop architecture used in the TFA9881 provides excellent audio performance and high supply voltage ripple rejection.

TFA9881主要特性和优势:
Small outline WLCSP9 package: 1.3x 1.3x 0.6 mm
Wide supply voltage range (fully operational from 2.5 V to 5.5 V)
High efficiency (90 %, 4ohm/20 uH load) and low power dissipation
Quiescent power:
6.5 mW (VDDD = 1.8 V, VDDP = 3.6 V, 4ohm/20 uH load, fclk = 2.048 MHz)
7.8 mW (VDDD = 1.8 V, VDDP = 3.6 V, 4ohm/20 uH load, fclk = 6.144 MHz)
Output power:
1.4 W into 4ohm at 3.6 V supply (THD = 1 %)
2.7 W into 4ohm at 5.0 V supply (THD = 1 %)
3.4 W into 4ohm at 5.0 V supply (THD = 10 %)
Output noise voltage: 24uV (A-weighted)
Signal-to-noise ratio: 103 dB (VDDP = 5 V, A-weighted)
Fully short-circuit proof across load and to supply lines
Current limiting to avoid audio holes
Thermally protected
Undervoltage and overvoltage protection
High-pass filter for DC blocking
Invalid data protection
Simple two-wire interface for audio and control settings
Left/right selection
Three gain settings:3 dB, 0 dB and +3 dB 
PWM output slope setting for EMI reduction
Bandwidth extension to support low sampling frequencies
Clip control for smooth clipping
Mute mode
‘Pop noise’ free at all mode transitions
Short power-up time: 2 ms
Short power-down time: 5us 
1.8 V/3.3 V tolerant digital inputs 
Low RF susceptibility 
Insensitive to input clock jitter 
Only two external components required

TFA9881应用:
Mobile phones
PDAs
Portable gaming devices
Portable Navigation Devices (PND)
Notebooks/Netbooks
MP3 players/Portable media players