Maxim 公司的MAX8821集成了用于白光LED的电荷泵，音频杨声器放大器和两个低噪音的LDO。高效率自适应模式电荷泵能以恒流方式驱动多达6个LED，而D类音频放大器则提供2W输出，能驱动4欧姆扬声器，每个LDO的输出电压能通过I2C接口单独编程，有高达70dB 的PSRR，广泛应用在手机和智能手机，PDA，数码相机和摄像机，MP3 播放器和 GPS设备。本文介绍了MAX8821的主要性能，方框图以及典型应用电路图。
The MAX8821 integrates a charge pump for white LEDs, an audio loudspeaker amplifier, and two lownoise LDOs controlled by an I2C control interface. The high-efficiency, adaptive-mode inverting charge pump drives up to six LEDs with constant current for uniform brightness. The LED current is controlled by an I2C interface and adjusts from 0.1mA to 25.6mA per LED into 32 pseudo-logarithmic steps. Independent voltages for each LED maximize efficiency even with large LED forward voltage (VF) mismatch. An internal temperature derating function reduces the current above +40°C to protect the LEDs.
The high-efficiency mono Class D audio amplifier delivers up to 2W into a 4speaker from a 5V input supply. The amplifier features proprietary filterless Active Emissions Limiting (AEL) technology. AEL prevents high-frequency emissions resulting from conventional Class D free-wheeling behavior in the presence of an inductive load. The amplifier offers two modulation schemes: a fixed-frequency mode (FFM) and a spreadspectrum mode (SSM) that reduce EMI-radiated emissions due to the modulation frequency. The amplifier also has robust output protection and high power-supply
rejection ratio (PSRR). Click-and-pop suppression is active during power-up/down, enable/disable, and for all mode changes. The amplifier’s gain is adjustable through an I2C interface, from -3dB to +24dB in 10 3dB steps. Differential inputs improve common-mode noise rejection.
The LDOs in the MAX8821 are designed for low-noise operation. Each LDO output voltage can be individually programmed by the I2C interface. Both LDO1 and LDO2 have a high 70dB PSRR rating.
The MAX8821 includes soft-start, thermal shutdown, open-circuit, and short-circuit protections, and is available in a compact 28-pin, Thin QFN, 4mm x 4mm package
(0.8mm max height).
应用：
Cell Phones and Smartphones
PDAs, Digital Cameras, Camcorders
MP3 Players, GPS Devices
主要特性：
White LED Inverting Charge Pump
Independent Adaptive Current Regulators for Each LED
6 Low-Dropout Current Regulators
Flexible I2C Dimming Control for Each LED
Ramp-Up/Down, Current Control for Each LED
Low 70μA (typ) Quiescent Current
TA Derating Function Protects LEDs
Mono 2W Class D Loudspeaker Amplifier
85% Efficiency (RL = 8, POUT = 600mW)
Low 0.05% THD+N at 1kHz
High 65dB PSRR at 1kHz
Fully Differential Inputs
-3dB to +24dB Gain Settings in 3dB Steps
Integrated Click-and-Pop Suppression
Low Quiescent Current
Dual Low-Noise LDO
45μVRMS Output Noise, 70dB PSRR
Flexible I2C-Controlled Output Voltages
200mA and 300mA Output Current Drive
图1. MAX8821方框图
图2. MAX8821典型应用电路图
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