文献翻译—NCP2890音频功率放大器

Abstract: ON Semiconductor (OnSemi) Company A-B-type main NCP2890 audio power amplifier performance characteristics and the basic working principle, give the design of the NCP2890 audio amplifier with a typical application circuit and design method. Key words: NCP2890; AB type; audio amplifier1 outlines ON Semiconductor NCP2890 are (OnSemi) has introduced cost-effective, full-featured audio Series Products of the first audio power amplifier, it is designed for mobile phone and PDA, such as battery-powered wireless devices designed for production, are one kinds of very good quality wireless applications A-B-type audio power amplifier can provide customers with superior audio performance. The device has a superior power supply rejection ratio (PSRR) and total harmonic distortion plus noise (THD + N) characteristics at the same time, a combination of external control gain characteristics and adjustable boot and shutdown time delay function, and have a startup and shutdown control circuit that can eliminate the opening and closing of such audio power amplifier generated audible noise, can be flexibly used in portable audio equipment design. NCP2890 allows lithium-ion or lithium polymer battery direct power supply, and thus obviates the extra Low Dropout Regulators (LDO), while reducing board space and reduces the overall cost. 2-chip structure and performance parametersTo meet the specific needs of the market, NCP2890 currently have Mi-crobump-9 (2.25mm2) and Micro-8 (14.7mm2) two different kinds of packaging forms, shown in Figure 1 with its pin diagram, all cited the function of the foot such as Table 1 NCP2890 include 671 internal transistor, MOS gate 1899, which has excellent audio performance, Table 2 give the NCP2890 the main performance parameters. Table 2NC2890 main performance parameters3 Application Circuit Design Figure 2 shows a typical NCP2890 audio amplifier application circuit, Figure 2 can be seen from, NCP2890 external only used to adjust the gain of the two resistors, an input coupling capacitor, a bypass capacitor, such as a small number of components, therefore the external requirements devices extremely easy3.1 Working Principle circuitNCP2890 contains two identical power amplifiers, the input audio signal by the first power amplifier amplified the output from the OUTA. Voltage gain by external resistor Rf and Rin the ratio of the decision. The audio signal amplified by the gain of one and then the second power amplifier RP enlarge, and OUTB output. Because of OUTA and OUTB client-side audio output signal power equal to the size, phase contrast, and two outputs (OUTA and OUTB) DC the same static potential (Vp / 2), so, speakers can be connected directly to the client OUTA and OUTB , rather than increase the output coupling circuit. Two power amplifier output stage using PMOS and NMOS transistors by the special design. Normal conduction, the channel resistance of less than 0.6, and thus its output waveform distortion is very small.General power amplifier in the open and turn off the process will produce the human ear can hear the noise, in order to eliminate audible noise, in-house designed NCP2890 noise elimination circuit. Boot time, add the switch control logic high end of bypass capacitor Cby on the DC voltage values begin to increase exponentially when the voltage value reaches the value of common-mode voltage (Vp / 2) when the beginning of output power (this process around 50ms); and shutdown, the control low-level termination, load to be connected to the grounding terminal, the output power to zero, when the DC circuit quiescent current less than 100nA3.2 circuit element parametersRin and Rf amplifier used to set the closed-loop gain, NCP2890 in order to optimize the performance of the closed-loop gain amplifier should be set at a relatively low level, THD at this time the smallest, the largest signal to noise ratio, wide frequency response range. So in most cases, the closed-loop gain amplifier installed in general between 2 5, therefore, input resistance (Rin) values of D in the 20k more appropriate, and Rf is used to adjust the closed-loop gain to control the output power. Input coupling capacitor Cin input amplifier used to isolate the DC voltage, Rin simultaneously with the formation of a high-pass filter, but it will affect the filter cutoff frequency threshold. In order to enable the low-frequency signals do not decay too great, in theory, Cin should take a larger value, while the larger capacitor charge and discharge time is long, therefore, required a longer period of time to make input to reach the static potential Vp / 2, which is easy to make the output noise generated boot. Therefore, in most cases, Cin values generally between 0.1 0.39F more appropriate (Rin = 20k pm). Bypass capacitor Cby are common-mode voltage (Vp / 2) of the filter, is to determine the length of the boot, boot noise reduction as a key component, in most cases, 1.0F bypass capacitor Cby check more appropriate. R1 and R2 components of the partial pressure circuit chips used to produce the start voltage, general R1 value 100k, designed according to voltage value to select the resistance R2, as long as the pressure so that the value is greater than 1.2V can be about3.3 CautionWhen the circuit reaches the maximum output power Porms = 1.0W, Vp = 5.0V, RL = 8.0 when the load on the peak current of 500mA. In order to prevent the output load circuit when the output current is too large, set up chip output current detection circuit, it can be limited to a maximum output circuit 800mA. In this way, once the output current of over 800mA, the output side of the four MOS transistors will be gated off and no longer voltage output current. When the chip temperature exceeds 160 , the internal amplifier will be shut down and stop working until the temperature is below 140 , the internal amplifier to begin work to restart. Despite the NCP2890 contains an internal over-current and over-temperature protection circuit, but when in use, we must pay attention to power supply voltage should not exceed their limits, so as to avoid chip damage.摘要：介绍了安森美半导体(OnSemi)公司类音频功率放大器 NCP2890的主要性能特点和基本工作原理，给出了用 NCP2890设计音频功放的典型应用电路和设计方法。 关键词：NCP2890；A-B 类；音频放大器1 概述是安森美半导体()公司推出的经济高效、功能齐备的音频系列产品中的第一款音频功率放大器，它是专为手机和等电池供电的无线设备而设计生产的，是一种质量非常优秀的无线应用类音频功率放大器，可为客户提供卓越的音频性能。该器件在具有出众的电源抑制比()和总谐波失真加噪声()特性的同时，综合了外部控制增益特征和可调式开机与关机延时功能，并具有“开机和关机”控制电路，能消除开启和关闭此类音频功率放大器时产生的可听噪声，可灵活应用于便携式音频设备的设计中。允许锂离子或锂聚合物电池直接供电，因而省却了额外的低压降稳压器()，同时减少了电路板的占用空间并降低了整体成本.2 芯片结构与性能参数为满足特定市场的需求，目前有-()和()两种不同的封装形式，图所示为其引脚排列图，各引脚的功能如表列. 内部包括个晶体管、个门电路，因而具有极佳的音频性能，表给出了的主要性能参数.应用电路设计图所示为音频功放的典型应用电路，由图可见，外围只有用来调节增益的两个电阻、一个输入耦合电容、一个旁路电容等少数几个元件，因此所需外围器件极其简单电路工作原理内含两个完全一样的功率放大器，输入的音频信号经第一个功率放大器放大后从输出。电压增益由外接电阻与的比值决定。放大后的音频信号再经增益为的第二个功率放大器进行反相放大，并从输出。由于端与端输出的音频功率信号大小相等、相位相反，且两个输出端(和)的直流静态电位相同（），所以，扬声器可以直接连接到与端，而不用增加输出耦合电路。两个功率放大器的输出级均采用和晶体管特殊设计而成。正常导通时，其沟道电阻小于，因而其输出波形失真非常小. 一般的功率放大器在开启和关闭