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1、IC 基本电气特性 Quiescent current 静态电流 Standby current低功耗电流 Dropout voltage(LDO特性)压降的输入电压 Efficiency功率 Transient response顺势特性 Line regulation线路调整器 Load regulation负载调整率 Power supply rejection电源排除/抑制 Noise Accuracy精确性 IC 量测 IC（LDO)结构框图 Capacitor 电容 reference 参考(电压）error amplifier 误差信号放大器 Pass element 无源元件（二
2、极管）dynamic load 动态负载 主要模块包括;Voltage Reference 参考（电压）Error Amplifier 误差信号放大器 Feedback Network 反馈网络 Series-pass Element 无源元件（二极管）优点:简单、输出纹波电压低、出色的 line 和负载稳压、对负载和 line 的变化响应迅速、电磁干扰（EMI)低 缺点：效率低、如果需要冷却设备，则要求较大的空间 IC基本电气特性 Quiescent Current&Standby Current Quiescent Current(Ground current)：The differenc
3、e between input and output。Low quiescent current is necessary to maximize the efficiency。低静态电流是最大限度地提高效率必要条件。Standby Current：The input current drawn by a regulator when the output voltage is disabled by a shutdown signal.Quiescent Current and Output Current The value of quiescent current is mostly d
4、etermined by the series pass element，topologies，ambient temperature,etc.静态电流的值主要是一系列无源元件，拓扑结构，环境温度等 确定的 具体特性与IC结构、制程密切相关 IC基本电气特性 Dropout Voltage（特有规格)Low-Dropout Linear Regulators 低压差线性稳压器 传统的三端稳压器如:LM78xx Vdrop 的典型值是 2V,看到很多 7805 应用 时都会背着一个散热器.LM317 2V LM1117 1。2V。调整管采用的结构 LM317 输出 Darlingtong Vdr
5、op=Vsat+2Vbe 1。62。5V NPN Vdrop=Vsat+Vbe 0.9V PNP Vdrop=Vsat 0。150。4V PMOS Vdrop=Io X Ron 35350mv NMOS Vdrop=Vsat+Vgs 1V 不同调整管结构的比较:1 The NMOS pass element is most advantageous due to its low on resistance.Unfortunately,the gate drive difficulties make it less than ideal in applicaitons and as a resu
6、lt there are few NMOS LDOs available.传统上，PNP 双极型晶体管应用到低压线性稳压器，主要是因为它很容易实现了低压降电压。2 Traditionally,the PNP bipolar transistor has been applied to low dropout applications,primarily because it easily enables a low drop out voltage.However,it has a high quiescent current and low efficiency，which are not
7、ideal in applications where maximizing efficiency is a priority。然而，它的高静态电流和低效率，这是不理想的应用最大限度地提高了效率是一个优先事项。3 PMOS devices have been highly developed and now have performance levels exceeding most bipolar devices.PMOS 上设备已经高度发达，现在的性能水平超过最双极器件.Dropout voltage：the inputtooutput differential voltage at wh
8、ich the circuit ceases to regulate against further reductions in input voltage;this point occurs when the input voltage approaches the output voltage。压降：对输入至输出差分电压在电路不再规范对进一步削减输入电压;这一点时发生的输入电压接近输出电压.Vds=VoVin IC基本电气特性Efficiency The efficiency of a LDO regulator is limited by the quiescent current an
9、d input/output voltage as follows:效率是有限的 LDO 稳压器的静态电流和输入/输出电压如下：输入电压降低；这一点时发生的输入电压接近输出电压。To have a high efficiency LDO regulator,drop out voltage and quiescent current must be minimized.具有高效率的 LDO 稳压器，电压和辍学静态电流必须减少到最低限度 IC基本电气特性Load Regulation Load Regulation：A measure of the circuits ability to mai
10、ntain the specified output voltage under varying load conditions。衡量电路的能力,保持指定的输出电压在不同负载条件下。The load regulation is limited by the open loop current gain of the system.As noted from the above equation,increasing dc openloop current gain improves load regulation.负荷调节是有限的开环电流增益的系统.正如上述方程,增加直流开环电流增益改善负载调
11、节。100oooqiI VEfficiencyIIV_miniodropVVV/VoIo Line Regulation:a measure of the circuits ability to maintain the specified output voltage with varying input voltage.衡量这条赛道的能力，保持指定的输出电 voltage.open 环电流增益改善负载调节。其中，Rds 为调整管 Q1 源漏等效电阻。Increasing dc open loop current gain improves the line regulation.提高直流开
12、环电流增益提高了线路调整 /VoVi Output Voltage With Respect to Input Voltage Line Transient Response IC基本电气特性Transient Response Transient Response：the maximum allowable output voltage variation for a load current(input voltage)step change。瞬态响应:允许的最大输出电压变化的负载电流（输入电压)一步变化。The transient response is a function of th
13、e output capacitor value（Co),the ESR of the output capacitor，the buypass capacitor(Cb），and the maximum load-current（Io，max）。瞬态响应是一个功能的输出电容值（公司）中，电子自旋共振的输出电容器,电容 器 的buypass(炭黑），最大负载电流(Io，最大值).Where t1 corresponds to the closed loop bandwidth。ESR is the voltage variation resulting from the presence of
14、 the ESR of the output capacitor。ESR is proportional to ESR.凡 t1 闭环带宽.esr 是电压变化造成在场的情况下的 ESR 的输出电容器。esr 成正比 esr。Transient Response of LDO Regulator瞬态响应 LDO 稳压器 输出电容的影响 ESL loadtransient response负载瞬态响应 ESR load-transient response ESL 影响比较小，但不合适的 PCB 布线同样使得性能下降。ESR 是越小越好,但 成本稳定性 IC基本电气特性 Power Supply
15、Rejection PSRR:also known as ripple rejection,measures the LDO regulators ability to prevent the regulated output voltage fluctuating caused by input voltage variations.也被称为纹波抑制，措施的 LDO 稳压器的能力，以防止输出电压波动所造成的输入电压的变化 The same relation for line regulation applies to PSRR except that the whole frequency
16、spectrum is considered.同样的关系线适用于的 PSRR，但整个频谱是考虑.PSRR is based on small signals，whereas line transients are large signals。PSRR是基于小信号，而电压瞬态大信号。Very critical in many RF and wireless application非常关键的在许多射频和无线应用 supply rejection in the frequency band between 100 kHz and 1 MHz is especially important in ap
17、plications where the output of a dc/dc switch mode power supply(SMPS)is used to power the linear regulator抑制频带在 100 kHz 和 1 MHz 的是特别重要的应用场合中的输出的 DC/DC 开关模式电源(SMPS）是用于功率的线性稳压器 But why battery-powered application?application？?But why batterypowered The output voltage will show a large variation based
18、upon the current drawn from that battery.输出电压将出现大的变化根据目前从该电池。In GSM，transmit and receive cycles in the RF draw a huge amount of current，causing a large change in voltage on the output of the battery。That change in voltage is seen throughout the system and on inputs to all of the system regulators.在
19、GSM，传输和接收周期中的射频吸引了大量的电流,造成一个大的变化对输出电压的电池。这一变化在电压是整个系统，并投入到所有的系统监管。One of the dominant internal sources of PSRR in an LDO is the bandgap reference。so its important to have a bandgap reference with high PSRR.其中一个主要的内部来源的PSRR 的 LDO 中的带隙基准。因此，必须有一个带隙基准高的 PSRR。Board layout must be carefully done to reduc
20、e the feedthrough from input to output via board parasitics。电路板布局必须认真进行，以减少馈从输入输出通过董事会寄生。Improved Power Supply Rejection For IC Linear Regulators LC filter滤波器 IC基本电气特性 Noise 在输出信号中包含我们不需要的信号.PSRR、NOISE 容易混淆的概念！PSRR 输入变化引起输出的变化，抑制能力 NOISE固有特性，和外部无关,主要由芯片内部电阻、晶体管产生。衡量 NOISE 的两种式：Spectral谱线 noise densi
21、ty密度 a curve 曲线that shows noise(uV/Hz)versus 相对 Equipment设备:frequency频率，that is，noise spectral density cure spectrum analyzer光谱分析器。with units uV/Hz plotted over frequency Integrated综合的 output noise spectral noise density integrated over a output noise voltage(in Vrms)certainfrequency range and can t
22、herefore be thought of as the total noise in a specified frequency range。Equipment:True rootmean-square（Rms）meter Absolute measurement with units uVRMS（root mean square）take over a fixed bandwidth 真有效值测量 AC/DC ，噪声源:Reference 重要因素，通过外接 LPF 来减小基准噪声的影响.但电容也不能太大，否则会对启动产生影响。LPF 的 CUTOFF 频率一般会设在 1500KHz r
23、esistor divider电阻分割器 热噪声 4KTR，要减小噪声，采样电阻的阻值不能取很大.和低功耗要求相矛盾,如果噪声是必须考虑的因素，也只有部分的牺牲功耗.EA 若是 2 级运放，则低噪声设计，第一级提供大部分的GAIN.PASS FET 调整管虽然占芯片比较大的面积,对 NOISE 的影响不大，因为和其它几个因素相比，PASS FET 缺少了增益级。整个环路的频率特性也会对 NOISE 产生影响.相位裕度减小,环路趋于不稳定，增益的峰值变大。output noise voltage（in Vrms)是对频域的噪声做积分，噪声的增益大了，所以噪声也会大。所以对于低噪声的设计，尽量采用
24、大的相位裕度。如果可以的话可以在R1两端并一个小电容,这样在高频时,基准到输出之间是一个单位增益的放大器.IC基本电气特性 Accuracy准确性 Accuracy：specifies all effects of line regulation（VLR）,load regulation(VLDR）,reference voltage drift（Vo,ref)，error amplifier voltage drift（Vo,a)，external sampling resistor tolerance(Vo,r）,and temperature coefficient(VTC）。指定所有影响线路调整，负载调节，参考电压漂移，误差放大器电压漂移，外部取样电阻宽容，和温度系数.