Michael Peters， Senior Applications Engineer

Michael Peters，高级应用工程师

This is the first article in a 2－part series． Part 1 introduces the digital power system manager （DPSM） family and covers the primary methods of current sensing． LTpowerPlay? is also introduced， and energy metering described． Part 2 covers current sensing on high voltage or negative supplies， accuracy， and highlights the digital aspects of the DSPM family．

本系列文章分为两部分，这是第一部分。第一部分介绍数字电源系统管理器（DPSM）系列，并说明电流检测的主要方法。另外还会介绍LTpowerPlay?并讨论电能计量。第二部分探讨高压或负电源上的电流检测及精度，并重点介绍DSPM系列的数字方面。

Introduction

简介

Board level designers are tasked with giving life to a board， monitoring its health， adjusting settings， running diagnostics， bringing it offline for inspection， trouble－shooting when things are not quite right， and gracefully powering down a complex board without incident． In the world of designing and developing power supplies， power management may not only be desirable， but a hard requirement． The power system manager aggregates a variety of functions， such as power－on sequencing， detecting faults， margin testing， coordinating shutdown， measuring voltages， measuring currents， and collecting data for analysis． Measuring supply current with LTC297x devices is the focus of this article．1

电路板级设计人员的任务是赋予电路板以生命，监视其健康状况，调整设置，运行诊断，脱机进行检查，在出现问题时排除故障，以及在无事故的情况下有序地关断复杂的电路板。在电源设计和开发的世界里，电源管理可能不仅仅是一种需要，更是一项硬性要求。电源系统管理器聚合了多种功能，例如上电时序管理、故障检测、裕量测试、协调关断、测量电压、测量电流以及收集数据进行分析。使用LTC297x器件测量电源电流是本文的重点1。

For supplies that power high value components， such as FPGAs， CPUs， and optical transceivers， it may be important to measure the current drawn from the supply rail． For these critical supply rails， this data allows the board designer to gain insight into its performance． When current is measured and the current value is in a digital format， the device can compute power and energy， and the system host can perform unique calculations， look for trends in the data， schedule tasks， etc．

对于为FPGA、CPU、光收发器等高价值器件供电的电源，测量其从电源轨汲取的电流可能很重要。对于这些关键电源轨，电路板设计人员可以通过此数据深入了解其性能。当电流信息被测量到，且电流值为数字格式，那么器件就可以计算功率和电能，系统主机也可以执行独特的计算、从数据中分析趋势、安排任务等。

Many technical articles and application notes are written on the topic of sensing current， but none have covered the topic specifically for DPSMs． This article covers both the analog and digital aspects and describes various supporting circuits for measuring current of low voltage， high voltage， and negative rails．

围绕电流检测这一主题已有许多技术文章和应用笔记问世，但没有一篇是专门针对DPSM的。本文涵盖了模拟和数字方面，并描述了用于测量低压、高压和负电源轨的各种支持电路。

The LTC297x DPSM Family

LTC297x DPSM系列

The focus of this article is power system managers that have built－in current measurement． Table 1 describes the differences between these devices．

本文的重点是内置电流测量功能的电源系统管理器。表1说明了这些器件之间的差异。

The LTC2977／LTC2979／LTC2980／LTM2987 can be configured to monitor current， but there are some limitations． Only odd－numbered channels support current measurement， and measurements are returned in unscaled units of volts． This is covered in more detail in Part 2．

LTC2977／LTC2979／LTC2980／LTM2987可配置用来监视电流，但存在一些限制。只有奇数通道支持电流测量，并且测量值以未缩放的单位（V）返回。这在第二部分中有更详细的介绍。

This article focuses on the LTC2971／LTC2972／LTC2974／LTC2975 devices due to their ability to measure output current and allow the system／software to read back values in units of amps using the READ＿IOUT command．

本文重点介绍LTC2971／LTC2972／LTC2974／LTC2975器件，它们能够测量输出电流，并允许系统／软件利用READ＿IOUT命令回读以安培（A）为单位的值。

Note AN105： Current Sense Circuit Collection Making Sense of Current covers a wide variety of circuits and scenarios． A portion of this collection applies to the ADI digital power system managers．

应用笔记AN105：帮助弄懂电流的电流检测电路集合介绍了广泛的电路和使用场景。该集合的一部分适用于ADI数字电源系统管理器。

Table 1． Family of LTC297x DPSM Devices

表1．LTC297x DPSM器件系列

1 Unless otherwise specified， the term LTC297x in this application note refers to the LTC2971， LTC2972， LTC2974， LTC2975， LTC2977， LTC2979， LTC2980， and LTM2987． It does not include the LTC2970．

除非另有说明，本应用笔记中的LTC297x指LTC2971、LTC2972、LTC2974、LTC2975、LTC2977、LTC2979、LTC2980和LTM2987，而不包括LTC2970。

PSM Basics

PSM基础

Power system managers provide a digital view of key voltage and current readings of a power supply． This is a powerful feature of the product family： a system host or LTpowerPlay can support initial board bring up， debugging， validating or collecting baseline data， or looking for trends． While some power supply channels do not require accurate current readings， many critical output channels need highly accurate current measurements．

电源系统管理器提供关于电源的关键电压和电流读数的数字视图。这是该产品系列的一个强大特性：系统主机或LTpowerPlay可以支持电路板初始启动、调试、验证或收集基线数据，或者寻找趋势。虽然一些电源通道不需要精确的电流读数，但许多关键的输出通道需要高度精确的电流测量。

Various current sense options will be covered in this article， including trade－offs between cost， complexity， and accuracy．

本文将介绍各种电流检测选项，包括成本、复杂性和精度之间的权衡。

Figure 1． READ＿IOUT telemetry plot in LTpowerPlay．

图1．LTpowerPlay中的READ＿IOUT遥测曲线

Current Sensing Options

电流检测选项

The LTC2971／LTC2972／LTC2974／LTC2975 managers accurately measure output current． Use these devices when possible because they have dedicated current sense pins and PMBus commands that provide telemetry values in amps．

LTC2971／LTC2972／LTC2974／LTC2975管理器能够精确测量输出电流。应尽可能使用这些器件，因为它们具有专用的电流检测引脚和PMBus命令，可提供以安培为单位的遥测值。

Figure 2． Current sensing with series shunt．

图2．使用串联分流器进行电流检测

For example， wire the ISENSE lines to a shunt， configure a few registers， and the chip does the rest． The chip converts a measured sense voltage to a current value． LTpowerPlay displays the current in real time as numerical values and in a telemetry plot．

例如，将ISENSE线连接到分流器，配置几个寄存器，剩下的工作由芯片完成。芯片会将测得的电压转换为电流值。LTpowerPlay将电流实时显示为数值和遥测曲线。

Figure 3． PMBus register settings for output current measurement．

图3．用于输出电流测量的PMBus寄存器设置

It is also possible to use an LTC2977／LTC2979／LTC2980／LTM2987 to measure output current； however， the READ＿IOUT command returns a voltage that must be converted to amps by the system host or LTpowerPlay． In practice， this means the firmware， rather than the chip， must store the value of the series shunt．

也可以使用LTC2977／LTC2979／LTC2980／LTM2987来测量输出电流，但是，READ＿IOUT命令返回的是电压，必须由系统主机或LTpowerPlay将其转换为安培。实践中，这意味着固件（而不是芯片）必须存储串联分流器的值。

A series shunt resistor is not the only way to sense current． Table 2 summarizes the current sensing options available for the DPSM family and their trade－offs． Accuracy， cost， board space， and other factors also need to be considered．

串联分流电阻并非检测电流的唯一方法。表2总结了DPSM系列可用的电流检测选项及其权衡。精度、成本、电路板空间和其他因素也需要考虑。

Table 2． Summary of Current Sense Options

表2．电流检测选项总结

Shunt Resistor Sensing

分流电阻检测

The most common sensing method uses a shunt resistor， sometimes called a current shunt． Whether the DC－to－DC converter is a switching regulator or linear regulator， the shunt resistor is placed in series with the output． The feedback resistor divider is connected to the output node such that the shunt is inside the feedback loop， which allows the regulator to compensate for the shunt resistor’s IR drop when load current is applied， significantly improving the load regulation．

最常见的检测方法是使用分流电阻，有时也称为检流电阻。无论DC－DC转换器是开关稳压器还是线性稳压器，分流电阻都与输出串联。反馈电阻分压器连接到输出节点，使得分流器位于反馈环路内，这样当施加负载电流时，稳压器就能补偿分流电阻的IR压降，从而显著提高负载调整率。

Figure 4． Sense resistor inside the feedback loop．

图4．反馈回路内的检测电阻

The PMBus command used to convert voltage to current is called IOUT＿CAL＿GAIN． This is the nominal resistance of the shunt resistor． The chip measures the small voltage drop across the shunt resistor via the ISENSE pins， performs the conversion internally， and returns the output current with the READ＿IOUT command． The actual voltage that is sensed by the chip is available using the MFR＿IOUT＿SENSE＿VOLTAGE command． The chip computes the output current with this equation：

用于将电压转换为电流的PMBus命令称为IOUT＿CAL＿GAIN。这是分流电阻的标称电阻。芯片通过ISENSE引脚测量分流电阻上的小电压降，在内部执行转换，并使用READ＿IOUT命令返回输出电流。芯片检测到的实际电压可通过MFR＿IOUT＿SENSE＿VOLTAGE命令获得。芯片使用以下公式计算输出电流：

When using a resistive shunt， set the MFR＿IOUT＿CAL＿GAIN＿TC value to the manufacturer’s specifications to compensate for temperature changes． Generally， shunts greater than 10 m? have lower temperature coefficients： ＜100 ppm／°C．

使用阻性分流器时，将MFR＿IOUT＿CAL＿GAIN＿TC值设置为制造商的规格以补偿温度变化。通常，大于10 mΩ的分流器具有较低的温度系数：＜100 ppm／°C。

The maximum differential sense voltage developed across the ISENSE pins is listed in the data sheet specifications． Most of the LTC297x devices are limited to ±170 mV of differential voltage． This provides more than enough range for the majority of applications． The max sense voltage is calculated as follows： VSENSE ＝ RSNS × IOUT（MAX）． Generally， the max sense voltage is determined first and the RSNS current sense resistor is calculated as follows： RSNS ＝ VSENSE ／ IOUT（MAX）． The max sense voltage is chosen to be a large enough signal， yet not create a power dissipation problem or IR drop in the output path． 50 mV to 80 mV is a good max sense voltage． Select a current sense resistor’s physical size so that it provides a power dissipation rating greater than the calculated power dissipation in the sense resistor： PD ＝ RSNS × （IOUT（MAX））2．

数据手册规格中列出了ISENSE引脚上产生的最大差分检测电压。大多数LTC297x器件的差分电压以±170 mV为限，这为大多数应用提供了足够的范围。最大检测电压计算如下：VSENSE ＝ RSNS × IOUT（MAX）。通常，首先确定最大检测电压，RSNS电流检测电阻计算如下：RSNS ＝ VSENSE ／ IOUT（MAX）。选择的最大检测电压应是一个足够大的信号，但又不会在输出路径中造成功耗问题或IR压降。50 mV至80 mV是一个很好的最大检测电压。选择电流检测电阻的物理尺寸，其功耗额定值应大于检测电阻的计算功耗：PD ＝ RSNS × （IOUT（MAX））2。

A related method adds a ground referenced current sense amplifier （CSA） to provide a single－ended output that is fed into the current sense pins of the manager． This approach is typically used for level translating a rail that is higher than the 6 V limit of most LTC297x managers． The CSA should have good high－side common－mode performance． It is typical to power such a device from the sensed rail and GND． Details on this method are covered in Part 2 of this article．

一种相关方法是增加一个以地为基准的电流检测放大器（CSA），其提供单端输出，该输出被馈送到管理器的电流检测引脚。这种方法通常用于对高于大多数LTC297x管理器的6 V限值的电压轨进行电平转换。CSA应具有良好的高端共模性能。通常从被检测的电压轨和GND为此类器件供电。本文第二部分会详细介绍这种方法。

Figure 5． Current sense amplifier used for higher voltage rails．

图5．用于更高电压轨的电流检测放大器

ADI offers many easy to use non－PSM μModule? devices with a small footprint． A PSM manager is a good companion device to control sequencing and supervise them． Most μModule devices have internal inductors． However， some also integrate the topside feedback resistor， making it impossible to add an external shunt resistor inside the feedback loop． One should select a μModule device that allows the use of an external topside feedback resistor for the highest voltage accuracy．

ADI公司提供了许多易于使用且小尺寸的非PSM μModule?器件。PSM管理器是很好的配套器件，可控制上电时序并实施监控。大多数μModule器件都有内置电感，但有些还集成了上方反馈电阻，因此无法在反馈环路内添加外部分流电阻。应当选择允许使用外部上方反馈电阻以获得最高电压精度的μModule器件。

Inductor DCR Sensing

电感DCR检测

DCR sensing is the method that senses current through a buck regulator’s output inductor． An inductor can be modeled as an ideal inductance and a series resistance called DCR （see Figure 6）． This is typically the preferred method for high current （＞20 A） rails． The addition of a resistive shunt is an extra component， which dissipates power and generates heat．

DCR检测是一种通过降压稳压器的输出电感检测电流的方法。电感可以用理想电感和一个称为DCR的串联电阻来建模（见图6）。这通常是高电流（＞20 A）电源轨的首选方法。增加的阻性分流器是一个额外的元件，会消耗功率并产生热量。

One must have access to both ends of the inductor to sense across it， and a filter network must be inserted between the sense points and the LTC297x sense pins． The filter network is a 2－stage differential RC low－pass filter． For convenience and small footprint， a 4－element resistor array can be used． The resistor values should be chosen such that the IR drop is small enough to prevent errors from the LTC297x input current， yet large enough to keep the capacitor values less than 1 μF．

要在电感上进行检测，必须能够接触到电感的两端，并且必须在检测点和LTC297x检测引脚之间插入一个滤波器网络。滤波器网络是一个两级差分RC低通滤波器。为了方便和减小尺寸，可以使用4元件电阻阵列。电阻值的选择应使IR压降足够小，以防止LTC297x输入电流造成误差，同时又足够大，以使电容值小于1 μF。

The LTC2971／LTC2972／LTC2974／LTC2975 data sheets provide guidance for selecting RC values．

LTC2971／LTC2972／LTC2974／LTC2975数据手册提供了关于选择RC值的指南。

Example：

示例：

Assume L ＝ 2．2 μH， DCR ＝ 10 m?， fSW ＝ 500 kHz

假设L ＝ 2．2 μH，DCR ＝ 10 mΩ，fSW ＝ 500 kHz

Let Rcm1 ＝ Rcm2 ＝ 1 kΩ

令Rcm1 ＝ Rcm2 ＝ 1 kΩ

Figure 6． DCR inductor sensing with a 2－pole low－pass filter．

图6．使用2极点低通滤波器的DCR电感检测

DCR sensing offers a lossless measurement of current； however， the accuracy suffers due to variability of inductor winding resistance or DCR． It is not uncommon to see inductor DCR specifications as much as ±10％ or only a maximum value． The actual DCR value will vary from inductor to inductor， and from lot to lot．

DCR检测可实现电流的无损测量，但由于电感绕组电阻或DCR的差异，精度会受到影响。电感DCR规格高达±10％或只有一个最大值的情况并不少见。实际的DCR值会因电感和批次而异。

An alternative filtering scheme uses only two resistors and two capacitors． This reduces the component count from eight down to four； however， the filter performance is not as good as in Figure 7．

另一种滤波方案仅使用两个电阻和两个电容，因而元件数量从八个减少到四个，但滤波器的性能不如图7所示的好。

Figure 7． DCR inductor sensing with a simplified low－pass filter．

图7．使用简化低通滤波器的DCR电感检测

PMBus Configuration

PMBus配置

To configure the LTC297x using PMBus commands， the nominal value for the shunt resistor or inductor DCR is set using the IOUT＿CAL＿GAIN command． For inductors wound with copper wire， the DCR increases as inductor temperature increases． This will introduce errors in the READ＿IOUT reading． This can be compensated for by setting the copper’s temperature coefficient with the MFR＿IOUT＿CAL＿GAIN＿TC command． The data sheet default for this value is 3900 ppm／°C． You may need to adjust the value to match your inductor， because this parameter can vary widely when the wire is an alloy， not pure copper． MFR＿IOUT＿CAL＿GAIN＿THETA is the thermal time constant that may be set． The LTC297x data sheets cover these in more detail．

要利用PMBus命令配置LTC297x，可使用IOUT＿CAL＿GAIN命令设置分流电阻或电感DCR的标称值。对于铜线缠绕的电感，DCR会随着电感温度升高而增加，这会在READ＿IOUT读数中引入误差。使用MFR＿IOUT＿CAL＿GAIN＿TC命令设置铜的温度系数可补偿此误差。在数据手册中，该值的默认值为3900 ppm／°C。用户可能需要调整该值以匹配电感，因为当导线是合金而非纯铜时，此参数可能会大幅改变。MFR＿IOUT＿CAL＿GAIN＿THETA表示热时间常数，可对其进行设置。LTC297x数据手册详细介绍了这些内容。

It is important to place a temperature sensor （diode－connected bipolar transistor） close to the inductor to achieve a more accurate current temperature compensation． The LTC2971／LTC2972／LTC2974／LTC2975 devices have TSENSE pins that are connected to the sensor．

必须将温度传感器（二极管连接的双极性晶体管）靠近电感放置，以实现更准确的电流温度补偿。LTC2971／LTC2972／LTC2974／LTC2975器件具有连接到传感器的TSENSE引脚。

IMON

IMON

IMON pins are gaining popularity in many regulators， both switching and linear． These regulators have a current sense output pin that provides a means of monitoring the regulator’s load current． The advantages of the IMON method are that it is lossless and there is no common－mode voltage to worry about because the LTC297x ISENSE pins do not connect to VOUT． The IMON pin is a single－ended output signal that represents a fraction of the output current， and it can be either a voltage output or a current output， which requires a resistor connected to GND． Current output IMON pins allow the user to select a resistor value， and hence set the maximum full load voltage．

IMON引脚在许多稳压器（包括开关和线性）中越来越受欢迎。这些稳压器有一个电流检测输出引脚，藉此可监视稳压器的负载电流。IMON方法的优点在于它是无损的，并且无需担心共模电压，因为LTC297x ISENSE引脚不连接到VOUT。IMON引脚是单端输出信号，代表输出电流的一小部分，它可以是电压输出或电流输出，需要一个电阻连接到GND。电流输出IMON引脚允许用户选择电阻值，从而设置最大满载电压。

A single－ended voltage can be a much larger signal than a voltage developed across a current shunt or inductor DCR． The LTC2972 and LTC2971 devices even have a configuration bit to allow larger signal levels． It is called the imon＿sense bit． The bit is located in the MFR＿CONFIG command and is a paged command．

单端电压可以是比电流分流器或电感DCR两端产生的电压大得多的信号。LTC2972和LTC2971器件甚至有一个配置位来支持更大的信号电平，它被称为imon＿sense位。该位位于MFR＿CONFIG命令中，是一个分页命令。

Figure 8． IMON bit in the MFR＿CONFIG register．

图8．MFR＿CONFIG寄存器中的IMON位

The IMON resistor value should be chosen to allow wide dynamic range under all load conditions． In general， IMON accuracy is good under medium and heavy load current conditions but loses accuracy under light loads． Check the regulator’s data sheet specifications for more details．

选择的IMON电阻值应使得在所有负载条件下都能提供宽动态范围。一般情况下，IMON精度在中负载和重负载电流条件下较好，但在轻负载下会下降。有关更多详细信息，请查阅稳压器的数据手册规格。

Figure 9． PSM measures current with IMON．

图9．PSM利用IMON测量电流

Some regulators combine a current limit function with the IMON pin． The pin may be called IMON／ILIM． Be careful not to select an IMON resistor value such that the IMON voltage activates the current limit circuit under full load． Examples include linear regulators， such as the LT3072 and LT3086． In other cases， such as the LT3094 and LT3045， there is an ILIM pin that functions as a current limit and may be used as an output current monitor． In the case of some switching regulators， the pin may be called IMON and a built－in current limit function may not be obvious． Examples include the LT8652S and LT8708． The current limit circuit has a foldback and does not shut down the output． To shut off the output， an LTC298x will detect an overcurrent condition and pull VOUT＿EN low， disabling the regulator’s output．

一些稳压器将限流功能与IMON引脚结合在一起，该引脚可称为IMON／ILIM。请注意，所选的IMON电阻值不应使得IMON电压在满载时会激活限流电路。示例包括线性稳压器，例如LT3072和LT3086。其他例子有LT3094和LT3045等，一个ILIM引脚起到限流作用，可用作输出电流监视器。对于某些开关稳压器，该引脚可称为IMON，内置的限流功能可能并不明显。示例包括LT8652S和LT8708。限流电路具有折返功能，不会关闭输出。若要关闭输出，LTC298x会检测过流状况并将VOUT＿EN拉低，从而禁用稳压器输出。

Input Current Sensing

输入电流检测

A power system may have a single input supply that powers a number of down－stream regulators． The input supply current may be measured by an LTC2971， LTC2972， or LTC2975． It is straightforward to measure IIN with the LTC2971／ LTC2972／LTC2975， as these devices have native capability to connect pins to a sense resistor RSNS in the current path of VIN． Direct wiring of the IIN＿SNS pins is limited to VIN supplies that are ＜15 V for the LTC2972／LTC2975， and ＜60 V for the LTC2971．

一个电源系统可能有一个输入电源，其为多个下游稳压器供电。输入电源电流可由LTC2971、LTC2972或LTC2975进行测量。使用LTC2971／LTC2972／LTC2975测量IIN非常简单，因为这些器件原本就有将引脚连接到VIN电流路径中的检测电阻RSNS的能力。IIN＿SNS引脚的直接接线以VIN电源为限，对于LTC2972／LTC2975而言，该值＜15V；对于LTC2971而言，该值＜60V。

Figure 10． VIN current and voltage sensing．

图10．VIN电流和电压检测

Whether measuring output current or input supply current， there is a user－programmable PMBus register that translates the sense voltage to a current． In the case of input supply current， the PMBus register MFR＿IIN＿CAL＿GAIN is used． The input supply current can then be read from the READ＿IIN register．

无论是测量输出电流还是输入电源电流，都有一个用户可编程PMBus寄存器可将检测电压转换为电流。测量输入电源电流时，使用PMBus寄存器MFR＿IIN＿CAL＿GAIN，然后便可从READ＿IIN寄存器读取输入电源电流。

Figure 11． PMBus registers for VIN current measurement．

图11．用于VIN电流测量的PMBus寄存器

We can measure not only the current but the voltage as well． The PMBus commands are READ＿IIN and READ＿VIN． With current， voltage， and a time base， the LTC2971／LTC2972／LTC2975 can also compute power and energy delivered to the system． The energy accumulator is described in the next section．

我们不仅可以测量电流，还可以测量电压。PMBus命令分别为READ＿IIN和READ＿VIN。利用电流、电压和时基，LTC2971／LTC2972／LTC2975还能计算输送给系统的功率和电能。蓄能器将在下一节中描述。

The LTC2971 is capable of sensing input supply current on a 60 V rail． The IIN＿SNS pins may be directly connected to a sense resistor on the supply’s input． For supply voltages above 24 V， we recommend using a buck regulator to power the LTC2971 via the VPWR pin． This saves power and avoids self－heating the LTC2971． Power is dissipated due to VPWR × IPWR and can cause the die temperature to increase higher than desired． The ADP2360 has a fixed 5 V option that offers a low cost， small footprint solution for the buck regulator．

LTC2971能够检测60V电源轨上的输入电源电流。IIN＿SNS引脚可以直接连到电源输入上的检测电阻。对于24V以上的电源电压，建议使用降压稳压器通过VPWR引脚为LTC2971供电，这样可节省功率并避免LTC2971自发热。由于VPWR × IPWR会产生功耗，可能导致芯片温度升高到预期以上。ADP2360具有一个固定5 V选项，可为降压稳压器提供低成本、小尺寸的解决方案。

Figure 12． High voltage VIN current and voltage sensing with the LTC2971．

图12．使用LTC2971检测高压VIN电流和电压

Energy Metering

电能计量

It may be important that the energy usage be monitored． Whether the input supply is a switching regulator， solar panel output， or battery source， it may be useful to know the total energy consumed by the system． The LTC2971／LTC2972／ LTC2975 are capable of high－side current sensing of the input power supply． This feature allows the manager to measure input supply current． LTpowerPlay is very useful for exploring the features related to input supply current and energy reading． Once you select the READ＿EIN command， the telemetry window will display a real－time plot of energy accumulated．

监视电能使用可能很重要。无论输入电源是开关稳压器、太阳能电池板输出还是电池电源，了解系统消耗的总电能可能很有用。LTC2971／LTC2972／LTC2975能够检测输入电源的高端电流。此特性允许管理器测量输入电源电流。LTpowerPlay对于探索与输入电源电流和电能读数相关的特性非常有用。选择READ＿EIN命令后，遥测窗口就会显示电能累计结果的实时曲线。

Figure 13． Real－time energy plot from LTpowerPlay．

图13．LTpowerPlay绘制的实时电能图

The energy meter also measures input supply voltage and is therefore able to report input power as well． Since energy is the product of power and time， accumulated energy is provided based on the manager’s internal time base． The meter displayed in the upper right－hand corner of the GUI provides more information． The needle is a real－time indicator of input power in watts， and the smaller five dials show the total accumulated energy similar to a home electricity meter． Digital readouts are also provided for convenience．

电表还会测量输入电源电压，因此也能够报告输入功率。由于电能是功率和时间的乘积，因此累计电能是根据管理器的内部时基提供的。GUI右上角显示的仪表提供了更多信息。指针是输入功率（以瓦特为单位）的实时指示器，较小的五个刻度盘显示总累计电能，类似于家用电表。为方便起见，还提供了数字读数。

Figure 14． Energy meter in LTpowerPlay．

图14．LTpowerPlay中的电表

LTpowerPlay offers a simple and easy to understand interface that brings together input and output current， voltage， power， and energy readings．

LTpowerPlay提供一个简单易懂的界面，其中汇集了输入和输出电流、电压、功率、电能读数。

Input current， input voltage， input power， and input energy may be viewed in tabular format． These appear in the telemetry portion of the GUI． The MFR＿EIN register holds the accumulated energy value in millijoules． There is also a total time that the energy accumulator has been active and is shown as the MFR＿EIN＿ TIME register． The GUI will automatically update the displayed SI prefix as the units change from mJ to J to kJ．

输入电流、输入电压、输入功率和输入电能可以表格形式查看，这些值显示在GUI的遥测部分。MFR＿EIN寄存器保存累计电能值（以毫焦耳为单位）。还有一个电能累计器处于活动状态的总时间，显示为MFR＿EIN＿TIME寄存器。当单位从mJ变为J再到kJ时，GUI会自动更新所显示的SI前缀。

Figure 15． View of telemetry related to input supply voltage， current， power， and energy．

图15．与输入电源电压、电流、功率和电能相关的遥测视图

Table 3 is a summary of all telemetry that can be read back from the LTC297x． The registers are I2C／PMBus word reads except for the MFR＿EIN register， which is a block read．

表3总结了可以从LTC297x回读的所有遥测数据。寄存器是I2C／PMBus字读取，但MFR＿EIN寄存器除外，它是块读取。

Table 3． Summary of Telemetry

表3．遥测总结

1． If the adc＿hires bit is set， READ＿VOUT value is returned in mV． L11 format．

如果设置了adc＿hires位，则READ＿VOUT值以mV为单位返回。L11格式。

2． Block read that includes energy value in mJ and elapsed time in ms．

块读取，包括以mJ为单位的电能值和以ms为单位的经过时间。

About the Author

作者简介

Michael Peters is a senior applications engineer for power system management devices at Analog Devices． He has more than 30 years of experience in analog and digital circuits， including working on memory devices at previous companies． He received his B．S．E．E． degree from the University of Michigan， Ann Arbor， Michigan． He can be reached at michael．peters＠analog．com．

Michael Peters是ADI公司电源系统管理器件方面的高级应用工程师。他在模拟和数字电路领域拥有30多年的经验，包括在以前的公司从事存储器件工作的经验。他毕业于密歇根大学安娜堡分校，获电气工程学士学位。联系方式：michael．peters＠analog．com。