美国国家半导体公司（National Semiconductor Corp.）（美国纽约证券交易所上市代码：NSM）宣布推出两款可配置的传感器模拟前端（AFE）集成电路，两款产品采用美国国家半导体的独创技术，并获得多款全新设计工具的支持，令系统设计工程师可以使用各大厂商生产的各类传感器产品完成信号路径设计，将产品快速推向市场。

    NS公司的LMP90100是传感器模拟前端（AFE）系统，是多路低功耗24位的传感器AFE,具有精密的24位Sigma-Delta ADC和低噪音可编增益放大器（1x - 128x）和全差分高阻抗模拟输入复接器。ENOB/NFR高达21.5/19位，失调误差8.4nV,增益误差7ppm,总噪音小于10 μV-rms,输出数据速率（ODR）为1.6775 SPS - 214.65 SPS,主要用在温度和压力发送器，应力仪接口和工业过程控制。本文介绍LMP90100主要特性和指标， 方框图，多种典型应用和配置电路， LMP90100EB评估板电路图和材料清单。

    LMP90100:Sensor AFE System: Multi-Channel, Low Power 24-Bit Sensor AFE with True Continuous Background Calibration

    The LMP90100 is a highly integrated, multi-channel, low power 24-bit Sensor AFE. The device features a precision, 24-bit Sigma Delta Analog-to-Digital Converter （ADC） with a low noise programmable gain amplifier and a fully differential high impedance analog input multiplexer. A true continuous background calibration feature allows calibration at all gains and sample rates without interrupting the signal path. The background calibration feature essentially eliminates gain and offset errors across temperature and time, providing measurement accuracy without sacrificing speed and power consumption.

    Another feature of the LMP90100 is continuous background sensor diagnostics, allowing the detection of open and short circuit conditions and out-of-range signals, without requiring user intervention, resulting in enhanced system reliability.

    Two sets of independent external reference voltage pins allow multiple ratiometric measurements. In addition, two matched programmable current sources are available to excite external sensors such as resistive temperature detectors and bridge sensors. Furthermore, seven GPIO pins are provided for interfacing to external LEDs and switches to simplify control across an isolation barrier.

    Collectively, these features make the LMP90100 a complete analog front-end for low power, precision sensor applications such as temperature, pressure, strain gauge, and industrial process control. The LMP90100 is guaranteed over the extended temperature range of -40℃ to +105℃ and is available in a 28-pin TSSOP package.

    LMP90100主要特性:
    ■ 24-Bit Low Power Sigma Delta ADC
    ■ True Continuous Background Calibration at all gains
    ■ Low-Noise programmable gain (1x - 128x)
    ■ Continuous background open/short and out of range sensor diagnostics
    ■ 8 selectable output data rates (ODR) with single-cycle settling
    ■ 2 matched excitation current sources from 100 μA to 1000 μA
    ■ 4-DIFF / 7-SE flexible and programmable MUX channels
    ■ 7 General Purpose Input/Output pins
    ■ Chopper-stabilized buffer for low offset
    ■ SPI 4 wire serial interface with CRC data link error correction
    ■ Simultaneous 50 Hz & 60 Hz line rejection at ODR ≤13.42 SPS
    ■ Independent gain and ODR selection per channel
    ■ Supported by Webench Sensor AFE Designer
    ■ Automatic Channel Sequencer
    LMP90100主要指标:
    ■ ENOB/NFR Up to 21.5/19 bits
    ■ Offset Error (typ) 8.4 nV
    ■ Gain Error (typ) 7 ppm
    ■ Total Noise < 10 μV-rms
    ■ Integral Non-Linearity (INL max) ±15 ppm of FSR
    ■ Output Data Rates (ODR) 1.6775 SPS - 214.65 SPS
    ■ Analog Voltage, VA +2.85V to +5.5V
    ■ Digital Input/Output Voltage, VIO +2.7V to +5.5V
    ■ Operating Temp Range -40℃to 105℃
    ■ Package 28-Pin TSSOP
    LMP90100应用:
    ■ Temperature and Pressure Transmitters
    ■ Strain Gauge Interface
    ■ Industrial Process Control

图1.LMP90100方框图

图2.LMP90100典型应用框图

图3.LMP90100应用(1):采用双电流源的3线RTD

图4.LMP90100应用(2):采用单电流源的3线RTD

   图5.LMP90100应用(3):采用CJC热电偶

    LMP90100评估板
     The LMP90100 Evaluation Board Design Kit (consisting of the LMP90100 Evaluation Board, the SPIO-4 Digital Controller Board, the Sensor AFE software, and this user’s guide) is designed to ease evaluation and design-in of National Semiconductor’s LMP90100 24-bit Fully Programmable Low Power ADC with True Continuous Background Calibration.
    Data capturing and static evaluations are simplified by connecting the SPIO-4 Digital Controller Board to a PC via USB and running the Sensor AFE software. The data capture board will generate the SPI signals to communicate to and capture data from the LMP90100. The user will also have the option to evaluate the LMP90100 without using the SPIO-4 board or the Sensor AFE software.
    The LMP90100 will digitize the analog input, and the software will display these results in time domain and histogram.
    The software also allows customers to write to and read from registers, to calibrate the device or the system’s gain, offset, and scale settings, and most importantly, to configure and learn about the LMP90100.
    This document describes the connection between the boards and PC, provide a quick start for a normal DC, 3-wire RTD, and thermocouple/temperature sensor applications, describe how to evaluate the board with and without the SPIO-4 board, and provides the schematic and BOM.
    LMP90100评估板包括:
    1. LMP90100 evaluation board
    2. SPIO-4 digital controller board
    3. Power supplies (optional) to source VA, or VIO, or VREFP.
    4. Multimeter
    5. PC with Sensor AFE software

图6.LMP90100评估板外形图

    图7.LMP90100 DC读数推荐配置图

    图8.LMP90100短路输入和校准测试推荐配置图

图9.LMP90100 PT-100 RTD读数推荐配置图

图10.LMP90100 热电偶和温度传感器电路图

图11.LMP90100热电偶推荐配置图

图12.LMP90100和LM94022推荐配置图

    图13.LMP90100EB评估板电路图

图14.LMP90100EB评估板材料清单（BOM）

    图15.LMP90100EB评估板PCB布局图：顶层

    价格及供货情况

    美国国家半导体LMP90100芯片采用28引脚TSSOP封装，采购以1,000颗为单位，单颗售价为4.95美元，现已批量供货。LMP91000芯片采用14引脚LLP封装，采购以1,000颗为单位，单颗售价为3.95美元，同样已经批量供货。目前美国国家半导体正面向更高速率、更高性能的传感器系统开发多款传感器模拟前端电路，该公司也计划进军医疗设备等产品市场，预计这些新产品将于明年推出。

    美国国家半导体公司简介美国国家半导体是一家位居领导地位的电源管理技术开发商，一直致力为市场提供各种易于使用的模拟集成电路，而且拥有的供应链管理技术及经验，备受业界推崇。该公司的高性能模拟产品可以提高系统的能源效率，因此极受客户欢迎。美国国家半导体的公司总部位于美国加州圣塔克拉拉（Santa Clara），2010 年财年的营业额达 14.2 亿美元。