基于LMP8358的高精度可編增益儀表放大器設計方案

NS 公司的LMP8358是高精度可編增益儀表放大器，通過SPI兼容的串口或并口可把增益編程為0,20,50,100,200,500,或1000，也可用兩個外設電阻設定為任意值．單電源2.7V 到5.5V工作，電流為1.8 mA，增益最大誤差為0.15%，增益漂移為16 ppm/℃，CMRR大于110 dB，失調電壓小于10 μV，失調電壓漂移小于50 nV/℃，增益帶寬GBW(增益=10)8MHz，非線性小于100 ppm，主要用在橋接傳感器放大，熱堆放大，手提儀表，醫療設備．本文主要介紹LMP8358主要特性，功能方框圖，典型應用方框圖，菊花和星形鏈接配置圖以及差分橋接傳感器應用電路圖．

The LMP8358 is a precision programmable-gain instrumentation amplifier in National’s LMP precision amplifier family. Its gain can be programmed to 10, 20, 50, 100, 200, 500, or 1000 through an SPI-compatible serial interface or through a parallel interface. Alternatively, its gain can be set to an arbitrary value using two external resistors. The LMP8358 uses patented techniques to measure and continuously correct its input offset voltage, eliminating offset drift over time and temperature and the effect of 1/f noise. Its ground-sensing CMOS input features a high CMRR and low input bias currents. It is capable of sensing differential input voltages in a commonmode range that extends from 100mV below the negative supply to 1.4V below the positive supply, making it an ideal solution for interfacing with ground-referenced sensors, supply- referenced sensor bridges, and any other application requiring precision and long-term stability. Additionally, the LMP8358 includes fault detection circuitry to detect open and shorted inputs and deteriorating connections to the signal source. Other features that make the LMP8358 a versatile solution for many applications are its rail-to-rail output, low input voltage noise and high gain-bandwidth product.

LMP8358主要特性：

Typical Values unless otherwise noted, TA = 25℃

■ Supply voltage 2.7V to 5.5V

■ Supply current 1.8 mA

■ Max gain error 0.15%

■ Max gain drift 16 ppm/℃

■ Min CMRR 110 dB

■ Max offset voltage 10 μV

■ Max offset voltage drift 50 nV/℃

■ GBW (gain = 10) 8 MHz

■ Max non-linearity 100 ppm

■ Operating temperature range ?40℃ to 125℃

■ Input fault detection

■ SPI or pin configurable modes

■ EMIRR at 1.8GHz 92 dB

■ 14-Pin SOIC and 14-Pin TSSOP Package

LMP8358應用：

■ Bridge sensor amplifier

■ Thermopile amplifier

■ Portable instrumentation

■ Medical instrumentation

■ Precision low-side current sensing

圖１．LMP8358方框圖

圖２．LMP8358典型應用方框圖

圖３．LMP8358菊花鏈接配置圖

圖４．LMP8358每個寄存器不同寫入值的星形鏈接配置圖


圖５．LMP8358差分橋接傳感器應用電路圖