基于LMP8358的高精度可编增益仪表放大器设计方案

NS 公司的LMP8358是高精度可编增益仪表放大器，通过SPI兼容的串口或并口可把增益编程为0,20,50,100,200,500,或1000，也可用两个外设电阻设定为任意值．单电源2.7V 到5.5V工作，电流为1.8 mA，增益最大误差为0.15%，增益漂移为16 ppm/℃，CMRR大于110 dB，失调电压小于10 μV，失调电压漂移小于50 nV/℃，增益带宽GBW(增益=10)8MHz，非线性小于100 ppm，主要用在桥接传感器放大，热堆放大，手提仪表，医疗设备．本文主要介绍LMP8358主要特性，功能方框图，典型应用方框图，菊花和星形链接配置图以及差分桥接传感器应用电路图．

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应用：

■ Bridge sensor amplifier

■ Thermopile amplifier

■ Portable instrumentation

■ Medical instrumentation

■ Precision low-side current sensing

图１．LMP8358方框图

图２．LMP8358典型应用方框图

图３．LMP8358菊花链接配置图

图４．LMP8358每个寄存器不同写入值的星形链接配置图


图５．LMP8358差分桥接传感器应用电路图