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TI公司的LMP91000是可編程低功耗化學傳感器模擬前端(AFE),提供傳感器和MCU間完整的信號通路解決方案.氣體靈敏度從0.5 nA/ppm到9500 nA/ppm,很容易轉換成電流從5μA 到750μA.工作電壓2.7V-5.25V工作電流小于10 μA,電池調理電流高達10mA,可編程電池偏壓電壓, 偏壓電壓漂移低.主要用在化學樣品識別,電流計和電化學血糖儀.本文介紹了LMP91000主要特性,方框圖,多種應用框圖以及化學和氣體傳感器解決方案框圖和藹主要特性. LMP91000 Sensor AFE System: Configurable AFE Potentiostat for Low-Power Chemical Sensing Applications The LMP91000 is a programmable Analog Front End (AFE) for use in micro-power electrochemical sensing applications. It provides a complete signal path solution between a sensor and a microcontroller that generates an output voltage proportional to the cell current. The LMP91000’s programmability enables it to support multiple electrochemical sensors such as 3-lead toxic gas sensors and 2-lead galvanic cell sensors with a single design as opposed to the multiple discrete solutions. The LMP91000 supports gas sensitivities over a range of 0.5 nA/ppm to 9500 nA/ppm. It also allows for an easy conversion of current ranges from 5μA to 750μA full scale. The LMP91000’s adjustable cell bias and transimpedance amplifier (TIA) gain are programmable through the the I2C interface. The I2C interface can also be used for sensor diagnostics. An integrated temperature sensor can be read by the user through the VOUT pin and used to provide additional signal correction in the μC or monitored to verify temperature conditions at the sensor. The LMP91000 is optimized for micro-power applications and operates over a voltage range of 2.7V to 5.25V. The total current consumption can be less than 10μA. Further power savings are possible by switching off the TIA amplifier and shorting the reference electrode to the working electrode with an internal switch. LMP91000主要特性: Typical Values, TA = 25℃ ■ Supply voltage 2.7 V to 5.25 V ■ Supply current (average over time) <10 μA ■ Cell conditioning current up to 10 mA ■ Reference electrode bias current (85℃) 900pA (max) ■ Output drive current 750μA ■ Complete potentiostat circuit to interface to most chemical cells ■ Programmable cell bias voltage ■ Low bias voltage drift ■ Programmable TIA gain 2.75kΩ to 350kΩ ■ Sink and source capability ■ I2C compatible digital interface ■ Ambient operating temperature -40℃ to 85℃ ■ Package 14 pin LLP ■ Supported by Webench Sensor AFE Designer LMP91000應用: ■ Chemical species identification ■ Amperometric application ■ Electrochemical blood glucose meter 
圖1. LMP91000方框圖
圖2. LMP91000 AFE氣體檢測器框圖
圖3. LMP91000 3線電流計單元框圖
圖4. LMP91000 2線原電池接地框圖
圖5. LMP91000 2線原電池在恒電勢器配置圖
圖6. LMP91000在I2C總線的智能氣體傳感器模擬前端(AFE)連接圖 Electrochemical sensors are widely used as a sense mechanism for gas and chemical sensing. Common applications include carbon monoxide detectors, chemical species identification, Amperometric sensors etc. Electrochemical sensors can be considered simply as transducers that convert the physical characteristic of gas/chemical concentration to an electrical signal which can be processed by instrumentation. Signal Conditioning: The programmable Analog Front End (AFE) is perfect for use in micro-power electrochemical sensing applications. It provides a complete signal path solution between a sensor and a microcontroller that generates an output voltage proportional to the cell current. The programmability enables it to support multiple electrochemical sensors such as 3-lead toxic gas sensors and 2-lead galvanic cell sensors with a single design as opposed to the multiple discrete solutions. The AFE supports gas sensitivities over a range of 0.5 nA/ppm to 9500 nA/ppm. It also allows for an easy conversion of current ranges from 5µA to 750µA full scale. The adjustable cell bias and Transimpedance amplifier (TIA) gain are programmable through the I2C interface. The I2C interface can also be used for sensor diagnostics. An integrated temperature sensor can be read by the user through the VOUT pin and used to provide additional signal correction in the µC or monitored to verify temperature conditions at the sensor. The AFE is optimized for micro-power applications and operates over a voltage range of 2.7V to 5.25V. The total current consumption can be less than 10μA. Further power savings are possible by switching off the TIA amplifier and shorting the reference electrode to the working electrode with an internal switch. Signal Acquisition and Processing: TI’s high resolution differential ADCs have low power consumption, wide dynamic range and low noise. This can be used to digitize the conditioned analog bridge output for high resolution, precision measurements. Alternately, one could use TI’s MSP430 microcontrollers with integrated ADCs and DACs. Further post processing algorithms can be run on this MCU. Interface and Communication: Traditional analog (4 - 20mA) interface remains the popular choice for industrial control and sensor applications. The other popular protocols include HART, Profibus and IO-Link. TI’s IO-Link interface products have integrated regulators and diagnostic outputs. In addition, wireless options based on IEEE 802.15.4 protocols are becoming more prevalent. TI is committed to provide solutions for both traditional and emerging industrial interfaces. Power Management The Field Transmitter can be powered in one of three ways. Line powered transmitters are commonly powered by voltage rails of 12V, or 24V. Loop powered transmitters are powered by the 4-20 mA loop. Such transmitters require extremely low power architectures as the entire solutions has to be powered off the loop. TI provides high efficiency Step Down converters with low quiescent current and low output ripple appropriate for Line and Loop powered transmitters. Battery powered transmitters powered can be designed using TI’s low power Buck and Buck-Boost converters. The DC/DC buck converters offer over 95% efficiency over a wide battery voltage range, even with input voltage down to 1.8 volts extending battery life. Special Buck-Boost converters generate a stable required output voltage and supply constant current for over- and under-input voltage conditions and support various battery configurations.
圖7. LMP91000化學和氣體傳感器解決方案框圖 解決方案主要特性: Configurable AFE with integrated electrode excitation One design solution fits multiple electro-chemical sensors 16-bit MCU for configuration and communication Extremely low power extends battery life and ensures operation under 4mA Enables online or factory programmed configuration and calibration of sensor 4-20mA Current Loop Transmitter Integrated 5V regulator capable of providing system power .05% span error 詳情請見: 
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