Maxim公司的MAX12900是超低功耗高度集成的4-20mA传感器发送器,具有10个电路模块:1个宽输入电源LDO,2个支持脉宽调制(PWM)输入的调理器电路,2个低功耗/低失调通用运算放大器,1个宽带/零失调漂移运算放大器,2个诊断比较器,1个带电源就绪输出的上电排序器,可使器件平稳上电,和1个低失调电压基准.主要用在回路供电4-20mA电流发送器,智能传感器,遥控仪器以及工业自动化和过程控制.本文介绍了MAX12900主要优势和特性,功能框图,应用框图以及评估板MAX12900 EVK主要特性,系统框图,电路图,材料清单和PCB设计图.

The MAX12900 is an ultra-low-power, highly integrated 4-20mA sensor transmitter. The MAX12900 integrates ten building blocks in a small package: a wide input supply voltage LDO, two conditioner circuits for pulse-width-modulated (PWM) inputs, two low-power, low-drift, general-purpose operational amplifiers (op amp) one wide bandwidth, zero-offset drift operational amplifier; two diagnostic comparators, a power-up sequencer with power good output to allow for a smooth power-up, and a low-drift voltage reference.

The MAX12900 converts PWM data from a microcontroller into current over a 4-20mA loop with two, three, or four-wire configurations.

The equivalent to an ultra-low-power, high-resolution, digital-to-analog converter is realized with the combination of two-PWM signals received from a microcontroller, the two conditioner circuits, and an active filter built with the integrated low-power op amp. The outputs of the two conditioner circuits provide a stable PWM amplitude over voltage supply and temperature variation. The wide band­width amplifier, in combination with a discrete transistor, converts a voltage input into a current output and allows HART and Foundation Fieldbus H1 signal modulation. The zero-offset operational amplifier and the low-drift voltage reference provide negligible error over wide temperature. The low-power operational amplifier and comparators provide building blocks for enhanced diagnostic features. Supply rail monitoring, output current readback, open circuit and failure detection are a few examples of diagnostic features. All these features, as well as ultra-low-power and high accuracy make the MAX12900 ideal for loop-powered smart sensor transmitters for industrial application.

The MAX12900 is available in 5mm x 5mm 32-pin TQFN package and operates over a wide industrial temperature range of -40℃ to +125℃.

MAX12900主要优势和特性:

Wide Input Supply Range: 4.0V to 36V

Ultra-Low-Power Consumption: 170μA (typ)

High Linearity: 0.01% (Max Error)

High Resolution: Up to 16 Bit

Low Drift Voltage Reference: 10ppm/℃ max

Wide Temperature Range: -40℃ to +125℃

Small Package: 5mm x 5mm x 0.8mm 32-pin TQFN

MAX12900应用:

Loop-Powered 4-20mA Current Transmitter

Smart Sensors

Remote Instrumentation

Industrial Automation and Process Control

图1.MAX12900功能框图

图2.MAX12900两个PWM输入回路供电4-20mA发送器框图

图3.MAX12900带外接电压稳压器回路供电4-20mA发送器框图

图4.MAX12900用于有害环境的回路供电4-20mA发送器框图

评估板MAX12900 EVK

The MAX12900 evaluation kit (EV kit) provides a proven design to evaluate the MAX12900, loop-powered 4–20mA sensor transmitter. The EV kit includes an evaluation board and a graphical user interface (GUI) that provides communication from a PC to the target device through a USB port.

The EV kit includes Windows® 7, Windows 8, and Windows 10 compatible software for exercising the features of the IC. The EV kit GUI allows to set the Coarse and Fine PWM duty cycle inputs to the MAX12900 to control the 4-20mA loop current with ±1μA resolution.

The EV kit must be powered from an external +24V power supply and consumes less than 2.7mA.The MAX12900 EV kit comes with a MAX12900ATJ+ installed in a 32-pin, 5 x 5mm TQFN-EP package.

评估板MAX12900 EVK主要特性:

Loop-powered 4mA–20mA Transmitter with PWM Inputs

Robust Operation with Wide Range Of Input Voltages

On-Board Microcontroller to Generate Two PWM Inputs and Provide Fault Diagnostic

Supports HART and Fieldbus H1 Communication

-40℃ to +125℃ Temperature Range

Reverse Voltage Protection

Proven PCB Layout

Fully Assembled and Tested

Windows 7, Windows 8, and Windows 10 Compatible Software

图5.评估板MAX12900 EVK外形图

图6.评估板MAX12900 EVK系统框图

图7.评估板MAX12900 EVK配置框图

图8.评估板MAX12900 EVK电路图(1)

图9.评估板MAX12900 EVK电路图(2)

评估板MAX12900 EVK材料清单:

图10.评估板MAX12900 EVK PCB设计图(1):左:顶层丝印;右:顶层

图11.评估板MAX12900 EVK PCB设计图(2):内层2

图12.评估板MAX12900 EVK PCB设计图(3):左:内层3;右:底层