MAXREFDES60#具有16位、高精度、0V–10V模拟输出，电源和数据隔离。MAXREFDES60#设计集成低噪声、快速稳定缓冲器(MAX9632)；16位、低功耗DAC (MAX5216)；超高精度4.096V电压基准(MAX6126)；600VRMS数据隔离(MAX14850)；STMicroelectronics® STM32F4微控制器；FTDI USB-UART桥；高效DC-DC转换器(MAX17552)；隔离/稳压+15V、+5.5V和-3V电源(MAX17498C/MAX8719/MAX1659/MAX1735)。整个系统的功耗通常小于250mW，适合用于信用卡大小的空间。用于工业微型PLC领域时，MAXREFDES60#可用于任何要求高精度模拟输出的应用。
Industry 4.01 marks the fourth industrial revolution, characterized by distributed, intelligent control systems. Breaking from a past with large, centralized programmable-logic controllers, Industry 4.0 allows for highly configurable, highly modular factories to provide analog signal controls to numerous equipment and operate at a higher output than ever before. The ultra-small PLC, or Micro PLC, lies at the heart of the Industry 4.0 factory, providing high performance with ultra-low power consumption in an ultra-small package. The MAXREFDES60# is Maxim’s Micro PLC analog output card.
The MAXREFDES60# features a 16-bit, high-accuracy 0V–10V analog output with isolated power and data. The MAXREFDES60# design integrates a low-noise, fast-settling buffer (MAX9632); a 16-bit, low-power DAC (MAX5216); an ultra-high precision 4.096V voltage reference (MAX6126); 600VRMS data isolation (MAX14850); a STMicroelectronics® STM32F4 microcontroller; an FTDI USB-UART bridge; a high-efficiency DC-DC converter (MAX17552); and isolated/regulated +15V, +5.5V, and -3V power rails (MAX17498C/MAX8719/MAX1659/MAX1735). The entire system typically operates at less than 250mW and fits into a space roughly the size of a credit card. While targeted for industrial Micro PLC applications, the MAXREFDES60# can be used in any application that requires high-accuracy analog output.
Figure 1. The MAXREFDES60# reference design block diagram.
The power requirement is shown in Table 1.
Table 1. Power Requirement for the MAXREFDES60# Reference Design
|Power Type||Input Voltage (V)||Input Current (mA, typ)|
|On-board isolated power||24||10|
Note: STM32 and FTDI are powered by USB separately.
The analog output circuit consists of a 16-bit, rail-to-rail DAC MAX5216 (U401) and a low-noise fast-settling operational amplifier MAX9632 (U403). The DAC’s reference input is driven by an ultra-high precision 5V voltage reference, the MAX6126 (U402), with 0.02% initial accuracy and a 3ppm/°C maximum temperature coefficient (tempco). The output of the DAC is 0V to 5V, and the op amp amplifies the signal to 0V to 10V plus 20% margin.
The MAXREFDES60# uses the ultra-efficient MAX17498C (U501) to generate the isolated +17.5V, +7.5V, and -5V rails from a 24V supply. The MAX8719 (U102), MAX1659 (U103), and MAX1735 (U104) provide post-regulated +15V, +5.5V, and -3V rails. The MAX14850 (U301) digital data isolators provide data isolation. The combined power and data isolation achieved is 600VRMS.
The MAX17552 (U101) step-down DC-DC converter converts the +5V supply from the USB to +3.3V and powers the STM32 (U1) microcontroller and FTDI (U201) USB-UART bridge.
The equation to convert the DAC code to output voltage is:
VOUT = 12 × CODEDAC/65536
The MAXREFDES60# uses the on-board STM32F4 microcontroller to communicate with the DAC.The user sets the DAC output code through a terminal program.The user can also use the MAXREFDES60# to generate a customized sine wave. The simple process flow is shown in Figure 2. The firmware is written in C using the Keil® µVision® 5 tool.
Figure 2. The MAXREFDES60# firmware flowchart.
The firmware accepts commands, writes statuses, and is capable of generating a user-customized sine wave. The complete source code is provided to speed up customer development. Code documentation can be found in the corresponding firmware platform files.
The reference design is fully assembled and tested. Follow the steps below to verify board operation:
Figure 3. Terminal program main menu.
Measurements of DNL, INL, and TUE for the 0V to 10V voltage output with a 20% overrange are shown in Figure 4, Figure 5, and Figure 6, respectively.
Figure 4. DNL for 0V to 10V output with 20% overrange.
Figure 5. INL for 0V to 10V output with 20% overrange.
Figure 6. Output error for 0V to 10V output with 20% overrange.
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