免费注册
应用与设计

Maxim 设计资源 参考设计 系统板 评估板 参考电路 Important Notice for Maxim Integrated Design Information and Resources

MAXREFDES77#：双通道电流检测外设模块

Maxim Integrated

MAXREFDES77#外设模块提供了必要的硬件电路，使得MAX44285双通道高边检流放大器可连接至任何使用兼容Pmod™扩展端口配置SPI通信的系统。IC具有一路共模输入，电压范围为2.7V至76V，80kHz小信号带宽，理想用于连接SAR ADC，用于多通道、多路复用数据采集系统。

关于IC的详细操作信息，请参考MAX44285 IC数据资料；关于Munich电路板及GUI的详细信息，请参考USB2PMB1# (Munich)适配器电路板数据资料。

特性

  • 2.7V至76V输入共模电压
  • 12μV (最大)低输入失调电压
  • 0.1% (最大)低增益误差
  • 增益 = 20V/V和100V/V
  • 符合RoHS标准
  • 经过验证的PCB布局
  • 完全安装并经过测试
MAXREFDES77#系统板 放大+
详情介绍

SPI Interface

The MAXREFDES77# peripheral module can plug directly into a Pmod-compatible port (configured for SPI) through connector X1. For information on the SPI protocol, refer to the MAX11125 IC data sheet.

Connector X1 provides connection of the module to the Pmod host. See Table 1 for detailed description.

Connectors X3 and X4 provide connection to external power and the system loads.

Voltage Reference

The MAXREFDES77# peripheral module contains the MAX6126A30+ voltage reference to provide 3.0V reference to the ADC MAX11125.

Temperature Sensor

The MAXREFDES77# peripheral module also contains a temperature sensor, MAX6607IXK+, to measure the external temperature.

Software (GUI)

The Munich GUI is available for download and is provided to facilitate the evaluation of the MAXREFDES77#. Refer to the Munich GUI Quick Start Guide document for further details.


MAXREFDES77# System Board 放大+

Table 1. Connector X1 (SPI Communication)

Pin Signal Description
1 SPI_CS Chip Select. Assert low to enable the SPI interface.
2 N.C. No Connection
3 SPI_MOSI MAX44285 Serial Data Input
4 Active-Low CONVST ADC Conversion Control Input. Assert low to initiate an ADC conversion.
5 SPI_MISO MAX44285 Serial Data Output
6 Active-Low EOC End of Conversion Output. Data is valid after active-low EOC pulls low.
7 SPI_SCLK MAX44285 Serial Clock Input
8 N.C. No Connection
9 GND Ground
10 GND Ground
11, 12 +3.3V +3.3V Power Supply

Step-by-Step Guide

The MAXREFDES77# allows measuring supply-voltage (up to 65V) and supply-current (up to 26A) for 2 different loads with independent supplies.

Procedure

  1. Connect supply voltage between RS+ and GND.
  2. Connect load resistor between RS- and GND.
  3. Connect the MAXREFDES77# to the Munich via the Pmod connector.
  4. Connect the Munich board to a PC via a USB cable as shown in Figure 1.
  5. In the Munich GUI, select REFDES77 – Current Sense under the Device tab.
  6. Click Scan Adapter.
  7. Press Connect. Munich GUI will then allow you to start sampling from the MAXREFDES77# board.
  8. Click Sample continuously. The Munich GUI will then plot the selected Physical Values and update static levels in real time. The Y-axis on the left shows the voltage. The second Y-axis on the right depicts the Current, and the third Y-axis on the far right displays the temperature. Scaling the Y-axes can be done manually in the calibration window, so the range of interest can be plotted.
  9. Press the Calibrate button to perform linear calibration for accurate measurements. When in calibration mode, it is necessary to select ADC Counts in the Plot Configuration and keep Sample continuously running. See Figure 2.

    Figure 1. MAXREFDES77# connected to Munich board.

    Figure 2. MAXREFDES77#/Munich GUI.

    • Offset calibration
      To perform offset calibration, connect both RS1- and RS2- to GND. Then observe and enter the numbers printed in Physical Values box to the appropriate Offset Textboxes (voltage and current).
    • Volt per LSB calibration
      To perform Volt per LSB calibration, apply a known voltage to both RS1- and RS2-. Note that the measurement range is up to 65V, but for good calibration the applied voltage should be < 75% of the allowed range. Use an accurate multimeter that has 1mV or better accuracy. See Figure 3. Divide the applied voltage level (i.e. 60V) by the number shown in Physical Value box. Then subtract the 0V Offset. The result yields the weight of 1 LSB, which should be about 0.0165V.

      • Volt per LSB = 60V/(ADCcounts at 60V - ADCcounts at 0V)

    • Ampere per LSB calibration
      To perform ampere per LSB calibration, apply a known voltage to RS+ and connect a load from RS- to GND. Then, measure the current through the load with an ampmeter. There are two available gain options: 20x (MAX44285T) and 100x (MAX44285H). If the gain is 20, then the current-range is up to ~27A. If the gain is 100, then the current range is up to ~5.4A.

      • For accurate calibration, use load with current at ~75% of the range.

      A per LSB = 20A/(ADCcounts at 20A - ADCcounts at 0A)

      The Munich GUI automatically saves these calibration settings once the calibration menu is closed. Therefore, if the same hardware is used, it is not neccesarry to re-calibrate.

      Calibration menu. Figure 3. Calibration menu.

Lab Measurements

The MAXREFDES77# reference design was verified and tested under full input range and different output load conditions, and the results were captured by Munich GUI as shown in Figure 4.

Figure 4. MAXREFDES77# lab measurements.

Pmod is a trademark of Digilent Inc.