±10V analog input and ±15V analog output I/O module for Raspberry Pi

Figure 12. Integral nonlinearity of output voltage

Power architecture

The CN0554 draws power directly from the Raspberry Pi 40-pin interface connector. Figure 13 shows the complete power tree for the CN0554.

Figure 13. CN0554 power tree

The LT8582 is a dual independent channel switching DC/DC converter responsible for boosting and inverting the Raspberry Pi's 5V power supply.

The LT8582 outputs 18V and -18V rails which are then used to provide the necessary power rails for the ADC and DAC. The CN0554 also provides input overvoltage and overtemperature protection through the fault protection features of the LT8582.

The ADM7160 ultralow noise, low dropout regulator provides the 3.3V analog power rail for the AD7124-8. This regulator is powered from the 5V rail on the Raspberry Pi interface connector. The AD7124-8 digital I/O power supply connects directly to the 3.3V rail on the Raspberry Pi.

The LT3090 regulates the -18 V rail to -0.1 V, providing a slightly negative analog supply for the AD7124-8. The rails are designed so that the absolute analog input voltage covers the full range from ground to the reference voltage, even with the input buffers enabled.

Common changes

The AD7124-4 can be used in place of the AD7124-8 with only eight single-ended and/or four differential channels; this reduces cost in applications where the additional channels are not required.

The LTC2686 is an 8-channel replacement for the LTC2688. It features a higher output drive current of 55mA and a compensation pin for driving high capacitive loads.

If only a 0V to 5V output range is required, the LT8582 can be replaced with a single positive 5V supply. Alternative supply options for the DAC could consider lower output current boost or inverting regulators, as the board is designed to support the full DAC output current on all channels.

Additionally, low noise post regulation of a boost or inverting regulator such as a low dropout regulator can be added depending on the application.

Circuit Evaluation and Testing

This section describes the setup and procedures for evaluating the EVAL-CN0554-RPIZ. For complete details, see the CN0554 User Guide.

Equipment requirements

► EVAL-CN0554-RPIZ circuit evaluation board

►Raspberry Pi 4 Model B

►Display with HDMI

► Micro HDMI to HDMI adapter

► USB keyboard and mouse

► 16GB or larger SD card

► Analog Devices Kuiper Linux Image

► 5V, 3A USB Type-C power adapter

►Female to female loopback jumper

► Oscilloscope

►Digital voltmeter (6 digits or higher)

Get started

By default, the ADI CN0554 evaluation board is configured with the correct shunt position for testing. Visit the EVAL-CN0554-RPIZ User Guide to verify the shunt position.

To perform the assessment test, follow these steps:

1. Connect the EVAL-CN0554-RPIZ to the Raspberry Pi as shown in Figure 14.

Figure 14. EVAL-CN0554-RPIZ connected to the Raspberry Pi

2. Insert the SD card with the Kuiper Linux image into the Raspberry Pi.

3. Connect the ADC input and DAC output channels using female-to-female loopback jumper cables as shown in Figure 15.

Figure 15. EVAL-CN0554-RPIZ Test Setup with Loopback Connections

4. Connect the HDMI cable from the Raspberry Pi to the monitor, and connect the keyboard and mouse to the USB ports.

5. Use the USB Type-C power adapter to power the Raspberry Pi and wait for the Raspberry Pi to boot up.

Figure 16. System test setup

6. Open the IIO oscilloscope and undock the DMM and debug tabs as shown in Figure 17.

Figure 17. IIO Oscilloscope DMM and Debug Tabs

7. In the DMM window, select ad7124 as the device and select the channel to be measured, for example ad7124-8: voltage0-voltage1. Click the Play button to start the measurement.

Figure 18. IIO Oscilloscope DMM Window

8. In the debug window, select the ltc2688 in the device selection. In the IIO device properties section, select the output voltage 1 channel and select the raw property. Set the value to 32768 and hit write. This should set the output voltage to around 2.5V, half of the default output range of 0V to 5V.

Figure 19. IIO oscilloscope debug window

9. The DMM measurement should show approximately 0.227V or 1/11 of 2.5V, the default input voltage attenuation.

Figure 20. CN0554 analog I/O loopback measurement

learn more

- ADI CN0554 Design Support Package

- Thoren, Mark and Suteu, Cristina. “A Simple Approach to Analyzing Noise in Mixed-Mode Signal Chains Using Python.” Analog Devices

- Educational video. "Using the Raspberry Pi as a lab instrument with connected simulation." Analog Devices

- Fortunato, Mark. “Successful PCB Grounding with Mixed-Signal ICs—Follow the Path of Least Impedance.” maximintegrated.com

- Meneu, Jean Jacques. “Analog and Digital Grounding: Principles of Mixed-Signal Design.” Arrow.com

- Deprey, Rebecca. “Using Analog Sensors with the Raspberry Pi.” rebeccamdeprey.com

- Introduction to the Raspberry Pi HAT. raspberrypi.com

Data Sheet and Evaluation Board

The data sheets and evaluation boards involved are as follows: LTC2688 Data Sheet, AD7124-8 Data Sheet, AD7124-8 Evaluation Board, LT8582 Data Sheet, LT8582 Evaluation Board, LT3090 Data Sheet, LT3090 Evaluation Board, LT1790 Data Sheet, ADR4525 Data Sheet, LT5400 Data Sheet, ADM7160 Data Sheet, ADM7160 Evaluation Board

ESD Warning

ESD (electrostatic discharge) sensitive devices. Charged devices and circuit boards may discharge without being noticed. Although this product has patented or proprietary protection circuits, the device may be damaged when encountering high-energy ESD. Therefore, appropriate ESD precautions should be taken to avoid device performance degradation or loss of function.

Circuits from the Lab® reference designs are tested reference designs that help accelerate design while simplifying system integration, helping solve today's analog, mixed-signal, and RF design challenges.

LTC2688 16-Channel, 16-Bit Voltage Output SoftSpan™ DAC

AD7124-8 8-Channel, Low Noise, Low Power, 24-Bit, Sigma-Delta ADC with Integrated PGA and Reference

LT8582 Dual 3 A Boost/Inverting/SEPIC DC/DC Converter with Fault Protection

LT3090 -36 V, 600 mA Negative Linear Regulator with Programmable Current Limit

LT1790 Micropower SOT-23 Low Dropout Voltage Reference Series

ADR4525 Ultralow Noise, High Accuracy 2.5 V Voltage Reference

LT5400 Quad Matched Resistor Network

Four-channel matched resistor network

ADM7160 Ultralow Noise, 200 mA Linear Regulator

ADI's Circuits from the Lab™ circuits are designed and built by ADI engineers. Each circuit is designed and built in strict accordance with standard engineering specifications, and the circuit's functionality and performance are tested and verified in a laboratory environment at room temperature. Nevertheless, it is the responsibility of the adopter to test the circuit and determine whether it is suitable for use. Therefore, ADI will not be responsible for direct, indirect, special, incidental, consequential or punitive damages caused by any cause or any item connected to any reference circuit used.

Circuits from the Lab circuits are intended for use with ADI products only and the intellectual property rights are owned by ADI or its licensors. Although you may use the reference circuits in your product designs, no other licenses are granted by implication, and no patents or other intellectual property rights are acquired through the application or use of the reference circuits. ADI believes that the information provided is accurate and reliable. However, Circuits from the Lab circuits are provided "as is" without warranty of any kind, including, but not limited to, express, implied or statutory warranties of merchantability, non-infringement or fitness for a particular purpose, and ADI does not assume any responsibility for the use of the reference circuits, nor for any infringement of any patent or other third party rights that may be caused by their use. ADI reserves the right to modify any reference circuit at any time without notice.

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