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EVAL-CN0508-RPIZ Overview

CN0508 provides a single-channel, 75-watt bench power supply featuring an adjustable output voltage of 0V to 27.5V, and constant current limiting of 0A to 3A using the combination of parallel LT3081 linear regulators, a synchronous step-down LT8612, a LT3092 current source, and a tiny LTC1983 negative supply.

The output voltage can be set manually using a potentiometer or digitally via Raspberry Pi with a AD5683R digital to analog converter (DAC), through the “analog- AND” function circuit. Moreover, a AD7124-4 24-bit, sigma-delta analog to digital Converter (ADC) provides measurement reading of output voltage and output current as well as other diagnostic parameters.

The circuit features low output ripple with low output capacitance, excellent transient response, remains in regulation during short-circuit and stays cool with no bulky heat sinks. It can easily be coupled with an AC/DC converter or it can be powered from a DC source.

Figure 1. EVAL-CN0508-RPIZ Circuit Evaluation Board

Features

Provides a single, 0-27.5V DC adjustable output with manual and software control via Raspberry Pi
Provides 0-3A constant current limit
Supports both HDMI displays and local touchscreens (TFT screens)
Features low output ripple with low output capacitance
Excellent transient response
Stays cool with no bulky heat sinks

Videos

Documents Needed

CN0508 Circuit Note

Equipment Required

Hardware
- EVAL-CN0508-RPIZ Circuit Evaluation Board
- Raspberry Pi Zero W
- 75W to 120W offline power supply or b
- Bench power supply (Globtek TR9CR3000T00-IM(R6B))
- Various power resistors, dummy load, or test circuits with known power consumption
- 40-pin ribbon cable (optional)
- Monitor with HDMI display
- Mini HDMI to HDMI adapter
- HDMI to HDMI cable
- 16GB or larger SD card
- Micro-USB dongle
- USB keyboard and mouse
- USB hub
Software
- ADI Kuiper Linux image

Block Assignments

Figure 2. EVAL-CN0508-RPIZ Circuit Evaluation Board Top View
Figure 3. EVAL-CN0508-RPIZ Circuit Evaluation Board Side View

Connector P1 is the screw terminal block for the input supply
Connector P2 is the 5.5mm x 2.5mm barrel jack connector for input supply
Connector P3 is the 40-pin connector for Raspberry Pi
Connector P7 is the positive output jack of the bench supply
Connector P8 is the ground output jack of the bench supply
Potentiometer R43 is the manual control of output voltage
Potentiometer R14 is the manual control of the output current limit
Header P12 contains the output signal for the fan control

Running the System

Figure 4. Test Setup Functional Block Diagram

Set solder jumpers for the desired settings.
Proceed with the hardware setup. Ensure the input supply, Raspberry Pi, load, and fan are all properly connected.
Burn the SD card with the latest ADI Kuiper Linux image. Insert the flashed SD card into designated slot on Raspberry Pi.
Turn on the input supply. Wait for the Raspberry Pi to boot up.
Open the terminal and configure the device tree overlay file. See software section for detailed instructions. Make sure to reboot the Raspberry Pi after saving the config.txt file.
Wait for the Raspberry Pi to boot up again. Open the IIO Oscilloscope and select the CN0508 tab.
You may change output voltage and view the measurements on other parameters such as current, temperature, and potentiometer knob readings.
For manual control, rotate the knob of R43. The output voltage of the system follows the lower voltage between the output voltages of the potentiometer and the DAC.
You may also change the current limit of the system by turning the knob of R14.
The Raspberry Pi must be powered down properly in order to prevent eventual corruption of the SD card. This can be done by pressing S1 and waiting for the green heartbeat LED to stop blinking. At that point, power is safe to be removed.
Alternatively, click the ADI logo, scroll to the bottom, click power off, and wait for the heartbeat LED to stop blinking. Power is safe to be removed.

Solder Jumper Settings and Configuration

The CN0508 has six jumper headers which configure different settings as shown below. Also, the default shunt positions are highlighted.
Figure 5. EVAL-CN0508-RPIZ Evaluation Board Solder Jumper Guide

-VCC: Negative Vcc Supply

VCC selects the negative supply of the LT6015 amplifiers. By default, the shunt is placed connecting pin 1 and 2 to source supply from -5V output of LTC1983.

-Vcc Shunt Position	Negative Supply of LT6015
1 and 2	-5V
2 and 3	Ground

Connecting Pins 1 and 2 connects the LT6015 V- to -5V, allowing operation at ground
Connecting Pins 2 and 3 connects the LT6015 V- ground

CS_ADC: ADC Chip Select Mapping

CS_ADC selects the mapping of the AD7124-4 ADC chip select to RPi. By default, the shunt connects pin 1 and 2 which selects GPIO27.

CS_ADC Position	CS_ADC Mapping to RPi
1 and 2	GPIO27 (Pin 13)
2 and 3	CS0 (Pin 24)

Connecting Pins 1 and 2 maps the ADC chip select to GPIO27
Connecting Pins 2 and 3 maps the ADC chip select to CS0

CS_DAC: DAC Chip Select Mapping

CS_DAC selects the mapping of the AD5683R DAC chip select to RPi. By default, the shunt connects pin 1 and 2 which selects GPIO22.

CS_DAC Position	CS_DAC Mapping to RPi
1 and 2	GPIO22 (Pin 15)
2 and 3	CS1 (Pin 26)

Connecting Pins 1 and 2 maps the DAC chip select to GPIO22
Connecting Pins 2 and 3 maps the DAC chip select to CS1

ADC_INT: ADC Interrupt Mapping

ADC_INT selects the mapping of the AD7124-4 interrupt from its DOUT/RDY pin to RPi. By default, the shunt connects pin 1 and 2 which selects GPIO23.

ADC_INT Position	ADC_INT Mapping to RPi
1 and 2	GPIO23 (Pin 16)
2 and 3	GPIO25 (Pin 22)

Connecting Pins 1 and 2 maps the ADC interrupt to GPIO23
Connecting Pins 2 and 3 maps the ADC interrupt to GPIO25

VCTRL: Output Voltage Control

VCTRL enables users to choose how to control the output voltage between electronic and manual mode (chooses the lower setting between the two) versus exclusively manual mode. Output can be controlled electronically through the DAC and manually through the potentiometer knob. By default, the shunt connects pin 1 and 2 which enables both electronic and manual control.

VCTRL Position	VCTRL Mapping
1 and 2	Electronic and Knob control
2 and 3	Knob control

Connecting Pins 1 and 2 selects both electronic and knob control mode
Connecting Pins 2 and 3 selects purely knob control mode

EEPROM_ID: EEPROM Address Selection

EEPROM_ID sets the EEPROM I2C address. It consists of P4, P5, and P6 solder jumpers connected respectively to A2, A1, and A0 address selection pins of U7. The default address configuration is “111”. This EEPROM I2C address is configurable from 001 to 111. It cannot be set to “000” since U4 already uses this address for RPi HAT identification.

A0	A1	A2	Address Set
0	0	1	0x51
0	1	0	0x52
0	1	1	0x53
1	0	0	0x54
1	0	1	0x55
1	1	0	0x56
1	1	1	0x57

Hardware Setup

Setting up and Connecting the Raspberry Pi

The output display of the system will be through an external monitor with HDMI capability. To do this, connect the mini HDMI to HDMI adapter on the Raspberry Pi Zero W mini HDMI slot. Connect the external monitor through this port. Figure 6. Hardware connection of Raspberry Pi to Monitor Display
Connect a micro-USB to USB Type A female adapter on the USB port of the Raspberry Pi Zero W. This shall allow us to connect a mouse/keyboard or even a USB hub to be able to connect both for controlling the Raspberry Pi upon boot up. Figure 7. Hardware connection of Input Devices to Raspberry Pi
Raspberry Pi connects to the EVAL-CN0508-RPIZ through P3 which is a 40-pin connector. You may do this directly by connecting the RPi on the bottom side of the connector or through a 40-pin ribbon cable. Hardware connection of CN0508 Board and Raspberry Pi Figure 8. Hardware connection of EVAL-CN0508-RPIZ and Raspberry Pi Zero W

Input Supply

Power to the EVAL-CN0508-RPIZ can be connected through P1 or P2. P1 is a two-terminal screw terminal while P2 is a 5.5mm x 2.5mm center positive barrel jack. Please choose only one input between the two. The maximum input rating to the circuit is at 40V 3A or 120W. Figure 9. Hardware Connection of Input Power Supply to EVAL-CN0508-RPIZ

Output connections

You can connect a resistive load/test circuit, an electronic load, or multimeter at the output banana jacks P7 and P8. P7 is the positive polarity and P8 is the ground. Also, make sure you are aware of your load's power consumption to avoid overheating. Figure 10. EVAL-CN0508-RPIZ Evaluation Board Output Connections

Figure 11. EVAL-CN0508-RPIZ Evaluation Board Connected to a Load

Connecting a fan

Cooling requirements for EVAL-CN0508-RPIZ are low but it still contains a control circuit for a fan. If either of the regulators' temperature readings hit 60 Celsius and above, the 5V power for the fan on P12 turns on. Figure 12. Hardware Connection of EVAL-CN0508-RPIZ to a Fan

Software Setup

Loading CN0508 Image on SD Card

In order to control the CN0508 from the Raspberry Pi, you will need to install ADI Kuiper Linux on an SD card. Complete instructions, including where to download the SD card image, how to write it to the SD card, and how to configure the system are provided at Kuiper Images.
Write the image and follow the system configuration procedure.

Configuring the SD Card

Follow the Hardware Configuration procedure under Preparing the Image: Raspberry Pi in the [:resources:tools-software:linux-software:kuiper-linux |Kuiper Images]] page, substituting the following lines in config.txt:

dtoverlay=rpi-cn0508,rotate=270,speed=64000000,fps=30
hdmi_cvt=720 480 60 1 0 0 0
dtparam=spi=on
dtparam=i2c1=on
dtparam=i2c_arm=on
dtoverlay=gpio-shutdown,gpio_pin=17,active_low=1,gpiopull=up
dtparam=act_led_gpio=13
dtparam=act_led_trigger=heartbeat

The lines below the “dtoverlay” enable additional hardware features, including a heartbeat LED (DS3, green) and a shutdown button (S1) that allows the Raspberry Pi to be shut down properly before disconnecting power.

Make sure to have the latest version of IIO Oscilloscope. Complete instructions and update scripts are found at Analog Devices IIO Oscilloscope.

Electronic Control and Diagnostics via IIO Oscilloscope Plugin

EVAL-CN0508-RPIZ allows electronic control of the output voltage and measurement display of other system diagnostics such as voltage, current, and temperature through the AD7124-4 ADC. All of these are incorporated and displayed in the designated plugin for CN0508 in IIO Oscilloscope.
Figure 13. Graphical User Interface (GUI) window of ADI IIO Oscilloscope

DAC output

Setting this value from 0 to 65535 will vary the output voltage of the DAC.

Temperature Monitor

This shows the temperature readings of the two LT3081. While power dissipation is kept low in the LT3081 devices, operating at high currents with restricted airflow can result in an over-temperature condition.

DC Supply

This presents the output voltage and output current of the EVAL-CN0508-RPIZ. The output voltage is set to the lower of the output voltages between the DAC and potentiometer.

Potentiometers

This shows the position of the voltage and current limit potentiometers. An indicator flag is raised if the output current reaches 95% of the current limit setpoint or if the measured output voltage falls more than 0.5V below the lower of (DAC setpoint, potentiometer setpoint).

Input Supply

This displays the input voltage on P1 or P2 connectors.

Schematic, PCB Layout, Bill of Materials, Casing

EVAL-CN0508-RPIZ Front Panel Casing File

Front Panel Casing in .svg file

EVAL-CN0508-RPIZ Design & Integration Files

Schematics
PCB Layout
Bill of Materials
Allegro Project
LTSpice Simulations

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