RoadTest: Enroll to Review the Analog Devices Digital Isolator Eval Kit - MAX2256XAEVKIT#
Author: taifur
Creation date:
Evaluation Type: Evaluation Boards
Did you receive all parts the manufacturer stated would be included in the package?: True
What other parts do you consider comparable to this product?: ISO77XX and ISO67XX Series from Texas Instruments, 2DIB0400, 2DIB0410 from Infineon, IL600 Series from NVE Corporation, and Si86xx from Silicon Lab.
What were the biggest problems encountered?: Soldering was a bit tricky.
Detailed Review:
Galvanic isolation is a necessary form of protection for all electronics that interface with humans or other circuits in the presence of possible high-voltage events from strong electromagnetic fields, surge voltages, transient voltages, and high EMC noise. In the case of human safety or even electronic protection, a high-voltage event can range from tens of volts to kilovolts. Over the past several decades, the technology used to isolate circuits has moved from optical-based optocouplers to silicon-based digital isolators for lower power consumption and improved performance. Digital isolation focuses on the transmission of digital signals across an isolation barrier. Digital isolators transfer signals without establishing a direct electrical connection between the input and output.
A number of technologies have been developed in the field of digital isolation to provide efficient isolation. These technologies, which are basically magnetic coupling, optical coupling, and capacitive coupling, each have unique properties and working principles.
A typical digital isolator consists of two isolated supplies-- VCC1 and VCC2-- two grounds-- GND1 and GND2-- and input and output pins on either side referred to the respective grounds. The input signal is modulated through a transmit circuit and then passed through a high voltage capacitive barrier and across the connecting bond wire to the receiving side circuit.
Logic levels for the digital isolators can range from 1.8 to 5.5 volts for both supplies, VCC1 and VCC2, though some devices may support a larger supply range.
Digital isolators are most commonly used with isolated power supplies on separate grounds, which is also useful in preventing ground interference and noise currents from power supplies. Digital isolators also help when potential ground differences are present. In addition, digital isolators are used to eliminate any errors due to ground loops. In some cases, digital isolation ensures accuracy too.
The digital isolator should have a low latency or propagation delay, low noise, and a high data rate.
The MAX22565 is a 6-channel reinforced, fast, low-power digital galvanic isolator from Analog Devices. This device transfers digital signals between circuits with different power domains, using as little as 0.71mW per channel at 1Mbps (1.8V supply). The low-power feature reduces system dissipation, increases reliability, and enables compact designs. The device is available with a maximum data rate of either 25Mbps or 200Mbps and with user-selectable default-high or default-low outputs. It features 7ns low propagation delay and low clock jitter, which reduces system latency. Independent 1.71V to 5.5V supplies on each side also make the device suitable for use as level translators. The MAX22565 provides five channels transmitting signals in one direction and one in the opposite.
The MAX2256XA is an evaluation kit that has the flexibility to install the desired version of the MAX22563−MAX22566 family of reinforced, six-channel, unidirectional digital isolators. On the other side, MAX2256CA comes with a preinstalled MAX22565 isolator. This board can be a nice choice for testing and experimenting with MAX22563−MAX22566 six-channel digital isolators. The board has 6 SMA connectors for 6 input channels and 6 SMA connectors for 6 output channels. Without SMA connectors the board also offers standard male pin headers for all channels. So, if you don’t have SMA connectors to connect with the board SMA you can still access any channel using pin header.
The board came inside a rectangular-shaped cardboard box and inside the box, it was wrapped with pink elastic packaging foam.
Inside the wrapping, the board was placed in an ESD safe bag. After opening the cardboard box, then the packaging foam, and then the ESD safe bag, the MAX2256CAEVKIT finally came out.
The color and look were really gorgeous.
When I was taking the image of the board my iPhone camera automatically detected the QR code and read the link from the code.
I am pleased with the design of the board. The board has four 2 positioned jumpers named ENA, ENB, DEFA, and DEFB. ENA and ENB jumpers are for enabling and disabling the input and output side. DEFA and DEFB are for setting the default output to high or low in side A and side B respectively. The board has two VDD and two GND inputs for connecting two separate power supplies on two sides. Both sides can tolerate from 1.71V to 5.5V. Each power supply is decoupled with a 1μF ceramic capacitor in parallel with a 0.1μF ceramic capacitor, which are placed close to the U1 VDDA and VDDB pins. It is possible to provide the same voltage on both sides but in the real scenario, digital isolators operate from separate sources in most of the cases. On the MAX22565CA EV kit, SMA connectors A1−A5 and B6 are inputs, and SMA connectors B1−B5 and A6 are outputs.
The following screenshot was taken from the datasheet that shows a test setup of the board.
In the board, the input and output traces of all six isolation channels have an impedance control of 50Ω. A 20Ω series resistor is added to all input and output channels; along with the internal series resistance, it can provide 50Ω impedance matching with external equipment such as function generators or oscilloscopes.
Okay, that was some background about isolators, the Analog Devices isolators, and the evaluation board MAX2256CA. Let's do some experiments with the MAX2256CA evaluation kit.
I made the following experimental setup for testing the MAX2256CA kit. I used two separate power supplies for providing power to sides A and B though I provided the same voltage to both sides. For feeding input to the isolator I used a function generator and for observing the output I used a 200MHz RIGOL digital oscilloscope.
The following image shows the connections of the instruments with the evaluation kit.
I tested the isolator with square waves of different frequencies and observed the responses. I included a few screenshots of the oscilloscope.
I was very pleased with the response of the isolator. I did not notice any lag or distortion of the output compared with the input. I observed the distorted signal in the MHz scale, which was due to the limitation of my oscilloscope and signal generator. Though I was experimenting with the digital isolator, I was curious about the response with the analog input. So, I applied sinusoidal input to the isolator. Surprisingly, the response was like a comparator which is shown in the following figure. I also applied triangular waves and some arbitrary noise. The recorded screenshot is illustrated below.
Waveshape screenshot with some analog input:
Rising and falling of the signals:
To find any phase difference I used another oscilloscope because my previous oscilloscope is not capable the measure the phase difference (I did not get that option). First I applied 1a 100Hz signal to A0 and for the input I did not find any face difference between input and output signal.
From the screenshot above, the phase difference is exactly zero. I increased the frequency gradually and noticed very little phase difference for a high-frequency signal.
As the frequency increased the phase difference was also increased. I also tried to measure the time delay between the rising edge of the input signal and the rising edge of the isolated signal but did not find any considerable and stable time delay. Most of the cases it was around 100ns.
I applied 1.5 V on both sides of the isolator from the power supply. Then I applied a PWM signal of the same amplitude to the A0 of the isolator. I did not get any output from the isolator.
I don't know anything about the overvoltage tolerability of the isolator. So, I did not take any risk applying overvoltage.
