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Digital isolators that improve circuit safety and quality include magnetic isolation methods and capacitive methods.
When making a selection, many people may be researching to find out the differences and features between the two, or to decide which one is suitable for their application.
This time, the second part of the two-part series, we will introduce the lineup of the former Maxim company using the capacitive method. Please refer to it.
Review of the first part: Types and differences of digital isolators
In the first part, we introduced the differences between the magnetic insulation method and the capacitance method, the features of each, and examples of applications for which they are suitable.
Digital isolators have different strengths depending on the coupling method, insulation material, and encoding used. It is important to select the optimal type of digital isolator depending on the application.
As shown in the figure below, Analog Devices, Inc. has a lineup of both coupling methods.
If you want to know more, please read the first part as well.
→Click here for the first part [Digital isolator showdown (first part): Magnetism vs. capacitance]
In the first part, we introduced the lineup of magnetic insulation methods. This is an old Analog Devices product that uses polyimide as the insulation material and uses on-off keying for encoding.
This time, we will introduce the old Maxim lineup using the capacitive method.
[Lineup introduction/Part 2] Old Maxim capacitance method
The old Maxim capacitive lineup uses SiO2 (silicon dioxide) as the insulation material and edge trigger encoding. What features does this lineup have?
Key features include high data rates, low propagation delay, low jitter, and low power consumption. These are advantages not found in magnetic coupling methods using polyimide.
A detailed configuration diagram is shown below.
If we take a look at the specs that stand out from the product lineup, there are attractive numbers such as ``data rate up to 200Mbps,'' ``propagation delay of 10ns or less,'' and ``power consumption per channel of 0.65mA or less (at 1Mbps communication).'' to line up. The lineup is rich in features unique to the capacitive method.
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Data rate: up to200Mbps |
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Power consumption per channel at 1Mbps communication: 0.65mAor less |
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Propagation delay: 10nsor less |
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Jitter: 8ps |
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Channel-to-channel skew: 1ns |
Outstanding specifications of capacitive isolators (former Maxim lineup)
Why is "low propagation delay" important?
Why is low propagation delay important in digital isolators? Let me explain why.
Simply put, propagation delay is the delay from the input to the output inside a digital isolator.
For example, let's consider a case where SPI communication is performed between a microcontroller unit (MCU) and an A/D converter (ADC) as shown in the figure below, and a digital isolator is placed between them to isolate them.
The MCU sends the clock (SCLK) that is the sampling reference for the ADC, and the ADC responds to the MCU with the AD conversion results.
At this time, due to the propagation delay of the digital isolator in between, the ADC 's latch may not be executed at the appropriate timing, causing a discrepancy between the intended data and the obtained data.
To prevent deviations due to propagation delays, adjustments such as slowing down the ADC sampling rate may be necessary, forcing compromises from the ideal system design.
In particular, in applications that require high-speed sampling of light and sound, propagation delay specifications have a significant impact. Therefore, it is desirable that the propagation delay be as low as possible.
Why is "low jitter" important?
Another advantage of the capacitive type lineup is low jitter. How does jitter affect performance?
Jitter is timing fluctuation. From the perspective of A/D conversion, large jitter shifts the ACC sampling point, resulting in distortion and noise, which degrades the signal-to-noise ratio (SNR).
In particular, keep in mind that clock jitter is an important indicator for high-precision measurements.
[Lineup (1) MAX22445] Industry-leading high-speed 4-channel isolator
Now, let's introduce the specific lineup.
The MAX22445 4-channel isolator takes full advantage of the features of the capacitive method to achieve industry-leading high-speed data rates and low propagation delays. The maximum data rate of 200Mbps and jitter of 8psRMS are both noteworthy specifications.
・ High timing performance
-Max data rate: 200Mbps
-Low jitter: 8psRMS
-Low propagation delay: 10ns
-Low channel-to-channel skew: 2ns
・ Low power consumption
-Each channel 0.74mW (at 1Mbps communication, VDD=1.8V)
・Reinforced insulation
-Isolation voltage (VISO): 5kVRMS
-Continuous voltage resistance (VIOWM): 1500VRMS
-CMTI：50kV/µs
·easy to use
-Power supply voltage range: 1.71V to 5.5V
-Operating temperature range: -40℃ to +125℃
■ Application example
・Communication base station
・Applications that require high-speed and high-precision measurement of light, sound, etc.
Comparison with magnetic isolation method “ADuM341E”
What are the differences between the MAX22445 and the recommended magnetic isolation digital isolator "ADuM341E" introduced in the first part? Please see the comparison table.
Old ADI is better for robustness, old Maxim is better for timing performance and power consumption
Comparing data rates, the MAX22445 has a data rate of 200Mbps compared to the ADuM341E 's 150Mbps, allowing faster communication. Additionally, the MAX22445 has lower propagation delay, which indicates that it has an advantage in high-speed communications. The MAX22445 also consumes much lower power, approximately one-fourth the power of the ADuM341E.
On the other hand, the ADuM341E excels in reinforced isolation voltage and CMTI, which are indicators of robustness.
As you can see from the comparison table, the old Analog Devices lineup, which focuses on magnetic coupling methods, is suitable for applications that require the robustness of digital isolators. On the other hand, for applications requiring high-speed communication and low power consumption, the old Maxim lineup of capacitive devices is useful.
[Lineup (2) MAX22820] Ultra-low power consumption, 2-channel reinforced isolation isolator
The next product to be introduced is the MAX22820, which has an extremely low power consumption of 54.7 μA when communicating at 1Mbps. We have achieved specifications that are ideal for applications that place more emphasis on power consumption than communication speed. For example, it can be fully utilized for battery-powered IoT devices.
・Maximum data rate: 10Mbps
・ Ultra low power consumption(per channel,VDD=3.3V)
-11.4µA (DC)
-15.4μA (100kbps)
-54.7μA (1Mbps)
・Reinforced insulation
-Isolation voltage: 5kVRMS WSOIC package
-Isolation voltage: 3kVRMS NSOIC package
-CMTI：200kV/µs
·easy to use
-Power supply voltage range: 1.71V to 5.5V
-Operating temperature range: -40℃ to +125℃
■ Application example
・ IoT devices
・Portable measuring instruments
・Handy terminal
In this way, in the former Maxim 's capacitive lineup, some products have strengths in high-speed communication, while others have strengths in low power consumption. You can choose from a variety of products to suit your needs.
In the first and second parts, we introduced Analog Devices' digital isolators. Digital isolators have different features depending on the insulating material and coupling method, so it is necessary to select one that suits the application. We have a rich lineup, including old Analog Devices products with excellent robustness and old Maxim products with excellent power consumption and speed.
We hope that this article will help you choose the best digital isolator for your application.
Evaluation boards are available for both, so you can try them out right away.
If you have any questions, please feel free to contact us.
Application example
- Applications that require high-speed and high-precision measurements such as communication base stations
- Applications that require low power consumption such as portable instruments
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