ADuM Series Magnetic Coupling Applications (ADI Data)

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ADuM Series Magnetic Coupling Applications (ADI Data)

This article starts from the basic reasons and applications of isolation, and describes why we should isolate and when to isolate in the system application of various circuits. It also briefly describes the basic principles of magnetic coupling digital isolators introduced by Analog Devices, Inc. (ADI) and their applications in various circuit isolation applications.

I. About isolation

1. What is isolation? Why is it isolated? Under what circumstances do you need to do an isolated design? The definition of electronic electricity is: a method to prevent current flow between two communication points. The simple point is that there must be signal transmission between two points but no current flow.

The main reason for isolating the circuit is that isolation is a way to prevent current from flowing between the two communication points. Generally, isolation techniques are used in two cases:

The first case is:

It is the application of high voltage or high current in the circuit that may damage the equipment or endanger the operator. Medical applications, motor control, bus isolation, I/O isolation, etc.

The second case is:

Generally, when multiple systems are interconnected, there is a potential difference between the grounds of different systems. At this time, if we do not separate the two grounds, a ground loop will be formed, which will interfere with the whole system. So it must be isolated.

In both cases, isolation is used to avoid current flow, while data or power transfer between the two points is allowed.

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Our general industrial control system, motor control system, and bus communication system are all transmitted by the main control chip (microcontroller, ARM, DSP, etc.) through the interface and the controlled system, and the application environment of the controlled system is often complicated. There will be high voltage, lightning strikes, high currents, etc., and if they are directly connected to the main control system, these dangerous signals may destroy the entire system, which is extremely harmful to the entire application system. Therefore, we must take safety isolation into account when designing the circuit.

Second, where is the general application of isolation:

Isolation is commonly used in applications involving high voltage, high speed or high precision communication and long distance communication.

Common applications are:
ν Industrial I/O systems ν Interface aspects ν Power supply ν Motor control instrumentation We can find these applications in a wide range of market segments, including:
ν Medical equipment ν
ν Communication Network ν Plasma Display Hybrid Electric Vehicle Equipment

3. What are the parameters involved in isolation?

There are many parameters that measure the isolation characteristics of an insulator, including:
ν isolation rating
ν insulation voltage

Instantaneous suppression (common mode suppression)

In general, the commonly described parameters for the isolation capability of an isolation device are the isolation voltage and the isolation voltage. In addition, the transmission communication capability of the signal between the isolation barriers is measured by the transient suppression capability. The three parameters will be described one by one below.

1. What is the isolation voltage?

The isolation rating of the isolation device is a measure of the system's ability to resist common-mode voltages in a short period of time. Refers to the voltage value that the input and output of the device are subjected to when they are shorted. Usually measured in terms of 60 Hz RMS, the device is capable of withstanding the high voltage between the input and the terminal output in one minute. The isolation voltage of a typical isolation device is 2.5KV RMS. Some devices will have this parameter of 3.75KV RMS or higher. The isolation voltage does not measure the ability of the device to withstand a safe voltage for long periods of time, which is described by the isolation voltage.

2. What is the insulation voltage?

The working voltage defines the maximum voltage that a device can withstand for a long period of time under steady state operation. It is typically from 100 to 600V RMS.

3. What is the transient common mode rejection capability?

The transient common-mode rejection of an isolator measures the transient common-mode effects between the input and output sections while maintaining proper signal transmission. Many isolation devices do not have a corresponding specification for this parameter, and the specified range is also from 5- to 25KV/μs.

Other important work parameters include:
ν Operating current, input signal current, and output drive current. ν
ν Transmission delay time ν Pulse width distortion: the difference between the output pulse width of the signal and the pulse width of the input signal. ν Transmission speed: Maximum signal data transmission speed that can be supported ν Operating voltage range: Operating voltage range of the power supply

Operating temperature: the temperature range over which the device operates

Which of the above working parameters is more important depends on the actual application of the user, and sometimes the important parameters in this system are sometimes not important in another system. There are other relatively important operating parameters that vary with operating temperature, power variation of the device, noise of the input signal, and DC input conditions or output conditions in the event of a power loss.

Second, ADUM series magnetic coupling introduction:

In the traditional isolation scheme, we generally use optocouplers, such as 6N137, TLP521, etc. The optocoupler is isolated by photoelectric conversion. The application time is relatively long and the scheme is mature. It is still the first choice of many circuit designers, but Similarly, optocouplers also have shortcomings and disadvantages such as insufficient speed, high power consumption, aging LEDs, and unstable use.

Magnetic coupling isolation technology has been developed in recent years. It uses chip-level transformer isolation technology. It adopts high-speed iCMOS technology and chip-level transformer technology, and has photoelectricity in terms of performance, power consumption, volume and speed. The advantages that isolation devices can't match. Below we take the ADUM1100 as an example to introduce the principle of magnetic coupling isolation technology. The following figure shows the principle block diagram of ADUM1100.

ADUM1100 block diagram


motor control



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