https://ezchina.analog.com/message/13081
In industrial automation control applications, serial communication is very important, and isolation of serial communication is even more important. At present, there are three commonly used solutions: first, serial port chip + external serial port isolator; second, dedicated serial port isolation chip + isolated power supply, such as ADI 's ADM3251 ; third, serial port chip + digital isolator + isolated power supply. In practical applications, the cost of the first two solutions is higher than the cost of the third solution, so I adopted the third serial isolation communication solution in the latest industrial control board, the serial port chip MAX232 + digital isolator ( ADum1201 ) + isolation For the power supply (5V-5V) solution, the cost of the entire chip is about 25 yuan, which is convenient to purchase. Let's talk about the key part of the solution -- the digital isolator- ADuM1201.
The ADuM120x are dual-channel digital isolators using Analog Devices ' iCoupler® technology. Combining high-speed CMOS with monolithic transformer technology, these isolation devices offer outstanding performance characteristics over alternatives such as optocouplers. iCoupler devices do not use LEDs and photodiodes, so there are no design difficulties typically associated with optocouplers. The simple iCoupler digital interface and robust performance characteristics eliminate the current transfer ratio uncertainty, nonlinear transfer function, and temperature and lifetime effects typically associated with optocouplers. These iCoupler products do not require external drivers and other discrete components. In addition, iCoupler devices consume only 1/10 to 1/6 the power consumption of optocouplers at comparable signal data rates . The ADuM120x isolators provide two independent channels of isolation and support multiple channel configurations and data rates (refer to the Ordering Guide ) . Both devices operate from a 2.7 V to 5.5 V supply voltage on either side, are compatible with low voltage systems, and support voltage translation across the isolation barrier. Additionally, the ADuM120x have low pulse width distortion ( CRlevel less than 3 ns ) and tight channel-to-channel matching ( CR level less than 3 ns ) characteristics. Unlike other optocouplers, the ADuM120x isolators have a patented refresh feature that ensures DC correctness in the absence of input logic transitions and power-up / power- down conditions. Applications of ADum1201 : 1. Multi-channel isolation where size is critical; 2. SPI interface / data converter isolation; 3. RS -232/RS-422/RS-485 transceiver isolation; 4. Digital field bus isolation; 5. Hybrid vehicles, battery monitors and motor drives.
The block diagram of the ADuM1201 is as follows:
Because it is a voltage-type device, it does not require an external current limiting resistor and a waveform shaping 74 logic chip as an auxiliary like an optocoupler. It only needs to place two 0.1uF decoupling capacitors near two different voltage pins . Makes the application circuit very simple and easy to use. Because its maximum communication speed can reach 25MBPS, it is also much higher than the high-speed optocoupler we usually use such as 6N137 .
In the sample test process, the serial communication isolation effect is very good, and there is no problem in the process of small batch use. Now I can say that I am very satisfied with ADI 's isolation products, thank you ADI ! The following is the actual circuit of the serial isolation communication part. Let's take a look. In the later stage of isolation products, we will continue to use ADuM series isolation chips.
