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Design Plan Sharing:485Interfaceemccircuit Design(Two)

Auth:亿配芯城 Date:2019/11/8 Source:www.yibeiic.com Visit:25 Related Key Words: EMCCircuit 485interface
In the last article“Design plan sharing:485interfaceEMCCircuit design(One)”in,We introduced the principle diagramRS485interface6KVContent of lightning protection circuit design。In this article,We will introduceRS485Interface circuit layout and circuit design content。

 

1
RS485Interface circuit layout

 

Program characteristics:

 

(1)The protective device and filter components should be placed neatly and close to the interface position.,Follow the rules of filtering first and then filtering,Try to avoid twists and turns when you are walking。

 

(2)Common mode inductors and jumper capacitors are placed in the isolation barrier。

 

case analysis:

 

(1)Interface and interface filter protection circuit can not be routed around and can not place high speed or sensitive devices。

 

(2)The projection layer below the isolation tape should be hollowed out,No trace。
 
2
RS485Interface circuit design

 

 

Program characteristics:

 

(1)In order to suppress internal board noiseRS485Interface radiates outward,Also to enhance the immunity of the board to external interference.,inRS485Add filter components at the interface to suppress,Based on the size of the filter member,Interface;

 

(2)Capacitor can be selectively added in the isolation strip as a connection between two grounds。capacitanceC4、C5The value is recommended as1000pF,Series common mode inductance on the signal lineCMCapacitance filtering,And connected in parallel with the interfaceGDTwithTVSPipe protection;And all guards are placed close to the interface,Common mode inductanceCMPlaced in the isolation belt,The specific layout is as shown above。

 

case analysis:

 

(1)When there is a poorly compatible or incompatible circuit between the interface and the board,Need to be performed between the interface and the board.“Divided”deal with,That is, according to different port voltages、Level signal and transmission rate to set the ground line。“Divided”,Can prevent the superposition of the return signal of incompatible circuits,Prevent common ground impedance coupling;

 

(2)“Divided”Phenomenon causes the impedance of the return signal to rise across the isolation band,Causing greatEMCrisk,Therefore, a capacitor is used to provide a return path to the signal between the isolation strips.。
 
related information:
Design plan sharing:485interfaceEMCCircuit design(One)

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