System anti electrostatic scheme for interconnection interface of Internet of things
Guang Liang Hu
(Shenzhen tage Electronic Technology Co., Ltd. Shanghai 200114)
Abstract: Aiming at the electrostatic threat encountered in the production and use of Internet of things products, the lightning protection and anti-static protection schemes of various typical interfaces are enumerated.
Keywords: Internet of things, interface protection, anti-static, ESD
1., the necessity of anti-static products of Internet of things
As following the Internet, mobile Internet technology revolution after another wave of things (Internet of Things) has undoubtedly become a battleground in the scientific and technological industry.
Intelligent home appliances of the future, to provide you with fresh, seasonal food and how to cook food; intelligent Home Furnishing, automatically according to ambient light conditions, adjust brightness or change their color to change the mood; intelligent atmosphere control, through the learning habits of residents are most effective use of energy for heating or cooling; intelligent wear, can automatic advice according to the mood of clothing, read the health parameters, provide advice and diet fitness activities to help people get a better health indicators; intelligent vehicle and traffic system, improve traffic efficiency and comfort, make highway travel more secure.
The Internet of things products provide a variety of new applications to meet the needs of digital environmental monitoring, including our own monitoring. However, it is frequent communication everywhere interaction, or the communication between people and equipment, equipment in communication at the same time, the information channel also opens the door to electromagnetic interference, the electromagnetic interference is the most common threat of electrostatic. At any time, the cable is in contact with the connector, or a person touches an electronic system, and there is a possibility of a charge transfer, which then results in an electrostatic discharge process.
2. test standard for electrostatic discharge
Figure 1: ESD curve
Reverse reverse voltage (cut-off voltage) VRWM and reverse leakage current IR: reverse breaking voltage (cut-off voltage) VRWM represents the maximum voltage at which the TVS diode is not connected. At this voltage there is only a small reverse leakage current of IR.
Breakdown voltage VBR:TVS/ESD through the specified test current IT voltage, which is indicative of the TVS tube conduction voltage.
The pulse peak current IPP:TVS/ESD maximum peak current 10/1000 S wave through the (peak current 8/20 S wave is about 5 times, the 8/20 s is defined as the IPP pulse current, please refer to figure 3), more than the current value may cause permanent damage. In the same series, the higher the breakdown voltage, the smaller the peak current allowed to pass through the pipe.
The voltage at which the maximum clamp voltage VC:TVS/ESD flows across the pulse peak current IPP.
Forward conduction voltage VF:TVS/ESD, voltage through forward conduction current IF.
Figure 3: surge 8/20 mu S current waveform

Understanding the characteristics of the TVS/ESD curve, it is clear that the task of TVS/ESD is to occur ESD event, the input voltage is maintained within the safe overvoltage range, and in normal operation does not affect system performance. The TVS/ESD is placed adjacent to the ESD event and may enter the system position to limit the voltage at the sensitive node and lead the current to a less sensitive node, such as the ground level. To achieve this function, the ESD diode must have high impedance in normal working voltage range, low impedance in addition to the normal working voltage range, so as to be directly from the current sensitive nodes off, and limit the transient voltage, so as to guarantee that the system of anti-static reliability.
4. antistatic circuit design
4.1 parallel ESD protection device at the interface of the circuit
As shown in Figure 4, the most effective way is at the entrance of the parallel ESD diode interface, because ESD clamp characteristics in electrostatic discharge, electrostatic peak voltage is ESD diode clamp pressure within the specified scope, to ensure stable operation of the rear chip.
Figure 4:ESD diode operation principle
4.2 select the appropriate ESD protection device in the circuit
Select ESD electrostatic protection device, note:
Do not exceed the maximum allowable voltage clamping voltage protected device, circuit voltage does not exceed the device operating voltage protection, low capacitance, leakage flow may reduce interference and loss.
4.3 ESD protection device in the circuit location and ground wire settings
(1) the electrostatic protection device shall be installed as close as possible to the electrostatic input, away from the protected device;
(2) the earth wire that the ESD protection device must connect is not the digital earth wire;
(3) the line to the ground is as short as possible, and the distance between the electrostatic protection device and the protected line is as short as possible;
(4) try to avoid being protected and not protected line side by side line.
5. electrostatic protection case of Internet of things interface
Because of things many products, a variety of sensor signal acquisition and diversity, the main chip data processing and transmission are different, the company has developed a protection device for a variety of communication interface, also can choose single products according to the needs of the board.
5.1 Internet of things interface speed, parasitic capacitance and corresponding ESD protection device list
Things different requirements on the circuit parasitic capacitance of communication interface with different rates based on ESD and its parasitic capacitance diode is inevitable, so in different communication interfaces when selecting ESD parasitic capacitance value of the products need to pay special attention to the following list, the type used for various communication interfaces and restrictions on ESD consolidation rate the capacitance of the diode and protection scheme for communication interface.

序號	接口名稱	傳輸速度（Mbit/S）	對電路寄生電容要求（pf）	推薦保護器件
				一級保護	二級保護	三級保護
1	USB2.0接口	480	<3			SR05/SRV05-4
2	USB3.0接口	4800	<1			LC05CD
3	USB3.1接口	10000	<0.5			ULC3324P10 ULC052010P5
4	TYPE-C接口	10000	<0.5			ULC3324P10 ULC052010P5
5	快充USB接口	480	<3			ULC1654N
6	快充電源接口	-	-			ESD1285P
7	100M網絡接口	100	<5	3R090-5S	HL60-025	SLVU2.8-4/SRV05-4
8	1000M網絡接口	1000	<1	3R090-5S	HL60-025	LC3311CCW
9	10000M網絡接口	10000	<1	3R090-5S	HL60-025	ULC0542T
10	POE網絡接口	100	<5	3R090-5S	HL60-025	SLVU2.8-4 SMCJ68CA
11	HDMI1.3接口	10200	<1			ULC0524P
12	HDMI1.4接口	10200	<1			ULC0524P
13	HDMI2.0接口	18000	<0.5			ULC0514P10 ULC0544P10
14	DISPLAY視頻接口	5400	<1			ULC0524P
15	VGA模擬視頻接口	162	<1			ULC0524P
16	DVI數字視頻接口	3960	<1			ULC0544M
17	Audio音頻接口	1.5	<100			SDA05W5/ULC0511CDN
18	LVDS接口	655	<10			ULC0524P
19	SIM卡接口	7.2	<10			SRV05-4
20	SD卡接口	10	<10			SRV05-4
21	MMC卡接口	10	<10			SRV05-4
22	E-SATA接口	6000	<1			ULC0524P
23	I2C接口	3.4	<100			SDA05CW SD05C
24	T1 E1接口	1.544	<100	P2300SC	HL250-120	SRV05-4
25	RS232接口	0.2	<50			SD12C SMC12
26	RS485接口	10	<50	3R090-5S	SMD1812P050TF	SM712
27	CAN總線接口	1	<50	3R090-5S	SMD1812P050TF/24	SMC24 SD24C
28	LIN總線接口	1	<50	3R090-5S	SMD1812P050TF	SMC24 SD24C
29	xDSL接口	2	<100			SR70
30	RF /GPS天線接口	1000	<1	SMD4532-090		ULC0511CDN
31	GPIO接口	5	<100			SDA05W5 SD05C
32	5V直流電源接口	-	<1000			SMBJ5.0CA SMCJ5.0CA
33	12V直流電源接口	-	<1000			SMBJ12CA SMCJ12CA
34	48V電源接口	-	<1000			SMCJ48CA
35	12V汽車電源口	-	<1000			SMCJ22CA SM8S22A
36	24V汽車電源口	-	<1000			SMCJ36CA SM8S36CA
37	220V交流電源接口	-	<1000	2R600-8L	20D561KJ

A variety of networking interfaces listed in the table, a tage electrostatic protection scheme corresponding interface, convenient reference design, if necessary, please contact the author.
6., Internet of things interface, electrostatic protection, development direction
Internet communications networking industry help arranged in a crisscross pattern, 4 and 5 industrial air plant for faster, more stable, and more simple. Typical interconnection interfaces and IC continue to come out of the old, the pursuit of smaller size, more lines, more sophisticated. Anti electrostatic ESD follow the evolution of the interface IC, do the corresponding match, ESD volume will become smaller, lower capacitance, anti surge ability more flexible line more flexible.
Reference
[1] PCB anti ESD design authors: Jiang Airu
ESD protection design for [2] electronic communication products: Wang Yuanyuan, Zhang Yao
[3] EMC baiwenbaida Author: Xu Qianghua
Author: Hu Guangliang, senior engineer, engaged in research and development of ESD components and circuit anti-static design!