ESD protector principle
There are several technologies for the protection of the circuit, when selecting the circuit protection components, if the designer chooses improper protective devices will only provide the wrong concept of security. The selection of circuit protection elements shall be determined in accordance with the conditions of the wiring to be protected, the available circuit board space, and the electrical characteristics of the protected circuit. In addition, understanding knowledge characteristics of element protection is also very necessary, need to be considered one of the most important factors is clamped voltage of the device. The clamping voltage is across transient voltage suppressors in ESD device (TVS) on the voltage, it is protected by IC strain voltage. Because the oxide layer is relatively thin in the IC circuit made by the advanced process technology, the gate oxide layer is more vulnerable to damage. This means higher clamping voltage will be protected in the IC devices have higher strain voltage, and increased the probability of failure.
A lot of protection components are designed to absorb large amounts of energy, due to the structural components or design also leads to having very high clamping voltage. The rheostat clamping voltage is too high, they can not provide effective protection of ESD. In addition, due to the high capacitance varistor they cannot provide protection to the high speed data lines. TVS diode is the key technology to solve this problem, it has become the key technology to protect portable electronic equipment.
TVS diode is a solid state device specifically designed to absorb ESD energy and protect the system from ESD damage. If used properly, the TVS diode will limit the voltage across the protected device just over the rated operating voltage, but it is far below the threshold voltage.
ESD protector application
1 bottom connector applications
Bottom connector design is widely used in mobile consumer products, the current market applications mainly for mobile phones, PDA, DSC (digital camera) and MP3 and other portable products.
Because it is a direct current circuit, high capacitance device can be used. This port may be subjected to high energy impact, you can choose to integrate the TVS and over current protection devices.
As shown in Figure 1, is portable product bottom connector protection circuit schematic diagram, the data line protection IC for NZQA5V6XV5T1, nzqa6v2xv5t1, NZQA6V8XV5T1, NZQA8V2XV5T1, NZQA5V6AXV5T1, NZQA6V8AXV5T1, MSQA6V1W5T2, SMF05T1 and NSQA6V8AW5T2.
These products are with 4 single-phase independent line ESD protection, including MSQA series, NSQA series and SMF05 package form is SC-88A, NZQA series of package form is SOT-553. Which NZQA5V6XV5 is 5.6v unidirectional TVs protection device; NZQA6V2XV5 is 6.2V unidirectional TVs protection device; NZQA6V8XV5 is 6.8v unidirectional TVs protection device; 6.8v one-way, Low Capacitance TVS protection device is NZQA6V8AXV5; bidirectional 14V type, Low Capacitance TVS is NUP4102XV6. TVs devices these SOT5xx package were according to 260 DEG C reflow temperature processing production process, in line with 100% lead-free and electrostatic discharge protection, than the traditional SC88 package reduce circuit board space for up to 36%, reduce 40% of its thickness, suitable for portable devices with strict requirements of circuit board space, such as mobile phone, digital camera, MP3 player.
2 RJ-45 (10/100M Ethernet network)

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RJ-45 interface is widely used in the network connection of the interface devices, the typical application is the 10/100M Ethernet network.
As shown in Figure 2, the RJ-45 data line protection is mainly applied to the A Morimi company‘s low capacitance transient voltage suppressor diode --SL05, the operating voltage is 5V. In fact, the company has a series of SLXX products, products from SL05 to SL24, working voltage covering 5V, 12V, 15V, 24V. In accordance with IEC 61000-4-2 (ESD) 15kV (air) 8Kv contact IEC 61000-4-4 (EFT) 40A 5/50ns IEC 61000-4-5 (lightning) 12a (8 / 20 US) standard, in addition to using in the LAN / WAN equipment, but also suitable for used in high speed data line protection, mobile phones and USB port protection.
3 Protection of video circuits
At present video frequency common output port design has D-SUB (Figure 3), DVI (28 lines), SCART (19 lines) and D-TERMINAL (the main Japanese products in use). Line of video data with high data transmission rate, data transfer rates up to 480mbps, some video data according to the transmission rate of more than 1G. So it is necessary to low capacitance LCTVS, it usually is a low capacitance diode and TVs diodes are connected in series and to reduce the capacitance of the whole line (less than 3pf) and meet the requirements of high speed circuit. ONSEMI semiconductor company‘s SRDA05-4 has a good low capacitance characteristics, can provide 4 way ESD protection, and its successor product SRDA05-6 can provide up to 6 road ESD protection. SRDA05-X series products are suitable for all high speed communication line protection.
4 SIM card data line protection
SIM card data line protection has been the focus of all the company‘s products, and specifically for the design of such ports ESD (TVS) /EMI/RFI protection in a chip device, fully embodies the chip device unlimited integration program.
According to different uses to select the device to avoid make the device work in its design parameters near the limit, the protected circuit characteristic and can withstand ESD shock characteristics of selected reaction speed is fast enough, the sensitivity is high enough the device, which to effectively play protection device is the key, another integrated devices of other functions also should be considered first.

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Many semiconductor manufacturers provides a variety of TVS diode package form, especially as SOT23 and SC-70, as well as the same size as the chip flip chip like miniature package, occupies only about 4.8mm2 position on the board, but can also protect a plurality of circuit. Recently many of the new products is more adapt to portable equipment for the high degree of integration and miniaturization requirements, the EMI/RFI/ESD integrated protection in a device, which can not only effectively reduced space, but also greatly reduce the cost and reduce the device procurement cost and processing cost, for also need to port the several protection functions, can be described as the designer‘s preferred (Figure 4).
5 USB protection
General ESD USB protection points up (Figure 5) and downlink (Figure 6) two cases. For USB 1.1 ESD protection down the main use of the NUF2101, uplink ESD protection using STF202 or NUF2221W1T2. These products that can meet the USB line terminal ESD protection, but also has a good filtering function.
6 audio / speaker data line protection
In the audio data line protection (Figure 6), as a result of the audio circuit signal rate is low, the requirements of the device capacitance is not too high, 100pF is acceptable. Some mobile phones designed to be combined with a microphone and a microphone, while others are separate lines. The former case can choose a single TVS, and then a case if the two loop is adjacent, you can use a multi TVS array, only one device can complete the two circuit protection.
7 button / switch
For the keys and switch circuit, the data rate of these circuits is very low, there is no special requirements for the device‘s capacitors, with ordinary TVS array can be competent.