Several methods of ESD protection circuit

The generation and hazards of ESD When two objects collide or separate, electrostatic discharge will occur. ESD is the movement of static charges from one object to another. The movement of static charges between two objects with different potentials is similar to a small one at a time. The magnitude and duration of the discharge during the lightning process depend on various factors such as the type of object and the surrounding environment. When ESD has high enough energy, it will cause damage to semiconductor devices. ESD may occur at any time, such as plugging or unplugging cables or The human body touches the I/O port of the device or a charged object touches the semiconductor device. The semiconductor device touches the ground, and the electrostatic field and electromagnetic interference generate high enough voltage to cause electrostatic discharge ESD. ESD can be basically divided into three types, one is ESD caused by various machines, the other is ESD caused by furniture movement or equipment movement, and the third is ESD caused by human contact or equipment movement. All three types of ESD have effects on semiconductor devices. Production and the production of electronic products are very important. The use of electronic products is most vulnerable to the third type of ESD damage. Portable electronic products are particularly vulnerable to damage from human body contact with ESD. ESD generally damages the connected interface devices. The situation is that the device after being hit by ESD may not be damaged immediately, but the performance will decrease and the product will fail prematurely. When the integrated circuit IC is subjected to ESD, the resistance of the discharge circuit is usually very small, and the discharge current cannot be limited. For example, when a static-charged cable is inserted into the circuit interface, the resistance of the discharge circuit is almost zero, causing an instantaneous discharge spike of up to tens of amperes. The current flowing into the corresponding IC pin will cause the instantaneous high current to seriously damage the IC. The local heating heat may even melt the ESD of the silicon die. The damage to the IC generally includes the internal metal connection being burned and the passivation layer is destroyed. The transistor unit is burned. Bad. ESD can also cause IC deadlock LATCHUP. This effect is related to the activation of SCR-like structural units inside CMOS devices. The high voltage can activate these structures to form large current channels. Generally, the serial interface device from VCC to ground is locked. The current can be as high as 1 ampere. The dead current will remain until the device is powered off, but by then the IC is usually burned out due to overheating. There may be two problems that are not easy to be discovered after the ESD impact. General users and IEC testing organizations use traditional loops. These two problems are usually not detected by the way feedback method and the insertion method.

1 The receiver in the RS-232 interface circuit generates crosstalk to the transmitter. The ESD protection structure in the RS-232 interface circuit of similar products may fail to a certain waveform of ESD or a certain ESD impulse voltage, which may cause the receiver input terminal after an ESD strike. A path is formed between the output of the transmitter and the transmitter, which causes the receiver to generate an intermodulation diagram for the transmitter. If there is a disconnection circuit in the RS-232 interface circuit, it is easier to produce intermodulation after an ESD impact during the shutdown period. It causes communication failure and the transmitter still has output even when it is turned off, causing the turn-off failure to make the other party RS-232 in the receiving state.

2 The RS-232 interface circuit reversely drives the power supply. Some ESD protection structures in the RS-232 interface circuit may form a current path between the input terminal and the power supply Vcc after an ESD impact. Figure 2 Reverses its power supply Drive if the power supply does not have the ability to sink current. Generally speaking, there is a forward diode in the output loop of the power supply. This will cause the power supply voltage Vcc to increase and damage the RS-232 interface circuit and other circuits in the system because of the input end of the RS-232 interface circuit. The voltage between 5V and 25V makes it possible for Vcc to be greater than 9V, exceeding the maximum range of the power supply voltage and burning out the circuit. 2 ESD protection circuit ESD is generated when two objects collide or separate, that is, static charge moves from one object to another. Therefore, the most effective protection of ESD is that the dielectric isolation is to isolate the internal circuit from the outside by an insulating medium with a thickness of 1mm. Ordinary plastics such as PVC, polyester or ABS can protect 8KV of ESD, but the actual medium cannot have gaps and seams. Therefore, the creep of the material and the gap distance are very important. LCD displays, touch screens, etc. have very thick corners 12mm to isolate internal circuits. . The second effective method of ESD protection is to shield to prevent large ESD currents from impacting the internal circuit. ESD impacts the metal shielding shell in the first few milliseconds. The shielding shell voltage will be much higher than the protective ground voltage. The voltage of the shielding shell will drop with the transfer of ESD charges, so the initial There will be a secondary ESD impact on the internal circuit within a few milliseconds, so just using an external shield is not enough. It is also an effective method to suppress the ESD impact by using the internal circuit and the shielding shell to share the ground or isolating the internal circuit. Although the installation of optocoupler and transformer on the top can not completely eliminate the impact of ESD, the combination of dielectric isolation and shielding can well suppress the impact of EDS. The optocoupler and transformer are especially suitable for the power part of the signal path. The best isolation is the optical fiber wireless and infrared signal path Another protection method is to add a series resistance of a resistance-capacitance element to each signal line to limit the peak current. The capacitor connected to the ground can limit the instantaneous peak voltage. This is low cost but limited in protection. The destructive power of ESD is to a certain extent. The above is suppressed but still exists because the RC element cannot reduce the peak value of the peak voltage. It only reduces the slope of the voltage rise and the RC element can also cause signal distortion, which limits the length of the communication cable and the communication speed. The external resistor/capacitor also Increased circuit board area. Another widely used technology is the addition of a voltage transient suppressor or TransZorb? Diode. This protection is very effective, but there are still some disadvantages. The additional device will still increase the area of the circuit board. The capacitance effect of the protection device will increase the equivalent capacitance of the signal line. Higher cost TransZorb? Diodes are more expensive about 25 cents. Each typical 3 send/5 receive COM port requires 8 TransZorb? Diodes cost up to $2. An effective method is to use a serial with internal integrated ESD protection. Interface devices are more expensive than ordinary non-protective devices, but the increased cost is lower than the cost of external protective diodes. The internal integrated ESD, the protective circuit does not increase the equivalent capacitance of any input and output pins and saves Circuit board area Taiwan Goodtech has developed a patented integrated ESD protection technology in recent years and can provide a full range of ESD protection serial interface devices, including products that are fully compatible with standard devices. Taiwan Goodtech has also applied the same technology to The ESD protection capabilities of all these devices in analog switches and switch debounce products comply with 15kV IEC1000-4-2 Air gap discharge 8kV IEC1000-4-2 Contact discharge 15kV Human body model HBM test standard Device.

3 The ESD protection technology of Taiwan Goodtech Company. The ESD protection specified by the European Community has its own strict test standards. The ESD structure must be completely transparent in normal working mode. The ESD process must not be blocked. It must pass all relevant ESD test standards. 15kV ESD human body model Test standard 8kV ESD IEC 1000-4-2 Contact discharge mode test standard 15kV ESD IEC 1000-4-2 Air gap discharge mode test standard 4kV ESD IEC 1000-4-4 Electrical fast transient/burst mode test standard Among which IEC 1000- The main difference between 4-2 and 15kV human body model test standards is that the shock absorption current of IEC 1000-4-2 is more than 5 times higher than that of the human body model under the same peak current voltage. 4kV ESD IEC 1000-4-4 electrical fast transient The test standard for variable/burst mode is to simulate the arc discharge results of switches and relays. Taiwan's solid technetium devices can provide 4kV protection twice the 2kV index of the IEC 1000-4-4 standard. In the real world, the waveforms generated by ESD may be various. Regardless of the waveform, Taiwan's Gutech engineers designed a highly adaptable structure to provide ESD protection for the device.