Electronic switch or smart switch (Smart Switch) is an intelligent device based on integrated circuit technology. It has the characteristics of small size, low power consumption, fast response speed and low impedance, which can provide highly reliable overcurrent protection. , Is an ideal replacement device for self-recovery fuses.
Taking AAT4610 as an example, its overcurrent protection can be completed within 1μs, and its response speed is 1 million times that of PolySwitch, which has a very obvious current limiting effect on transient peak current and surge current. Therefore, since the emergence of electronic switches, the development has been extremely rapid. Many companies have launched corresponding products, such as AAT4610 of AAT, MAX1946 of Maxim, μPD16875 of NEC, SL03-SL24 and SM03-36 of Microsemi, and Both USB02 and USB302 can be used for I / O port over-current protection.
Figure 1 AAT4610 pin definition We still take AAT4610 as an example to illustrate the working principle of electronic switch to achieve overcurrent protection. AAT4610 adopts SOT-23 plastic package (as shown in Figure 1), the definition of 5 pins is shown in Table 1.
The AAT4610 combines a 6V / 2A P-channel MOSFET field effect transistor with a gate driver, voltage reference, current limit comparator, and undervoltage lockout circuit in a SOT-23-5 package (see Figure 2). Among them MOSFET is an electronic switch, its on-off is controlled by the output voltage of the comparator, if the output current is greater than the set current, the operational amplifier AMP outputs a negative voltage, turns off the MOSFET, stops the voltage output, and plays a protective role in the power supply circuit. The maximum channel resistance of the MOSFET is only 180mΩ, and the quiescent current in shutdown mode is 1mA. The operating voltage of the MOSFET is 2.7V to 5.5V. When the input voltage is lower than 2.7V, the MOSFET is turned off by the undervoltage lockout circuit, and the power supply circuit is undervoltage protected.
Figure 2 AAT4610 internal logic block diagram The application circuit of AAT4610 is very simple. As long as two filter capacitors and a resistor RSET are connected externally, the overcurrent protection function can be realized, as shown in Figure 3. The filter capacitor is connected to the input and output of AAT4610 to eliminate the working noise of the electronic switch, and the current limiting resistor RSET is used to set the protection current value. When the working current exceeds the protection current value, the output voltage immediately drops to 0 volts, and its response time is about 800ns. Pin 4 is the enable terminal, input a voltage above 2.5V from the outside to make it work, otherwise AAT4610 will not protect.
Figure 3 AAT4610 application circuit
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