Design Of The Protection Circuit In 28V/1.8A Smart Power Switch

Smart power switch circuit has a comprehensive protection function, which can work in a variety of harsh environments. It’s important to reduce the volume, and power consumption and offer good versatility. At present, discrete power output and protection module which are achieved by discrete devices has some disadvantages, such as large volume, high power consumption and low reliability. It isn’t able to meet the growing number of applications. In this thesis, a 28V/1.8A smart power switch chip has been designed.The design goal of smart power switch circuit is suitable for 4.9V-52 V wide input range, the RDS(ON) of power MOSFET is 0.22Ω, operating temperature range is-50 oC ~150 oC, has overvoltage and undervoltage protection with auto-restart and hysteresis, short circuit protection, as well.During the circuit design process, first, the author analyzes the design requirements and targets of the smart power switch, then introduce the overall structural and the working principle of the chip. Finally, the author design and simulate the overvoltage and undervoltage protection, thermal shutdown, short circuit protection and open load detection in off-state.Based on the working principle of the protection circuits, the author simulated the whole circuit by Cadence Spectre. The simulation results show that the on-state resistance is 81mΩ; the turn-on time is 20μs, the turn-off time is 86μs; It has fast demagnetization of inductive loads in off-state; thermal shutdown temperature is 160 oC, and thermal hysteresis is 7oC; overvoltage shutdown is 57 V, overvoltage hysteresis is 5V; undervoltage shutdown is 4.1V; short circuit shutdown voltage(Vbb to OUT)is 4.4V. The simulation results meet the design goal.Finally, based on 0.35μm BCD process, the author and team mates completed the layout design.