Negative Input Protection Design of Power Switch

A design method is presented to protect the power switch from negative voltage at the input power supply due to the connecting or disconnecting the power line. To ensure proper power supply acquisition under positive input conditions and isolation under negative input conditions, a negative input isolation circuit is first used for the non-power circuit. Then, two protective NMOS transistors are used to pull the gate and substrate of the power NMOS transistor to the negative VIN to prevent leakage current in the power NMOS transistor. At the same time, two simple switches which conduct under positive VIN and cutoff under negative VIN are used to effectively turn off the two protective NMOS transistors, preventing them from affecting the normal multi-mode operation of the power switch during positive VIN. This circuit does not require an additional positive voltage power supply and does not introduce voltage drop, providing negative protection for all devices and circuits between VIN and GND as well as between VIN and VOUT. The proposed power switch is implemented using a 180 nm BCD process, and the test results show that the power switch can effectively mitigate -5 V negative voltage at the input power supply.

Recommended citation: Wan M, Wang Z, Ma Y, et al. Negative Input Protection Design of Power Switch[J]. IEEE Transactions on Circuits and Systems I: Regular Papers, 2025.
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