Reverse polarity protection for automotive NMOS LDO

ICs designed for automotive applications should withstand accidental reverse polarity caused by misconnection of their supply lines to the car battery. The reverse protection circuitry should avoid damages to both the IC and the system the IC is connected to. In particular, a large power dissipation while in reverse polarity situation is to be avoided. A simple solution is to insert diodes between the supply lines and the IC supply pins but this cannot be applied to linear low dropout regulators (LDOs)This paper presents two reverse polarity protection solutions for LDOs with NMOS power transistors. Starting from a circuit based on bipolar transistors, the proposed solutions can be implemented in low-cost CMOS processes. One of them also requires far less die-area Simulation results presented in the paper validate both proposals.