P-FET based reverse polarity protection is a very commonly used scheme in automotive applications to achieve low insertion loss protection solution. A low loss reverse polarity protection solution can be realized using the LM74501-Q1 with an external N-FET to replace P-FET based solution. The LM74501-Q1-based reverse polarity protection solution offers input TVS-less performance during ISO7637-2 pulse 1 event, better cold crank performance (low VIN operation) and smaller solution size compared to P-FET based solution. Figure 9-1 compares the performance benefits of LM74501-Q1 + N-FET over a traditional P-FET based reverse polarity protection solution.

• As shown in Figure 9-1, a given power level LM74501-Q1 + N-FET solution can be 50% smaller than a similar power rated P-FET solution.
• The second advantage that the LM74501-Q1 offers over a traditional P-FET is TVS-less operation for the body control module load driving paths where reverse current blocking is not a must-have feature and output loads are capable of handling negative voltage and reverse current for a short duration of the time.
• As PFET is self biased by simply pulling its gate pin low, P-FET shows poorer cold crank performance (low VIN operation) compared to the LM74501-Q1. During severe cold crank where battery voltage falls below 4 V, P-FET series resistance increases drastically as shown in Figure 9-1. This increase leads to higher voltage drop across the PFET. Also, with a higher gate-to-source threshold (V_T), this can sometimes lead to system reset due to turning off of the P-FET. On the other side, the LM74501-Q1 has excellent severe cold crank performance. The LM74501-Q1 keeps the external FET completely enhanced even when input voltage falls to 3.2 V during severe cold crank operation.