The LM5067 monitors the current in the external MOSFET (Q1) by measuring the voltage across the sense resistor (R_S), connected from SENSE to VEE. The required resistor value is calculated from:

Equation 2.

where

• I_LIM is the desired current limit threshold

When the voltage across R_S reaches 50 mV, the current limit circuit modulates the gate of Q1 to regulate the current at I_LIM. While the current limiting circuit is active, the fault timer is active as described in the Fault Timer and Restart section. For proper operation, R_S must be no larger than 100 mΩ.

While the maximum load current in normal operation can be used to determine the required power rating for resistor R_S, basing it on the current limit value provides a more reliable design since the circuit can operate near the current limit threshold continuously. The resistor’s surge capability must also be considered since the circuit breaker threshold is approximately twice the current limit threshold. Connections from R_S to the LM5067 should be made using Kelvin techniques. In the suggested layout of Figure 9-2 the small pads at the upper corners of the sense resistor connect only to the sense resistor terminals, and not to the traces carrying the high current. With this technique, only the voltage across the sense resistor is applied to VEE and SENSE, eliminating the voltage drop across the high current solder connections.

Figure 9-2 Sense Resistor Connections