10.19 Overcurrent Protection

For protection against load faults, the LMZ31704 incorporates output overcurrent protection. The overcurrent protection mode can be selected using the OCP_SEL pin. Leaving the OCP_SEL pin open selects hiccup mode and connecting it to AGND selects cycle-by-cycle mode. In hiccup mode, applying a load that exceeds the overcurrent threshold of the regulator causes the regulated output to shut down. Following shutdown, the module periodically attempts to recover by initiating a soft-start power-up as shown in Figure 30. This is described as a hiccup mode of operation, whereby the module continues in a cycle of successive shutdown and power up until the load fault is removed. During this period, the average current flowing into the fault is significantly reduced which reduces power dissipation. Once the fault is removed, the module automatically recovers and returns to normal operation as shown in Figure 31.

In cycle-by-cycle mode, applying a load that exceeds the overcurrent threshold of the regulator limits the output current and reduces the output voltage as shown in Figure 32. During this period, the current flowing into the fault remains high causing the power dissipation to stay high as well. Once the overcurrent condition is removed, the output voltage returns to the set-point voltage as shown in Figure 33.

Figure 30. Overcurrent Limiting (Hiccup)

Figure 32. Overcurrent Limiting (Cycle-by-Cycle)

Figure 31. Removal of Overcurrent (Hiccup)

Figure 33. Removal of Overcurrent (Cycle-by-Cycle)