The second method for setting the limit voltage is to connect the LIMIT terminal to a programmable DAC (digital-to-analog converter) or other external voltage source. The benefit of this method is the ability to adjust the current limit to account for different threshold voltages that are used for different system operating conditions. For example, this method can be used in a system that has one current-limit threshold level that must be monitored during the power-up sequence but different thresholds must be monitored during other system operating modes.

In Table 7-3, V_TRIP represents the overcurrent threshold the device is programmed to monitor for and V_SOURCE is the programmed signal set to detect the V_TRIP level. NAF is included in the V_SOURCE equation for the 10-µs delay setting. This value equals 500 µV and is adjusts the operating point for the noise in the delay setting. The 50-µs and 100-µs delay settings do not use the NAF term in calculating the V_SOURCE threshold. For these delay settings, the NAF term is omitted. See the Section 7.3.7 section for more details on the noise adjustment factor.

TI recommends using NAF in calculating the value for V_SOURCE at the 10-µs delay setting. Removing NAF from the V_SOURCE calculation at the 10-µs delay setting lowers the trigger point of the alert output. Lowering the trigger point results in the device issuing an overcurrent alert prior to reaching the corresponding V_TRIP threshold. The averaging effect included with the 50-µs and 100-µs delay settings inherently eliminates the effect internal noise has on the threshold voltage.