A high-accuracy current limit allows higher reliability, which protects the power supply during short circuit or power up. Also, a high-accuracy current limit can save system costs by reducing PCB traces, connector size, and the capacity of the preceding power stage.

Current limit offers protection from over-stressing to the load and integrated power FET. Current limit holds the current at the set value, and pulls up the SNS pin to V_SNSFH and asserts the FAULT pin as diagnostic reports. The three current-limit thresholds are:

• External programmable current limit -- An external resistor, R_ILIM is used to set the channel current limit. When the current through the device exceeds I_{LIM_REG} (current limit threshold), a closed loop steps in immediately. V_GS voltage regulates accordingly, leading to the V_DS voltage regulation. When the closed loop is set up, the current is clamped at the set value. The external programmable current limit provides the capability to set the current-limit value by application.

  Additionally this value can be dynamically changed by changing the resistance on the ILIM pin. This can be seen in the Applications Section.

• Internal current limit: I_LIM pin shorted to ground -- If the external current limit is out of range on the lower end or the I_LIM pin is shorted to ground, the internal current limit is fixed. To use the internal current limit for large-current applications, tie the I_LIM pin directly to the device GND.
• Internal current limit: I_{LIM_REG} pin open -- If the external resistor is out of range on the higher end or the ILIM pin is open, the current limit reverts to half the nominal current limit range. This level is still above the nominal operation for the device to operate in DC steady state but is low enough that if a pin fault occurs and the R_ILIM opens up, the current does not default to the highest rating and put additional stress on the power supply.

Both the internal current limit (I_lim,nom) and external programmable current limit are always active when V_S is powered and EN is high. The lower value one (of I_LIM and the external programmable current limit) is applied as the actual current limit. The typical deglitch time for the current limit to assert is 2.5 µs.

Note that if a GND network is used (which leads to the level shift between the device GND and board GND), the ILIM pin must be connected with device GND. Calculate R_LIM with Equation 2.

For better protection from a hard short-to-GND condition (when V_S and input are high and a short to GND happens suddenly), an open-loop fast-response behavior is set to turn off the channel, before the current-limit closed loop is set up. With this fast response, the device can achieve better inrush-suppression performance.

For more information about the current limiting feature, see Section 8.3.5.1.