A high-accuracy adjustable current limit allows higher reliability, which protects the power supply and wires during short circuit or power up by being programed to an acceptable level. Also, current limiting can save system costs by reducing PCB traces, connector size, capacity of the preceding power stage and possibly reducing wire gauge.

Current limit offers protection from over-stressing to the load and integrated power FET. the current limit regulates the output current to the set value, asserts the FLT pin, and pulls up the SNS pin to V_SNSFH if the device is set up to output that channel on the SNS pin.

• The device can be programmed to different current limit values through an external resistor on the ILIM pin. There are 10 current limit settings which can be set based on resistors values in Table 6-1. ≤1% tolerance resistors should be used for R_ILIM resistor.
  Table 6-1 Current Limit Setting Through External Resistor

  ALLOWED RESISTOR VALUE(1)	ILIM THRESHOLD
  57.6kΩ	250mA
  43.2kΩ	500mA
  31.6kΩ	750mA
  23.2kΩ	1A
  16.5kΩ	1.25A
  9.76kΩ	1.5A
  4.87kΩ	1.75A
  2.49kΩ	2A
  Short to GND (<1.1kΩ)	2.25A
  Open (>60 kΩ)	5A

To set a different inrush current limit and steady state current limit, the current limit resistor can be changed dynamically when the device is ON. MOSFET based control scheme can be adopted for changing the current limit on the fly. However, the components and the layout at ILIM pin need to be considered carefully to minimize the capacitance at the pin. Any capacitance ≥ 100pF at ILIM pin might affect the current limit functionality. MOSFET with low input capacitance needs to be selected for dynamic current limit.

A current limit event occurs when I_OUTx reaches the regulation threshold level, I_CL. When I_OUT reaches the current limit threshold, I_CL, the device can remain enabled and limit I_OUTx to I_CL. When the device remains enabled (and limits I_OUT), thermal shutdown may be triggered due to the high amount of power dissipation in the FET. The regulation loop response when the device is enabled into a short circuit is shown in Figure 6-7. Please note that the current may peak at a higher value (I_{CL_ENPS}) than the regulation threshold (I_CL).

When an over-current event occurs, the current limit must respond quickly in order to limit the peak current seen on short circuits (both hot and enabling into a short). The peak has to be limited to ensure that the supply does not droop for a given amount of supply capacitance. This is especially important in applications where the device is powered from a DC/DC instead of car battery.

Figure 6-7 Enable Into Short Current Limit

However, a higher (I_{CL_LINPK}) output current than the current limit regulation loop threshold (I_CL) may be available from the switch during an overload condition before the current limitation is applied.

Figure 6-8 Linear Peak From Soft Short

The device applies a strong pulldown to limit the current during the short circuit event while the switch is enabled. The current will then drop down to zero before the current limit regulation loop engages and the switch turn-on and the behavior will be similar to the enable into a short circuit case.

Figure 6-9 Hot Short Event