A capacitor connected from the ILTIMER pin to GND determines the programmable current limit fault time duration. The ILTIMER pin will charge the capacitor to 0.5 V during an overload condition and will discharge it otherwise through an internal pull down resistance. The time that the device will be in current limit before turning off is configured by C_ILTIMER and the time can be calculated using Equation 9. Connecting this pin to VIN will cause the device to be disabled once the internal current limit timer expires as shown in Figure 7-5. However, connecting it to GND will disable the internal timer functionality completely and therefore, in the case of a short, the device will remain at the programmed current limit indefinitely. When using the internal timer, the programmable current limit may not have time to settle to its programmed value. Because of this, the programmable current limit could briefly fall outside of its defined accuracy threshold. The fast trip off current limit, however, will remain valid.

Equation 9.

The time that the device remains disabled after the current limit timer expires is configurable through a capacitor connected from the RTIMER pin to GND. The RTIMER pin will charge the capacitor to 0.5 V after the switch is turned off and will discharge it otherwise. The time can be calculated using Equation 9. Connecting this pin to GND will keep the device disabled and it will require the device to be enabled by cycling the EN pin (Refer to EN Signal Low Time to Restart Device (t_LOW)). The behavior of the ILTIMER and RTIMER pins for a soft short, hard short and internal timer conditions are shown in Figure 8-2, Figure 8-3, and Figure 8-4, respectively. Please notice that Figure 8-2 and Figure 8-3 assume the fault is not present after the switch has been disabled and enabled again (retry mode). If the fault is present after the retry mode, the device will go into current limit mode and this cycle will repeat until the fault is no longer present.

Table 8-1 and Table 8-2 summarizes the fault duration time and retry time based on the pin conditions.

Figure 8-2 Soft Short Programmable Fault Timer Operation Connecting Capacitors to ILTIMER and RTIMER Pins

Figure 8-3 Hard Short Programmable Fault Timer Operation Connecting Capacitors to ILTIMER and RTIMER Pins

Figure 8-4 Programmable Fault Timer Operation Using the Internal Current Limit Timer and Disabling the Retry Mode

The programmable fault timers, ILTIMER and RTIMER, should be set in such a way that the capacitor for one timer is discharged before the other timer expires to ensure proper operation. In the specific case of using the internal ILTIMER, the RTIMER capacitor should be sized such that it is discharged before the internal ILTIMER expires, assuming the fault is still present. Figure 8-5 shows a situation where this constraint is not met as the RTIMER is much larger than the ILTIMER and therefore, the C_RTIMER is not discharged before the C_ILTIMER reaches 0.5 V, which is when the ILTIMER will expire. In order to avoid this situation, the constraint shown in Equation 10 must be met. Using this equation, once a capacitor for a timer has been selected (C₁ in Equation 10), the maximum value for the capacitor of the second timer can be determined. The internal pull-down resistance for each of the timers can be found in the Electrical Characteristics: All Devices table. For the situation shown in Figure 8-5, C₁ and R_PD1 in Equation 10 correspond to the RTIMER.

Figure 8-5 Programmable Fault Timer Capacitors Constraint

Equation 10.