When a thermal shutdown occurs, the associated device channel shuts off and implements a retry protection mechamism to improve system reliability. Figure 8-20 explains how the affected channel responds depending on the load current and duration of the overcurrent event.

For load current lower than current limit, device enters into infinite thermal shutdown retry cycles phase until the device recovers from the thermal shutdown fault. In this case, the device turn off time depends on cooling time needed with inherent 200μs delay.

Figure 8-19 Device Enters Into Infinite Thermal Shutdown Retry Phase For Load Current (22A electronic load) Less Than Current Limit (ILIM = GND)

For load current higher than current limit, device implements a finite retry cycles phase protection mechanism based on the duration of the overcurrent event, that can trigger when either of the below fault conditions occur:

1. Absolute thermal shutdown (T_ABS): T_J,FET > T_ABS

2. Relative thermal shutdown (T_REL): T_J,FET – T_J,CONTROLLER > T_REL

3. Circuit Breaker (I_CB): A fast-trip protection that triggers when current exceeds the I_CB threshold during a hot-short condition. This quickly turns off the channel to protect the internal MOSFET.

The finite retry cycles phase protection mechanism has below durations:

1. Initial Retry Window (t < t_{RETRY_WINDOW}):

   • After I_CB or thermal shutdown triggers.
   • Retry attempts occur every t_{RETRY, INT} minimum duration.
   • Each retry can start with I_CB peak followed by current limit (I_CL) peaks.

2. Extended Overcurrent Window (t > t_{RETRY_WINDOW}):

   • Limited to 6 retry attempts.
   • First retry cycle happens with minimum t_{RETRY, EXTD}/2 duration.
   • Successive 5 retry cycles happen with minimum t_{RETRY, EXTD} duration.
   • Current peaks are typically limited to I_CL.

3. Latch-off Condition:

   • After 6 unsuccessful retry attempts.
   • Requires ENx pin toggle to reset.

In any of the above retry cases the relevant channel restarts when the conditions shown below are fullfilled.

1. Temperature Recovery: the T_ABS or T_REL to recover below the T_HYS level to restart the device.
2. Retry Window: For I_LOAD > I_CL, appropriate t_{RETRY_WINDOW} interval must elapse.

In case of I_LOAD > I_CL, if the retry timer has expired and the temperature of T_ABS or T_REL has not recovered below the T_HYS level, the channel does not retry until the temperature falls below the T_HYS level. Once a channel latches off due to an extended overcurrent event, the ENx pin can be brought from high to low (with minimum pulse duration of about 20us) to reset the FLT and SNS signal. The output of the channel then follows the ENx pin after the initial toggle from high to low.

Figure 8-20 Retry Protection Mechanism

Figure 8-21 and Figure 8-22 below shows how the device retries after a hot-short with and without thermal regulation, respectively. When the device experiences a thermal fault and enters the retry cycle, the first current peak in initial retry window reaches I_CB threshold, triggering fast trip circuit breaker. Successive current peaks are lower and correspond to set current limit (I_CL) value.

Figure 8-21 Retry Behavior After Hot-Short with Thermal Regulation

Figure 8-22 Retry Behavior After Hot-Short with No Thermal Regulation

In case the device enters inite retry cycles phase protection mechanism due to I_CB fault without thermal shutdown fault, the device can stay in thermal regulation in initial retry window and directly enter thermal shutdown retry behavior in extended retry window. Figure 8-23 shows this behavior where the finite retry cycles phase protection mechanism is triggered by I_CB fault.

Figure 8-23 Device Entering Into Extended Retry Window with Thermal Regulation Behavior in Initial Retry Window