Reverse current occurs when V_VS<V_OUT. In this case, current will flow from V_OUTx to VS. Reverse current can be caused by miswiring at the output, or a capacitive or inductive load can cause inverse current. For example, if there is a significant amount of load capacitance and the V_S node has a transient droop, V_OUTx may be greater than V_S. The V_Sdroop may be caused by inrush current from a different load. Similarly load/supply faults and inductive loads can cause supply to be pushed up as well. Another application is to provide protection when output connection to supply (miswiring) occurs when the input power supply is not available or connected. The device monitors V_S and V_OUT to provide true reverse current blocking when a reverse condition or input power failure condition is detected.

To prevent reverse current flow, TPS274C65AS integrates a NMOS gate driver that drives an external blocking FET. The blocking FET is enabled as soon as the device is enabled and V_VS > V_{S_UVP}. When a reverse current condition is detected such as V_OUT － V_VS > V_{RCB_R}, the blocking FET gets disabled to prevent unwanted reverse currents and signaled through RVRS_BLK_FLT and FLT. Once off, TPS274C65AS has the hysteresis implemented to keep the RCB FET off as long as V_OUT － V_VS < V_{RCB_F}. After t_{RCB_comp_reset} timer expired, the RCB FET is enabled to check if the reverse current condition has cleared, and the comparator threshold is reset from V_{RCB_F} to V_{RCB_R}. If V_OUT － V_VS > V_{RCB_R}condition is met after the RCB FET is re-enabled, TPS274C65AS again turns off the RCB FET. During reverse current event, current sensing is not available, and I_SNS and ADC register go to 0 mA.

In case the RCB FET needs to be kept off, the per channel RCB bit RCB_CHx can be turned low to keep the RCB FET off. However, the main FET needs to be off as well to avoid excessive heat through the RCB FET that can lead to the RCB FET damage. If there's no external RCB FET connected, RCB_DIS bit needs to be turned high , and the RCB pins need to be left floating. Each channel has RCB_CHx bit to configure the RCB FET to be always OFF or with normal RCB function as described above. Table 8-8 shows some example use cases for the RCB feature.

Figure 8-30 Reverse Current Blocking