The TPSI310x-Q1 and TPSI313x-Q1 devices include one fault comparator that is used to quickly assert the output driver, VDRV, low to allow for the fastest disable time of the external power switch. This is useful for critical events such as over-current protection (OCP) to protect the external power switch and downstream circuitry. The block diagram of the fault comparator is shown in Figure 8-8. The TPSI311x-Q1 devices have two fault comparators. This can be useful for applications such as bi-directional OCP or whenever there are two independent critical events required to protect the external power switch. The TPSI312x-Q1 device does not support any fault comparators, only alarm comparators.

Figure 8-6 Fault Comparator Block Diagram

If the input voltage of the fault comparator, FLTn_CMP, exceeds the internal reference voltage, VREF, the comparator output asserts high. The comparator output is filtered and is adjustable via an external 1% resistor, R_RESP, connected from RESP to VSSS. The filtering of low-to-high transitions of the comparator output is adjustable by the external resistor. High-to-low transitions of the comparator output are filtered at a fixed setting. Filtering the comparator output allows for flexibility and application tradeoffs to help minimize false trigger events while still providing adequate protection. The filtered comparator output is then fed into the driver logic. If the comparator output low-to-high event passes through the filter, VDRV is immediately asserted low regardless of the state of EN. The TPSI310x-Q1, TPSI311x-Q1, and TPSI313x-Q1 fault comparators are not latched. If a fault condition is removed (FLTn_CMP voltage falls below the internal reference voltage and passes through the filter), VDRV is held low until the recovery timer has elapsed. Once the recovery timer has elapsed, VDRV follows the state of EN. If a fault condition occurs before the recovery timer has elapsed, the recovery timer is restarted.

The comparator output information is transferred to the primary side of the device via back-channel communication (BCC) over the isolation barrier. As shown in Figure 8-8, any low-to-high transition of the comparator output (fault event) that passes through the filter is extended to make sure the event is captured by the sample logic. Any high-to-low transition of the comparator output (recovery event) that passes through the filter are not extended. A recovery event can be missed by the sample logic if the event does not last longer than the sample period. Therefore, priority is given to fault events over recovery events. FLTn open-drain output is asserted low upon the fault event. If a recovery event occurs and is captured by the sample logic, FLTn open-drain output is set to high-impedance, but VDRV remains asserted low until the recovery timer elapses.

The TPSI310xL-Q1, TPSI311xL-Q1, and TPSI313xL-Q1 devices have latched fault comparators as shown in Figure 8-7. Fault events are latched and held until EN is asserted low. Upon a fault event, VDRV asserts low and is held until EN is asserted low and the recovery timer elapses. FLTn is also asserted low and held until EN is asserted low. If the fault event has recovered, FLTn is asserted high even if the recovery timer has not elapsed.

Figure 8-7 Latched Fault Comparator Block Diagram