While the switch disabled and WB_OFF_CHx_EN high, an internal comparator watches the condition of V_OUT. The TPS274C65 includes a current source connected to V_OUT controlled by the DIA_EN signal. So, if the load is disconnected (open load condition) or there is a short to battery the V_OUT voltage will be pulled towards V_S. In either of these events, the internal comparator will measure V_OUT as higher than the open load threshold (V_OL,off) and a fault is indicated on the FLT pin and on the SNS pin. No external component are required in most cases, however if there is external pull-down resistor to GND on V_OUT, an additional external pull-up resistor might be necessary to bias V_OUT appropriately.

The comparator and detection circuitry is only enabled when EN = LOW. Open load will be indicated on the FLT pin even if WB_OFF_CHx_EN is set low, but will need an external pull-up resistor (and potentially a switch). Open load fault signaling on the SNS is enabled only if WB_OFF_CHx_EN is set HI.

While the switch is disabled, the fault indication mechanisms will continuously represent the present status. For example, if V_OUT decreases from greater than V_OL to less than V_OL, the fault indication is reset. Additionally, the fault indication is reset upon WB_OFF_CHx_EN = 0 or the rising edge of EN.

Figure 8-36 Open Load Detection Circuit

Figure 8-37 Off-State Open Load Detection Timing

Figure 8-38 Off-State Open Load Detection Timing