While the switch is disabled and DIA_EN high, an internal comparator watches the condition of V_OUT. The TPS272C45 includes a nominally 150-kΩ pull-up resistor from OUT pin to VS pin in series with a switch controlled by the DIA_EN signal. So, if the load is disconnected (open load condition) or there is a short to supply the V_OUT voltage is pulled towards V_VS. In either of these events, the internal comparator measures V_OUT as higher than the open load threshold (V_OL,off) and a fault is indicated on the FLT pin (Version A) or FLTx pins (Version D) and on the SNS pin (only for versions A, B, C). No external component is required in most cases, however if there is a pull-down resistor to GND on V_OUT, an additional external pull-up resistor can be necessary to bias V_OUT appropriately.

Open load fault signaling on the SNS and the internal pull-up on OUT is enabled only if DIA_EN is set HI. To detect open-load threshold at higher pull-down load current, an external pull-up resistor (and potentially a switch) can be needed.

While the switch is disabled, the fault indication mechanisms continuously represent the present status. For example, if V_OUT decreases from greater than V_{OL_off} to less than V_{OL_off}, the fault indication is reset. Additionally, the fault indication is reset upon the falling edge of DIA_EN (for SNS pin) or the rising edge of EN.

Figure 9-17 Open-Load Detection Circuit

Figure 9-18 Open-Load Detection Timing