When driving off-board loads, an open-load fault can result from a wire break, a gap in the solder or any other physical disconnection in the conduction path between the switch and the load (or the load and ground). To pass system reliability tests, these failures must occur at very low rates. Despite this, it is common for the high-side switches to detect open-loads when they occur. A short to battery is a fault that occurs when the input of the switch and the output of the switch are shorted together. Open load and short-to-battery faults exhibit the same signature when the fault occurs, so the detection and reporting mechanisms are the same.

To detect an open-load or short to battery in the off state, a weak drain-to-source pullup is activated and the drain-to-source voltage is measured. If this difference is less than the open-load detection threshold for the device, then it is effectively the same and the device determines that the output is not discharging to ground. Therefore, either the terminals of the switch are shorted, as in a short-to-battery fault, or there is some break in the conduction path. The FLT pin then goes low and the SNS reports this with a logic high.

To detect these faults in the on-state, some additional intelligence is required. These faults occur when the switch is on, but little to no current flows through it. To detect this, an MCU compares the low, ADC-reported sense current against the current levels expected during normal conditions. Then by cross-checking that the EN signal is high, the MCU can know that there is an open load or short to battery.

With integrated ADCs and pull-up networks, SPI-controlled high-side switches and smart eFuse high-side switches have the ability to detect these faults in the on and off states and differentiate between them.