The TPS73801 regulators incorporate several protection features that make them well suited for use in battery-powered circuits. In addition to the normal protection features associated with monolithic regulators, such as current limiting and thermal limiting, the device is protected against reverse input voltages, reverse output voltages, and reverse voltages from output to input.

Current limit protection and thermal overload protection are intended to protect the device against current overload conditions at the output of the device. For normal operation, the junction temperature must not exceed 125°C.

The input of the device withstands reverse voltages of 20 V. Current flow into the device is limited to less than 1 mA (typically less than 100 μA), and no negative voltage appears at the output. The device protects both itself and the load in such situations. This provides protection against batteries that can be plugged in backward.

The output of the TPS73801 can be pulled below ground without damaging the device. If the input is left open circuit or grounded, the output can be pulled below ground by 20 V. The output acts like an open circuit; no current flows out of the pin. If the input is powered by a voltage source, the output sources the short-circuit current of the device and protects itself by thermal limiting. In this case, grounding the EN pin turns off the device and stops the output from sourcing the short-circuit current.

The FB pin can be pulled above or below ground by as much as 7 V without damaging the device. If the input is left open circuit or grounded, the FB pin acts like an open circuit when pulled below ground and like a large resistor (typically 5 kΩ) in series with a diode when pulled above ground.

In situations where the FB pin is connected to a resistor divider that would pull the FB pin above its 7-V clamp voltage if the output is pulled high, the FB pin input current must be limited to less than 5 mA. For example, a resistor divider is used to provide a regulated 1.5-V output from the 1.21-V reference when the output is forced to 20 V. The top resistor of the resistor divider must be chosen to limit the current into the FB pin to less than 5 mA when the FB pin is at 7 V. The 13-V difference between OUT and FB pins divided by the 5-mA maximum current into the FB pin yields a minimum top resistor value of 2.6 kΩ.

In circuits where a backup battery is required, several different input/output conditions can occur. The output voltage can be held up while the input is either pulled to ground, pulled to some intermediate voltage, or is left open circuit. When the IN pin of the TPS73801 is forced below the OUT pin or the OUT pin is pulled above the IN pin, input current typically drops to less than 2 μA. This condition can happen if the input of the device is connected to a discharged (low voltage) battery and the output is held up by either a backup battery or a second regulator circuit. The state of the EN pin has no effect on the reverse output current when the output is pulled above the input.