The TPS798-Q1 incorporates several protection features that make the device designed 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, and reverse currents 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. The junction temperature must not exceed 125°C.

The input of the device withstands reverse voltages of –60V. Current flow into the device is limited to less than 6mA (typically, less than 100μA), and no negative voltage appears at the output. The TPS798-Q1 protects both the device and the load. This architecture also provides protection against batteries that can be plugged in backwards.

The FB pin of the adjustable device can be pulled above or below ground by as much as 7V without damaging the device. If the input is left open or grounded, the FB pin behaves as an open circuit when pulled below ground, or as a large resistor (typically, 100kΩ) in series with a diode when pulled above ground. If the input is powered by a voltage source, pulling the FB pin below the reference voltage increases the output voltage. This configuration causes the output to go to a unregulated high voltage. Pulling the FB pin above the reference voltage turns off all output current.

In situations where the FB pin is connected to a resistor divider that pulls the FB pin above the 7V clamp voltage if the output is pulled high, the FB pin input current must be limited to less than 5mA. For example, a resistor divider provides a regulated 1.5V output from the 1.275V reference when the output is forced to 28V. The top resistor of the resistor divider must be chosen to limit the current into the FB pin to less than 5mA when the FB pin is at 7V. The 21V difference between the OUT and FB pins divided by the 5mA maximum current into the FB pin yields a minimum top resistor value of 5.8kΩ.

In circuits where a backup battery is required, several different input and 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. The rise in reverse output current above 7V occurs from the breakdown of the 7V clamp on the FB pin. With a resistor divider on the regulator output, this current is reduced, depending on the size of the resistor divider.

When the IN pin of the TPS798-Q1 is forced below the OUT pin, or the OUT pin is pulled above the IN pin, input current typically drops to less than 0.6mA. This scenario can occur if the input of the TPS798-Q1 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.