The primary advantage of this application is being able to directly monitor a voltage on an automotive battery without needing external resistor dividers on the SENSEx inputs. This keeps the overall I_Q of the design low while still achieving the desired rail monitoring.

As shown in Figure 9-2, rail monitoring is done by connecting SENSE1 and SENSE2 inputs directly to the battery rail after the TVS protection diodes. The TPS38-Q1 that is being used in this example is a fixed voltage variant where SENSE1 and SENSE 2 threshold voltages have been set internally by the factory. Word of caution, the TVS protection diodes must be chosen such that the transient voltages on the monitored rails do not exceed the absolute max limit listed in Section 7.1.

To use this configuration, the specific voltage threshold variation of the device must be chosen according to the application. In this configuration, the '77' variation must be chosen for 7.7 V as shown in Table 10-1.

The device being able to handle 65 V on VDD means the monitored voltage rail can go as high as 42 V for the application transients and not violate the recommended maximum for the supervisor as it usually would. This is useful when monitoring a voltage rail that has a wide range that may go much higher than the nominal rail voltage such as in this case. Good design practice recommends using a 0.1 µF capacitor on the VDD pin and this capacitance may need to increase if using an adjustable version with a resistor divider.