The TPS3704-Q1 maximum accuracy (1%) allows for adjustable voltage thresholds using external resistors without adding major inaccuracies to the device. In case the desired monitored voltage is not available, external resistor dividers can be used to set the desired voltage thresholds. Figure 8-2 illustrates an example of how to adjust the voltage threshold with external resistor dividers. For assistance in calulating the external resistors access the TPS3704 adjustable threshold voltage resistor calculator in the Design Tools and Simulation section of the TPS3704 product page. The resistors can be calculated depending on the desired voltage threshold and device part number. TI recommends using a voltage threshold device variant because of the bypass mode of the internal resistor ladder.

For example, consider a 2.0-V rail being monitored (V_MON) using the TPS37042BJOFDDFRQ1 variant. Using Equation 2, R1 = 15 kΩ given that R2 = 10 kΩ, V_MON = 2 V, and V_SENSE1 = 0.8 V. This device is typically meant to monitor a
0.8-V rail with ±4% voltage thresholds. This means that the device undervoltage threshold (V_IT-(UV)) and overvoltage threshold (V_IT+(OV)) is 0.768 V and 0.832 V, respectively. Using Equation 2, V_MON = 1.92 V when V_SENSE1 = V_IT-(UV). This can be denoted as V_MON-, the monitored undervoltage threshold where the device asserts a reset signal. Using Equation 2 again, the monitored overvoltage threshold (V_MON+) = 2.08 V when V_SENSE1 = V_IT+(OV). If a wider tolerance or UV only threshold is desired, use a device variant listed in
Table 9-3 to determine which device part number matches which application.

There are inaccuracies that must be taken into consideration when adjusting voltage thresholds. Aside from the tolerance of the resistor divider, there is an internal resistance of the SENSE1 pin that can affect the accuracy of the resistor divider. Although expected to be very high impedance, users are recommended to calculate the values for design specifications. The internal sense resistance R_SENSE1 can be calculated by the sense voltage V_SENSE1 divided by the sense current I_SENSE1 as shown in Equation 4. V_SENSE1 can be calculated using
Equation 2 depending on the resistor divider and monitored voltage. I_SENSE1 can be calculated using Equation 3.

Figure 8-2 Adjustable Voltage Threshold With External Resistor Dividers