The TPS3703-Q1 0.7% maximum accuracy allows for adjustable voltage thresholds using external resistors without adding major inaccuracies to the device. In case that the desired monitored voltage is not available, external resistor dividers can be used to set the desired voltage thresholds. Figure 9-4 illustrates an example of how to adjust the voltage threshold with external resistor dividers. The resistors can be calculated depending on the desired voltage threshold and device part number. TI recommends using the 0.8V voltage threshold device such as the TPS3703B3080 because of the bypass mode of internal resistor ladder.

For example, consider a 2.0 V rail being monitored (V_MON) using the TPS3703B3080 variant. Using Equation 4, R1 = 15 kΩ given that R2 = 10 kΩ, V_MON = 2 V , and V_SENSE = 0.8 V. This device is typically meant to monitor a 0.8 V rail with ±3% voltage thresholds. This means that the device undervoltage threshold (V_IT-(UV)) and overvoltage threshold (V_IT-(OV)) is 0.776 V and 0.824 V respectively. Using Equation 4 , V_MON = 1.94 V when V_SENSE = V_IT-(UV). This can be denoted as V_MON-, the monitored undervoltage threshold where the device will assert a reset signal. Using Equation 4 again, the monitored overvoltage threshold (V_MON+) = 2.06 V when V_SENSE = V_IT+(OV). If a wider tolerance or UV only threshold is desired, use a device variant shown on Table 7 to determine what device part number matches your application.

There are inaccuracies that must be taken into consideration while adjusting voltage thresholds. Aside from the tolerance of the resistor divider, there is an internal resistance of the SENSE pin that may 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_SENSE) can be calculated by the sense voltage (V_SENSE) divided by the sense current (I_SENSE) as shown in Equation 6. V_SENSE can be calculated using Equation 4 depending on the resistor divider and monitored voltage. I_SENSE can be calculated using Equation 5.

Figure 9-4 Adjustable Voltage Threshold with External Resistor Dividers