Configure the circuit as shown in Figure 8-3. Connect (V+) to V_BAT which also powers the microcontroller. Resistors R₁ and R₂ create the under-voltage alert level of 2.0 V. When the battery voltage sags down to 2.0 V, the resistor divider voltage crosses V_REF, the 1.242 V reference threshold of the TLV3012-EP. This causes the comparator output to transition from a logic high to a logic low. The push-pull output of the TLV3012-EP is selected since the comparator operating voltage is shared with the microcontroller which is receiving the under-voltage alert signal.

Equation 1 is derived from the analysis of Figure 8-3.

Equation 1.

where

• R₁ and R₂ are the resistor values for the resistor divider connected to IN+
• V_BAT is the voltage source that is being monitored for an undervoltage condition.
• V_REF is the falling edge threshold where the comparator output changes state from high to low

Rearranging Equation 1 and solving for R₁ yields Equation 2.

Equation 2.

For the specific undervoltage detection of 2.0 V using the TLV3012-Q1, the following results are calculated.

Equation 3.

where:

• R₂ is set to 1 MΩ
• V_BAT is set to 2.0 V
• V_REF is set to1.242 V

Choose R_TOTAL (R₁ + R₂) such that the current through the divider is at least 100 times higher than the input bias current (I_BIAS). The resistors can have high values to minimize current consumption in the circuit without adding significant error to the resistive divider.