Information in the following applications sections is not part of the TI component specification, and TI does not warrant its accuracy or completeness. TI’s customers are responsible for determining suitability of components for their purposes. Customers should validate and test their design implementation to confirm system functionality.
The TLV349x family of comparators features rail-to-rail input and output on supply voltages as low as 1.8 V. The push-pull output stage is optimal for reduced power budget applications and features no shoot-through current. Low supply voltages, common-mode input range beyond supply rails, and a typical supply current of 0.8 µA make the TLV349x family an excellent candidate for battery-powered applications with single-cell operation.
One of the benefits of AC coupling a single-supply comparator circuit is that it can block dc offsets induced by ground-loop offsets that could potentially produce either a false trip or a common-mode input violation. Figure 18 shows the TLV3491 configured as an AC-coupled comparator.
Design requirements include:
The TLV349x can be configured as a relaxation oscillator to provide a simple and inexpensive clock output, as Figure 20 shows. The capacitor is charged at a rate of 0.69 RC. It also discharges at a rate of 0.69RC. Therefore, the period is 1.38 RC. R1 may be a different value than R2.
The reset circuit shown in Figure 21 provides a time-delayed release of reset to the MSP430 microcontroller. Operation of the circuit is based on a stabilization time constant of the supply voltage, rather than on a predetermined voltage value. The negative input is a reference voltage created by a simple resistor divider.
These resistor values must be relatively high to reduce the current consumption of the circuit. The positive input is an RC circuit that provides a power-up delay. When power is applied, the output of the comparator is low, holding the processor in the reset condition. Only after allowing time for the supply voltage to stabilize does the positive input of the comparator become higher than the negative input, resulting in a high output state and releasing the processor for operation. The stabilization time required for the supply voltage is adjustable by the selection of the RC component values.
Use of a lower-valued resistor in this portion of the circuit does not increase current consumption because no current flows through the RC circuit after the supply has stabilized. The required reset delay time depends on the power-up characteristics of the system power supply. R1 and C1 are selected to allow enough time for the power supply to stabilize. D1 provides rapid reset if power is lost. In this example, the R1 × C1 time constant is 10 ms.