Simple power indicator undervoltage/overvoltage detection

Summary: Undervoltage/overvoltage (UV/OV) indicators, also called power-good (THIN) indicators, can notify portable device users when the battery voltage is too low or the battery is overcharged. Bo indicators typically control an external FET that blocks the supply voltage during such faults. They are also useful as simple indicators where there is no FET shown.

The Power Good (THIN) LED indicates when the power supply is within the specified range. Also known as an Under Voltage/Over Voltage (UV/OV) indicator, this indicator notifies the user of a portable device when the battery voltage is too low or the battery is overcharged.

Although it is not difficult to design a circuit for this purpose using logic gates, two comparators, three bypass capacitors, an LED, and five resistors, the circuit of Figure 1 saves board space while reducing the cost of the circuit.

Figure 1. Housed in a 1.0 mm x 1.5 mm μDFN package, this IC illuminates an LED as long as the power supply is OK. When an under- or overvoltage condition occurs, it turns off the LED and issues a warning to the microcontroller.

The MAX4923-MAX4926 series of overvoltage protectors are typically connected to the power supply through an external P-channel FET and the load, which is usually as long as the power supply is determined. The factory preset voltage thresholds of these devices are listed in Table 1.

These chips, however, can also be used as simple power-good indicators. Use the following formula to calculate Figure 1

, where (for example) ≤10mA, typical at 25°C through 160Ω, and VIN is the applied source voltage.