The switch is easily controllable by using an output of the MCU to toggle a control pin. The input-voltage switch is an integrated transistor that connects the battery voltage to a separate pin. With its ultra-low quiescent current and integrated V IN switch, the TPS62746 buck converter is a good fit for such applications. This results in lower average power consumption of the MCU and increases the battery’s operating runtime. In battery-powered applications where you need the longest lifetime, you must also step down the battery voltage to an appropriate level to supply the MCU. With this configuration, an output of the MCU controls the switch.įigure 2 shows the basic block diagram of such a discrete implementation consisting of a switch, resistor divider and low-power MCU with integrated ADC.įigure 2: Adding a level shifter to reduce the current A p-channel is typically the switch, with an n-channel MOSFET used as the level shift to drive the p-channel.
To avoid these additional losses due to the current through the resistor divider, you can use a switch to connect the resistor divider and the ADC input to the battery only when you need a measurement. This is about the same as the operating current of a MCU in low-power mode and can therefore have a strong reduction on your battery runtime. The current through the resistor divider will be in the range of 2♚. With a battery voltage of 4.2V and resistor values of 1.5MΩ and 470kΩ, the maximum ADC input voltage is 1V. Figure 1 shows a simple implementation.įigure 1: A resistor divider scales down the battery voltage to the ADC input range Scaling down the battery voltage to match the ADC input range requires an external resistor divider. The easiest way to get the status of the battery is to feed the battery voltage into an analog-to-digital converter (ADC) and process the data. With this information, the system MCU can estimate the runtime and signal when the battery needs replacing or recharging. A common requirement in battery-powered applications like metering, handheld or wearable products is to know the charge level of the battery.
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