Adding Hysteresis to Low-Battery Input on the TPS6211x

The low-battery input (LBI), available on several step-down converters, is often used to shut down the converter when the input voltage falls below a set threshold. This prevents damage to the battery and signals that the battery is at the end of its life and must be charged or replaced. Batteries have internal resistance that causes the voltage to drop as the load increases. This internal resistance introduces a challenge when monitoring the battery level. When the converter shuts off and current draw drops to zero, the reduced current flow through the internal resistance of the battery causes the battery’s terminal voltage to increase. In many cases, the voltage increases above the LBI threshold, which causes the device to turn on and begin drawing current. This then leads to a drop across the internal resistance that trips the LBI threshold again and turns off the device, and the process repeats. This adds an unwanted oscillation to the output as the converter turns on and off. Adding hysteresis to the low-battery input eliminates this oscillatory behavior. This application report describes how to add hysteresis to the LBI circuitry for the TPS62113 converter.