As E-Bikes and other battery assisted vehicles are becoming increasingly popular in major cities, it is important to maintain electrical safety when designing with high-voltage, lithium-ion batteries. To safely operate such a battery, the discharge current rate and battery voltage level must be monitored. Undervoltage protection is crucial when using lithium-ion batteries because if the battery is discharged below its rated value, the battery will become damaged and potentially pose a safety hazard. In addition to undervoltage protection, it is important to ensure that the battery is discharging a safe current value. Combining undervoltage protection and overcurrent protection will ensure safe operation of the 48-V battery.

For this design, a 48-V, 20-Ah lithium-ion battery was selected. Monitoring a 48-V lithium ion battery can be achieved using the TLV9022 device in combination with the TL431 shunt reference. The TLV9022 is a dual-channel, open-drain comparator that will be used to implement overcurrent and undervoltage protection. This comparator was selected for its low-input offset voltage and fast response time. Additionally, this comparator has fault-tolerant inputs that can go up to 6V without damage. The design process will be broken down into three main sections: Voltage Regulation, Overcurrent Protection, and Undervoltage Protection with Hysteresis. This design has design parameters and desired outputs shown in the following table.

1. The design parameters and desired outputs table assumes a typical value of 29-V for the 48-V battery as it is the midpoint between the maximum voltage value and the undervoltage limit.
2. The design parameters and desired outputs table assumes only one condition (OC or UV) is met at a time at a time.

Since the intended use of the comparator outputs is to input them into a microcontroller, the desired reference voltage is approximately 3.3-V. The image below illustrates the circuit configuration for the TL431 device. Using the standard 1% resistor values shown, the voltage seen at the output of the TLV431 is 3.29-V. For the design process, see the TL431 / TL432 Precision Programmable Reference Data Sheet.

TL431 3.29-V Reference