3 Light Electric Vehicle System Overview

There are different types of LEVs: electric bikes (e-bikes), electric scooters (e-scooters), and electric motorcycles (e-motorcycles). E-bikes have the lowest power levels and shortest ranges with a more compact design. This is followed by e-scooters with a moderate range and power with a bigger design,then proceeded by e-motorcycles with the largest range and power, but with the bulkiest design.

An LEV system consists of multiple stages: DC/DC converter, the motor drive stage, the battery pack, and on-board or off-board charger. Non-isolated gate drivers are located in all stages when higher drive current is needed compared to an integrated motor driver. Non-isolated gate drivers can alternatively be considered when driving a FET when discrete implementation is preferred compared to a smart motor driver.

Figure 3-1 An Example Interleaved Boost PFC for an Off-Board Charger

For off-board charging, LEVs are seen paired with an external power conversion wall box or module. The power levels are higher for off-board chargers, sometimes exceeding over 1kW. An LEV fast charger takes an AC voltage from the grid (commonly from a garage wall charger or public charging rack/fast charger) and converts AC voltage into DC voltage within the charger to charge the batteries of the LEV. This voltage is regulated, maintained at a certain voltage, and power factor corrected to improve performance and efficiency. Non-isolated gate drivers such as the UCC27624 are used for high-efficiency driving. LEV battery chargers also occasionally use automotive grade parts instead of industrial grade. TI has a non-isolated gate driver portfolio that boasts many devices in both industrial and automotive grade.

On-board chargers (OBC) are more common in lower battery voltages and power levels. These OBCs typically have a PFC stage and DC/DC conversion stage built somewhere on the LEV. For more details, see Driving the Next xEV On-board Chargers and DC/DC Converters With High-Performing Non-isolated Gate Drivers.

Figure 3-2 Typical Battery Pack Topology

The battery pack of an LEV helps power the motors, sometimes with the help of a DC-DC converter. These battery packs must be able to produce high enough voltages to the motor when accelerating, but also not overheat during elongated use or high environmental temperatures. Additionally, batteries must have large capacity to have a larger range, but the weight of the batteries must be taken into consideration. Thus, efficient yet power-dense batteries are a must, and non-isolated gate drivers help achieve this. Using a dual-channel low-side driver like the UCC27624-Q1 to drive multiple FETs in a large battery. A small low-side driver like the UCC27517A-Q1 helps minimize short-circuit or overcurrent response time by quickly switching the battery discharge FET. To learn more, see the TI 16s Battery Pack Ref. Des. W/ Low-Side MOSFET Control for Large Capacity Apps reference design, which shows the UCC27524, but currently is pin-to-pin to the UCC27624, UCC27624V, UCC27624-Q1, and UCC27624V-Q1 shown in Figure 3-2 Additionally, see the E2E forum post: [FAQ] Which Battery Applications should I use Non-isolated Gate Drivers For?

Figure 3-3 Typical 96V to 12V DC-DC Converter Topology

Figure 3-4 Typical 48V to 12V DC-DC Topology

The DC-DC subsystem contains the high-voltage to low-voltage DC-DC conversion, typically stepping down that higher-voltage battery of 96V, 72V, or 48V down to 12V for lighting, horns, or other smaller electrical components. In this stage, high power density, reliability, and efficiency are key factors to what components are chosen. Another consideration is the voltage of the bootstrap supply pin on the high-side of a half-bridge gate driver, as this needs to provide ample headroom on the voltage – typically double of the battery voltage. Switching the FETs quickly in the appropriate battery level is critical for a gate driver, and TI’s UCC27834-Q1 has a 230V VHB for 96V and 72V systems and the UCC27301A-Q1 or LM2105 have a 120V VHB and 107V VHB respectively for a 48V battery system.

Figure 3-5 Typical Motor Drive Stage Topology

The motor driver stage of the LEV takes the electrical energy from the battery pack for the motor, which turns the wheels of the LEV. One of the most common topologies seen in an LEV is a BLDC motor. In this topology, gate drivers drive the two FETs that drive the phases a 3-phase brushless motor to either ground or the supply voltage. Using three half-bridge drivers such as the LM2105 or UCC27301A-Q1 can help minimize noise by allowing placement of the drivers as close to the FET as possible. Additionally, small packages such as the 2 × 2mm package of the LM2105 shrinks the PCB size, allowing for optimized designs. To learn more, see How to Choose a Gate Driver for DC Motor Drives.