摘要
In 48V electric vehicle (EV) power systems, high-side battery switching requires an advanced load switch (LS) capable of bidirectional current flow and reverse current blocking for efficient and safe power management. During the battery charging phase, a single charger sequentially charges multiple battery cells (Fig. 32.6.1 top left). The LS that is connected between the charger and the battery cells must block reverse current in the off state to prevent the charged battery from discharging. Moreover, during the battery discharge phase, the LS enables current to flow from the battery to the load. Therefore, the LS requires bidirectional current transfer to charge the battery cells and power the load. The conventional LS [1]–[6] adopts one power switch (PS) to transfer current from the first to the second terminal. However, the current may flow from the second terminal to the first terminal through the body diode, even if the PS is off. To block the reverse current, LSs with back-to-back (B2B) PSs are proposed in [7]–[9]. Although the body diodes in opposite directions block the reverse current, these LSs do not provide a bidirectional current transfer path since their gate drivers (GD) are only functional when the voltage of a specified terminal is higher. In recent years, the bidirectional LS (BLS) proposed in [10]–[12] can block reverse current and transfer current bidirectionally. However, the B2B PS inevitably doubles the on-resistance $(\mathrm{R}_{\text{on}})$, significantly increasing the conduction loss. To minimize loss, Gallium Nitride $(\text{GaN})$ devices are particularly well-suited for PS use due to their low $\mathrm{R}_{\text{on}}$. The cutting-edge technology of monolithic bidirectional GaN (Bi-GaN) [13], [14] further reduces the $\mathrm{R}_{\text{or}}$ compared to discrete B2B GaN PSs (Fig. 32.6.1 middle left). Bi-GaN acts similarly to B2B GaN but with a smaller $\mathrm{R}_{0\Gamma}$ due to common drain/source (CD/CS) terminals. The first mode $(\mathrm{V}_{\text{GlS}1}=\mathrm{V}_{\mathrm{G}2\mathrm{S}2}=0\mathrm{V}]$ and the second $(\mathrm{V}_{\text{GlS}1}=\mathrm{V}_{\mathrm{G}2\mathrm{S}2}=5\mathrm{V})$ exhibit bidirectional current blocking and transfer, respectively. In short, Bi-GaN is an excellent choice for BLS. The bottom of Fig. 32.6.1 shows the structures of 100V monolithic Bi-GaN with CS (MBS) and monolithic Bi-GaN with CD (MBD), where the length from gate to drain $(\mathrm{L}_{\text{gd}})$ is about three times the length of the gate to source $(\mathrm{L}_{\text{gs}})$. Compared to discrete B2B topologies, the size of MBS is reduced by 13%, while MBD is significantly reduced by 38%, lowering area and $\mathrm{R}_{\text{on}}$ since $\mathrm{R}_{\text{on}}$ has a positive relationship with $\mathrm{L}_{\mathrm{g}}$. and $\mathrm{L}_{\text{gc}}$. Besides, although the CS topology allows two gates to be driven by the same GD so that the two gates can be merged into one [13], [14], overstress occurs during the turn-off process since the source terminal is not available to bias (Fig. 32.6.1 top right). When the input control signal $(\mathrm{V}_{\text{PWM}})$ goes from high to low, GD pulls the gate voltage $(\mathrm{V}_{\mathrm{G}})$ down to the ground. The charge on the source terminal is gradually discharged by $\mathrm{R}_{\text{Load}}$, leading to a large drop in the gate-to-source voltage $(\mathrm{V}_{\text{GS}})$ that may exceed the gate-to-source breakdown voltage. Thus, an additional turn-off selector is required to control the gate terminal to short to the lower voltage of either the first terminal $(\mathrm{V}_{\mathrm{D}1})$ or the second terminal $(\mathrm{V}_{\mathrm{D}2})$. The turn-off selector solves the overstress problem at the cost of complex control design. Based on the characteristics of the Bi-GaN devices and the consideration of the GD design, this work adopts MBD as the main PS to implement the BLS for low cost, high efficiency, and more straightforward GD design.