4 Distributed Architecture Using DC-DC Converter Module

Use of an integrated DC-DC transformer module can be the preferable choice for a distributed type of architecture. These integrated modules have an integrated transformer, which is switching at a very high frequency range of 11MHz to 15MHz. Using an integrated transformer module eliminates the need of external transformers, which results in a reduction in size and height of the overall system. An integrated transformer provides higher robustness to vibration. Additionally, these integrated DC-DC modules need only a few external discrete components; therefore, this architecture is simpler from the design and layout perspective.

TI offers several variants of the integrated DC-DC modules. These variants give the flexibility to choose the appropriate device, based on the availability of the input voltage rail in the system and required output voltage. Table 4-1 shows all variants and the technical specifications.

In a fully distributed architecture of the onboard charger, the architecture can be designed in different ways. The requirement of the pre-regulator to provide a regulated voltage rail to the integrated DC-DC modules depends on the power requirement for the gate drivers. As mentioned in Table 4-1, there is power derating in case of a wide input voltage range while connecting the integrated DC-DC module directly with the battery.

As Figure 4-1 shows, a separate integrated DC-DC module is used for each high-side gate driver and low-side gate drivers are supplied using flyback or push-pull devices using a multi-winding transformer. For the low side, it is possible to use same output winding of the transformer to supply bias power to multiple gate drivers that share the same ground.

Isolated bias power supply for the high side can be done using the bootstrap approach. As Figure 4-2 shows, isolated bias power for high-side gate drivers is generated using the bootstrap circuit. In the case of using a DC-DC module, each DC-DC module can be used to supply the low side directly and the high side using bootstrap. Other topologies like flyback, push-pull, and so forth, can be also be realized using the bootstrap approach. For a design with high switching frequency, especially in case of use of GaN switches, the power loss in the bootstrap diode can lead to thermal challenges. Therefore, the bootstrap approach can be more desireable in the case of low switching frequency designs.

Figure 4-3 shows a fully distributed architecture that can also be used for the isolated bias power supply to the gate drivers. Although this approach can be considered good from the safety point of view, simple design efforts, and so forth — due to the high number of devices, the cost is high for such architecture.