1 Introduction

The transition of vehicle architectures from domain- to zone-based is significantly changing automotive power distribution, with semiconductor switch-based solutions (see Figure 1) replacing the traditional melting fuses used for wire harness protection. These solutions offer benefits such as less variability in fuse-time currents, which can then potentially reduce the cable diameter, weight and cost of the wire harness. Semiconductor switches are also resettable remotely, which means that the fuses do not have to be easily accessible, giving designers the ability to place the fuses in locations that can reduce cable lengths from the power source to the load.

The system design challenges when using semiconductor switches as smart fuse devices include lowering the quiescent current when the switch is in the on state, as well as turning on outputs powering large capacitive loads typically seen at the load (the electronic control unit [ECU] input). ECUs have an input capacitance ranging from 47µF to 5mF and startup time considerations (fast charging time <1ms, medium charging time <10ms, slow charging time <50ms) based on the ECU type and number of ECUs connected together on each Power Distribution Box (PDB) output. Charging these ECU input capacitors through the metal-oxide semiconductor field-effect transistor (MOSFET) switch within the ECU startup time is one of the primary system design challenges of a zone-based architecture.

In this article, we’ll discuss various techniques to address the challenge of driving capacitive loads using high-side switch controllers.