blocking (RCB). In the case of USB Type-C AC adapters, it’s also necessary to support fast role swapping (FRS) that complies with the timing requirement defined in the USB Power Delivery specification. It’s possible to design protective circuits to implement all these functions, but the design process takes time. Also, obtaining UL or IEC 62368-1 safety recognition can further extend time to market. In addition, a solution using discrete components can increase overall solution footprint. To quickly implement compact and accurate protection functions that meet UL and IEC safety standards, designers can turn to eFuse regulators. These integrated protection ICs have programmable protection thresholds to support
design flexibility, and protection can be latching or have automatic recovery when the fault is removed. They have low “on” resistance to maximize efficiency and include soft start to minimize inrush currents. Some models include certified FRS capability for use in USB Type-C AC adapters. This article provides an introduction to eFuses, including voltage and current ratings and representative applications. It then looks at how protection functions including, OCP, soft start, OVP, UVLO, and OTP are implemented. It closes by presenting a series of eFuse ICs from Littelfuse optimized for specific applications, along with system integration considerations to speed time to market.
eFuse selection criteria eFuse requirements for a given application are strongly related to the operating voltage and current of the system. For low voltage and low current systems up to about 5 volts direct current (V DC ) input and 2 amperes (A) of current, features such as OCP, OTP, UVLO, and inrush current suppression (dV/dt) for hot-swap and hot-plug events are commonly required. For applications that consume between 2 and 6 A, with input voltages up to 24 V DC , OVP, current limiting/OCP, and “power good” signals are often needed. Current timers and monitors for system monitoring and OCP and RCB, are common in applications using 6 A and higher and voltages of 24 V DC and higher (Figure 1).
Ensuring compact, flexible, and accurate circuit protection that meets IEC and UL safety standards
Device and end-user protection against potentially damaging voltage, current, and temperature conditions are needed in applications like USB Type-C® alternating current (AC) adapters, networking equipment, and consumer and industrial electronics. Using conventional fuses or positive temperature coefficient thermistors (PTCs) can provide compact
solutions and some protection. However, a growing number of applications require higher levels of protection and greater flexibility, including faster response times and programmable and resettable overvoltage protection (OVP), overcurrent protection (OCP), undervoltage lockout (UVLO), overtemperature protection (OTP), soft start, and/or reverse-current
By Jeff Shepard Contributed By DigiKey's North American Editors
Figure 1: eFuse feature sets are strongly correlated with the input voltage (horizontal axis) and input current (vertical axis) of the application. (Image source: Littelfuse)
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