Ensuring compact, flexible, and accurate circuit protection that meets IEC and UL safety standards
( Figure 6 ). The 50 milliohm (mΩ) on resistance of the internal switch minimizes power dissipation. The OVP reacts immediately in the event of excessive voltage and discharges the output capacitor. The current limit threshold is set with an external resistor, and the OCP operates in hiccup mode for overcurrent or short-circuit conditions. The automatic soft start function provides a smooth voltage ramp up, limiting the inrush current to a safe level.
time, programmable current limit threshold up to 5 A, short-circuit protection, UVLO, and fold-back OTP. Two models are available: The LS1205EV includes three selectable input voltage ranges. The output clamp voltage and UVLO thresholds are based on the selected input voltage range. The LS1205EF includes an open drain fault indicator function that signals the occurrence of UVLO, OVP, short-circuit, and thermal shutdown faults. 28-volt eFuse with RCB and FRS Designers of notebooks and tablet computers, docking stations, and network devices that need Thunderbolt or USB Type-C PD functionality with RCB and FRS, can turn to the LS2406ERQ23 28 volt, 6 A eFuse regulator that includes OCP, OVP, short-circuit, soft start and OTP ( Figure 7 ). The power switch has an on resistance of 24 mΩ to minimize power dissipation during normal operation, the OCP, OVP and soft start functions are programmable, and the OTP includes automatic recovery when the device cools. This eFuse features an always-on RCB function regardless of the enable signal (EN) logic state. FRS and the integrated input and output discharge functions meet the USB PD specifications.
18 volt / 5 A eFuses The LS1205E series eFuses have an operating voltage range of 2.7 to 18 VDC, a current rating of 5 A, and are suitable for use in hard disk drives, solid-state disk drives, and adapter-powered devices like notebook computers and networking devices. These eFuses feature a switch with a 25 mΩ on resistance and are in a 10-lead DFN3×3 package. They include programmable soft start
• High-amperage power traces should be sized to carry at least twice the maximum expected current and should be as short as possible. • The GND terminal of the eFuse must be connected directly to the pc board ground plane. The ground plane of the pc board should be an island or copper plane. For the LS1205E series only: Locate all support components like RILIM, capacitor SS (CSS), and resistors for EN, as close as possible to the corresponding connection pin, and use the shortest possible trace length to connect the other side of the component to GND. The traces should be placed to prevent coupling to any switching signals on the pc board, and the length of the traces for the RILIM and CSS components should be as short as possible to minimize the effect of parasitics on the current limit setting and soft start timing.
For the LS2406ERQ23, refer to the datasheet for layout considerations related to USB Type-C cable short-circuit protection and FRS components. Conclusion For protection of both users and devices, and to meet applicable standards, designers can turn to integrated protection eFuse regulators that provide a variety of functions including OVP, OCP, ULVO, OTP, and reverse-current blocking. With programmable protection thresholds and reset capability, eFuses support design flexibility, while also featuring low “on” resistance switches to maximize efficiency and include soft start to minimize inrush currents. Some models include certified FRS and RCB for use in USB Type-C AC adapters.
The LS2406ERQ23 comes in a low- profile, 16-lead QFN 2.5 millimeter (mm) x 3.2 mm package and is UL Recognized to UL/CSA 62368-1. Board layout guidelines For the LS1205E series, as well as the LS0505EVD22 and LS0504EVT233, here are some general board layout considerations to help ensure a successful implementation: • A 0.1 microfarad (µF) or larger ceramic decoupling capacitor should be placed between the IN terminal and ground (GND), and between the OUT terminal and GND. When the input power path inductance is negligible, such as in hot-plug applications, this capacitor may not be necessary. • Decoupling capacitors should be placed as close as possible to the IN, OUT, and GND terminals, and the loop area formed by the connections must be minimized.
Figure 6: The LS0504EVT233 eFuse is in a compact SOT23 package for use in space-constrained applications. (Image source: Littelfuse)
Figure 7: Typical application of the LS2406ERQ23 eFuse supporting reverse-current blocking and FRS for USB Type-C PD applications. (Image source: Littelfuse)
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