Tiny 18-V eFuse power switch protects portable products

August 11, 2014 // By Graham Prophet
TI’s eFuse offers multiple levels of protection, extends battery life and reduces solution size in portable and adapter-powered devices.

Claimed as the smallest bidirectional 18-V, 5-A protection switches, with high power efficiency, TI intends these devices to be used in portable and adapter-powered devices, and enterprise and client solid state drives (SSDs).

TPS25940 and TPS25942 integrated circuits include back-to-back FETs to provide bidirectional current control, while reducing system size by 50% compared to discrete solutions. These smart eFuse ICs save board space by maintaining over/under voltage threshold accuracy of 2%, eliminating the need for a separate supply voltage supervisor chip.

The TPS25940 eFuse power switch integrates DevSleep mode, which enables hosts and devices to completely hibernate an SSD serial ATA (SATA) interface to reduce power consumption to less than 5 mW. The TPS25942 eFuse power multiplex (MUX) integrates an enable block function which allows the system to select between non-ideal diode mode and ideal diode mode.

In addition to DevSleep mode, these smart-eFuse devices integrate an active mode to reduce power consumption by providing an internal low-resistance switch (42 mΩ typical). Short-circuit response of 200 nsec minimises bus droop and supply stress during short-circuit events. An intelligent MUX function allows two supplies of equivalent voltage to be designated primary and secondary without turning off the overcurrent protection NFET of either, which reduces holdup capacitor requirements by up to 70%.

TI has also introduced a new power management unit (PMU) with six integrated buck regulators designed for the SandForce SF3700 SSD controllers for notebooks and PCs. The LM10692 provides phase-shifted operation at 2-MHz switching frequency to reduce the input-current ripple. The integrated PMU minimises inductor and capacitor size to save valuable board space. Using TI's LM10692 and MSP430 with SandForce’s SF3700 controller reduces system size to a 13.5 x 9.3-mm footprint.

The TPS25940 eFuse power switch, in a 20-pin, WQFN package is $0.85; TPS25942 eFuse power MUXin a 20-pin, WQFN package is $1.10; and the LM10692 PMU in a 36-pin, VQFN package is $2.80 (all 1000).

Texas Instruments; www.ti.com/tps25942-pr-eu /