STMicroelectronics` STBP120 protects the charging-control circuitry inside cellphones and other battery-powered portable equipment in case the external charger applies an excessive voltage. A number of variants are available, suitable for a range of charging-voltage levels including the USB voltages recommended by the current best-known proposals.

When implemented inside a battery-powered product, the STBP120 monitors the voltage from the connected charger. If the detected voltage exceeds a preset threshold, an internal solid-state switch is opened, thereby preventing the over-voltage from damaging the internal circuitry. There are four variants spanning threshold values from 5.375V to 6.02V, allowing engineers to optimize for USB chargers at up to 5.25V or other chargers at higher voltages up to 6.8V. Each device will protect against over-voltages as high as 28V.

In normal operation the internal switch, an N-channel MOSFET, has very low resistance of 90 milliOhms to promote efficiency and minimize heat dissipation. Other features include a fault-indicator output, soft-start capability to limit inrush current to the charging circuitry, and a thermal shutdown to protect against excessive temperature. The device can save pc-board space and component count in many other types of products where over-voltage protection is normally implemented using a discrete transient-voltage suppressor and a fuse. The over-voltage threshold can also be set more accurately than when using discrete devices.

The STBP120 is delivered in an ultra-small 2 x 2.5mm, 10-lead TDFN package, and is in full production priced at $0.37 in quantities of 1000 units.