Advanced Analogic Technologies Introduces Lowest-Power Load Switch Available for Biometric Security Devices

Packaged in a compact 8-pin, 2x2-mm FTDFN package, the AAT4702 is a current-limited P-channel metal–oxide–semiconductor field-effect transistor (MOSFET) power switch with an integrated LDO regulator that offers a variety of protection features including auto restart, reverse current blocking and a fault flag to deliver the highest available level of load current protection in a load switch.

“A growing number of applications, such as fingerprint sensing circuits, require both a system power supply and load current protection. The AAT4702 does both,” said CJ Zhang, product line vice president. “By integrating a current limited load switch and an LDO in a single compact IC that requires minimal power resources, our new load switch gives notebook and mobile device designers an opportunity to support these applications in a much smaller, lower power circuit.”

A member of AnalogicTech’s Application Specific Power MOSFET (ASPM) product family, the AAT4702’s load switch current limit is set at 150 mA as a default, but it is programmable up to 1A via an external set resistor. To further protect system loads or peripheral circuits from over-current conditions, the new load switch adds an auto-restart function that wakes up and re-enables the device every 40 ms to check for the continued existence of an over-current condition. If the over-current condition remains, the AAT4702 stays in shutdown mode with both the load switch and LDO regulator output pulled low to ground. This allows the device to automatically resume operation once the over-current condition ends, eliminating the risk of damage.

An integrated FAULT flag feature that indicates an over-current or over-temperature condition is also available, adding a 5 ms blanking time to prevent reports of false events. The AAT4702 also adds reverse current blocking to protect the load switch from reverse current potentials when the device is shut down. The integrated load switch/LDO operates from inputs ranging from 2.4V to 5.5V.

The LDO integrated into the AAT4702 delivers a regulated 1.8V supply voltage with plus or minus 2 percent accuracy at load levels up to 100 mA. It may be powered either directly from an input source supply or via the load switch output. Quiescent current for the AAT4702 is 15 micro A typical, by far the lowest specification in the industry for integrated solutions of this type. Shutdown current is less than 1 micro A. The single-chip solution offers up to a 50 percent board space savings compared to comparable discrete solutions.