Protection- And Interface-Packing Load Switches Keep Close Tabs On Portables’s

Built around low-resistance, P-channel MOSFETs, the SmartSwitch line of load switches boasts of on-chip intelligent protection and interface functions, with the power managers expected to find wide use in cell phones, PDAs and other consumer electronics. The devices’s circuit protection features include fast current-limiting, over-temperature shutdown, short-circuit, and ESD protection. On the interface side, SmartSwtiches offer logic inputs, voltage-level shifting, fault-flag outputs, and ESD-protected inputs. The line is divided into external and internal load control categories. The former are current-limiting Smart-Switches that control external loads using either fixed or adjustable limits. They can provide port protection in USB or proprietary interfaces or for hot-plug applications involving PCMCIA cards and pc boards. The current-limiters are said to offer significant space savings and performance advantages over typical USB switches. For instance, instead of shutting down in an over-current mode, the devices go into a cycling mode that permits them to recover once a short-circuit is removed. Typical of the current-limiters is the AAT4618, a load switch that can operate over a 2.7V to 5.5V range and comes with a factory-programmed current limit of 500 mA or 1A. It also offers thermal overload protection. The devices come in SOT23, MSOP8, TSSOP8 and SOP8 packages. Internal load control devices feature a slow ramp-up of voltage to load and can be used to limit capactive in-rush current and prevent voltage spikes and sags on input supply rails. Called Softswitch SmartSwitches, the devices are used to protect power supplies, batteries and capacitors from current spikes. An under-voltage lockout capability turns the switch off when an input under-voltage condition exists. Two Softswitches are currently available: the AAT4250, a 120 m_ RDS(ON) (typ.), 1.8V to 5.5V input, and 1.5 ms turn-on and 10 µs turn-off time device; and the AAT4280, which offers flexible turn-on and turn-off characteristics, ranging from very fast to slew-rate limited. For more details, contact Jan Nilsson at ADVANCED ANALOGIC TECHNOLOGIES INC., Sunnyvale, CA. (408) 524-9684.