Linear Technology announced the LT1618, constant current/constant voltage switching regulator which combines a traditional voltage feedback loop with a unique current feedback loop. This additional control loop may be used for either accurate input or output current resolution. The LT1618 is ideal for input current limited applications such as USB-powered devices, as well as current source applications like white LED drivers. With an input voltage range of 1.6V to 18V, the LT1618 can be powered by a variety of sources, ranging from two alkaline cells to several Li-Ion cells in a series. A current adjust pin allows control of input or output current over a 5 to 1 range.

The constant current design of this part makes it ideal for USB-powered applications but the voltage range also allows it to be used right up to power LED backlights at 12 to 15 V. The input range can actually be from 1.6 to 18 V while the output can be set up to 35 V. The operating switching frequency with the reference voltage of 1.263 V set on the feedback pin is a typical 1.4 MHz which allows for fairly small capacitors and inductor. When the output voltage is zero (feedback voltage at zero) the switching frequency falls to 550 kHz. The switch current limit is a typical 2.1 A -- with a switch saturation voltage of only about 200 mV at 1 A -- while the input current limit can be set to either 100 or 500 mA with a switch on the IADJ pin.