Linear introduces surface-mount low-dropout regulator
By Paul Rako, Technical Editor -- EDN, July 23, 2007
The new LT3080 adjustable linear regulator from Linear Technology Corp has only a 1-mV offset between the voltage on the adjust pin and the output voltage, meaning that only 10 mΩ of PCB (printed-circuit-board)-trace resistance in the output path balances the currents among paralleled devices.
|
The device’s Set pin outputs a fixed 10-μA current that reacts against a resistor to create a fixed voltage. With only 10 mΩ trace resistance from your PCB that serves as emitter degeneration, the parts all share current. Maximum input voltage is 40V. The unit has separate pins for the NPN-pass-transistor collector and the power for the internal-chip circuitry, allowing the internal chip to operate from a higher voltage, so that you can drive the pass transistor to full saturation and provide a 300-mV dropout. If you can live with the normal dropout of a non-PNP part, you can also run the part with both pins wired together.
“This is the first change in architecture for linear regulators since the introduction of the three-terminal adjustable [regulator],” says Bob Dobkin, vice president of Linear and inventor of the new part. He points out that conventional linear regulators do not adjust the output to less than 1.2V. In contrast, the LT3080 adjusts down to 0V simply by using a low-value resistor. Another shortcoming of conventional regulators is that they are difficult to connect in parallel because a voltage sets the regulators, and the internal reference is not tightly controlled. You therefore must use significant ballasting resistors in the outputs of the paralleled devices to ensure that they share current. The LT3080 also has lower quiescent current than older linear regulators.
The LT3080 is available now and comes in eight-lead, 3×3-mm DFN packages, thermally enhanced MSOPs, five-lead TO-220 packages, and SOT-223 packages. Prices start at $1.81 (1000).
