Datasheet LT3080-1 (Analog Devices) - 8

LT3080-1
block Diagram
IN VCONTROL 10µA + – 25mΩ 30801 BD SET OUT
applicaTions inFormaTion
The LT3080-1 regulator is easy to use and has all the pro- the positive input. Older adjustable regulators, such as the tection features expected in high performance regulators. LT1086 have a change in loop gain with output voltage Included are short-circuit protection and safe operating as well as bandwidth changes when the adjustment pin area protection, as well as thermal shutdown. is bypassed to ground. For the LT3080-1, the loop gain is The LT3080-1 is especially well suited to applications unchanged by changing the output voltage or bypassing. Output regulation is not fixed at a percentage of the output needing multiple rails. The new architecture adjusts down voltage but is a fixed fraction of millivolts. Use of a true to zero with a single resistor handling modern low volt- current source allows all the gain in the buffer amplifier age digital IC’s as well as allowing easy parallel operation to provide regulation and none of that gain is needed to and thermal management without heat sinks. Adjusting amplify up the reference to a higher output voltage. to “zero” output allows shutting off the powered circuitry and when the input is pre-regulated—such as a 5V or 3.3V The LT3080-1 also incorporates an internal ballast resistor input supply—external resistors can help spread the heat. to allow for direct paralleling of devices without the need for PC board trace resistors or sense resistors. This internal A precision “0” TC 10µA internal current source is con- ballast resistor allows multiple devices to be paralleled nected to the non-inverting input of a power operational directly on a surface mount board for higher output current amplifier. The power operational amplifier provides a low and higher power dissipation while keeping board layout impedance buffered output to the voltage on the non- simple and easy. It is not difficult to add more regulators inverting input. A single resistor from the non-inverting for higher output current; inputs of devices are all tied input to ground sets the output voltage and if this resistor together, outputs of all devices are tied directly together, is set to zero, zero output results. As can be seen, any and SET pins of all devices are tied directly together. Be- output voltage can be obtained from zero up to the maxi- cause of the internal ballast resistor, devices automatically mum defined by the input power supply. share the load and the power dissipation. What is not so obvious from this architecture are the ben- The LT3080-1 has the collector of the output transistor efits of using a true internal current source as the reference connected to a separate pin from the control input. Since as opposed to a bootstrapped reference in older regulators. the dropout on the collector (IN pin) is only 300mV, two A true current source allows the regulator to have gain supplies can be used to power the LT3080-1 to reduce and frequency response independent of the impedance on dissipation: a higher voltage supply for the control circuitry 30801fc 8 For more information www.linear.com/LT3080-1 Document Outline Features Applications Typical Application Description Absolute Maximum Ratings Pin Configuration Order Information Electrical Characteristics Typical Performance Characteristics Pin Functions Block Diagram Applications Information Typical Applications Package Description Revision History Typical Application Related Parts