BESCHREIBUNG

The LT3080 is a 1.1A low dropout linear regulator that can be paralleled to increase output current or spread heat in surface mounted boards. Architected as a precision current source and voltage follower allows this new regulator to be used in many applications requiring high current, adjustability to zero, and no heat sink. Also the device brings out the collector of the pass transistor to allow low dropout operation —down to 350 millivolts— when used with multiple supplies.A key feature of the LT3080 is the capability to supply a wide output voltage range. By using a reference current through a single resistor, the output voltage is programmed to any level between zero and 36V. The LT3080 is stable with 2.2µF of capacitance on the output, andthe IC uses small ceramic capacitors that do not require additional ESR as is common with other regulators. Internal protection circuitry includes current limiting and thermal limiting. The LT3080 regulator is offered in the 8-lead MSOP (with an exposed pad for better thermal characteristics), a 3mm × 3mm DFN, 5-lead DD-Pak,  TO-220 and a simple-to-use 3-lead SOT-223 version.

 

FEATURES

Outputs May Be Paralleled for Higher Current and Heat Spreading

Output Current: 1.1A

Single Resistor Programs Output Voltage

1% Initial Accuracy of SET Pin Current

Output Adjustable to 0V

Low Output Noise: 40µVRMS (10Hz to 100kHz)

Wide Input Voltage Range: 1.2V to 36V

Low Dropout Voltage: 350mV (Except SOT-223 Package)

<1mV Load Regulation

<0.001%/V Line Regulation

Minimum Load Current: 0.5mA

Stable with 2.2µF Minimum Ceramic Output Capacitor

Current Limit with Foldback and Overtemperature Protected

Available in 8-Lead MSOP, 3mm × 3mm DFN,

5-Lead DD-Pak, TO-220 and 3-Lead SOT-223

AEC-Q100 qualifiziert für Automobilanwendungen

 

ANWENDUNGEN

High Current All Surface Mount Supply

High Efficiency Linear Regulator

Post Regulator for Switching Supplies

Low Parts Count Variable Voltage Supply

Low Output Voltage Power Supplies

 

ANWENDUNGSINFORMATIONEN

The LT3080 regulator is easy to use and has all the protection features expected in high performance regulators. Included are short-circuit protection and safe operating area protection, as well as thermal shutdown.The LT3080 is especially well suited to applications needing multiple rails. The new architecture adjusts down to zero with a single resistor handling modern low voltage digital IC’s as well as allowing easy parallel operation and thermal management without heat sinks. Adjusting to “zero” output allows shutting off the powered circuitry and when the input is pre-regulated—such as a 5V or 3.3V input supply —external resistors can help spread the heat.A precision “0” TC 10µA internal current source is connected to the noninverting input of a power operational amplifier. The power operational amplifier provides a low impedance buffered output to the voltage on the noninverting input. A single resistor from the noninverting input to ground sets the output voltage and if this resistor is set to zero, zero output results. As can be seen, any output voltage can be obtained from zero up to the maximum defined by the input power supply.What is not so obvious from this architecture are the benefits of using a true internal current source as the reference as opposed to a bootstrapped reference in older regulators. A true current source allows the regulator to have gain and frequency response independent of the impedance on the positive input. Older adjustable regulators, such as the LT1086 have a change in loop gain with output voltage as well as bandwidth changes when the adjustment pin is bypassed to ground. For the LT3080, the loop gain is unchanged by changing the output voltage or bypassing. Output regulation is not fixed at a percentage of the output voltage but is a fixed fraction of millivolts. Use of a true current source allows all the gain in the buffer amplifier to provide regulation and none of that gain is needed to amplify up the reference to a higher output voltage.The LT3080 has the collector of the output transistor connected to a separate pin from the control input. Since the dropout on the collector (IN pin) is only 350mV, two supplies can be used to power the LT3080 to reduce dissipation: a higher voltage supply for the control circuitry and a lower voltage supply for the collector. This increases efficiency and reduces dissipation. To further spread the heat, a resistor can be inserted in series with thecollector to move some of the heat out of the IC and spread it on

the PC board.The LT3080 can be operated in two modes. Three-terminal mode has the control pin connected to the power input pin which gives a limitation of 1.35V dropout. Alternatively, the “control” pin can be tied to a higher voltage and the power IN pin to a lower voltage giving 350mV dropout on the IN pin and minimizing the power dissipation. This allows for a 1.1A supply regulating from 2.5VIN to 1.8VOUT or 1.8VIN to 1.2VOUT with low dissipation.