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LT3080EQ-TR Datasheet(PDF) 8 Page - Linear Technology |
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LT3080EQ-TR Datasheet(HTML) 8 Page - Linear Technology |
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8 / 26 page  LT3080 8 3080fb The LT3080 regulator is easy to use and has all the pro- tection 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 con- nected to the noninverting input of a power operational amplifier. The power operational amplifier provides a low impedance buffered output to the voltage on the noninvert- ing 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 ben- efits 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 dis- sipation: 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 the collector 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. – + VCONTROL IN 10μA 3080 BD OUT SET BLOCK DIAGRAM APPLICATIONS INFORMATION |
Similar Part No. - LT3080EQ-TR |
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Similar Description - LT3080EQ-TR |
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