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LT3080-1 Datasheet(PDF) 9 Page - Linear Technology |
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LT3080-1 Datasheet(HTML) 9 Page - Linear Technology |
9 / 24 page LT3080-1 9 30801fc For more information www.linear.com/LT3080-1 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. TheLT3080-1canbeoperatedintwomodes.Threeterminal 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 300mV 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. Output Voltage The LT3080-1 generates a 10µA reference current that flows out of the SET pin. Connecting a resistor from SET to ground generates a voltage that becomes the reference point for the error amplifier (see Figure 1). The reference voltage is a straight multiplication of the SET pin current and the value of the resistor. Any voltage can be generated and there is no minimum output voltage for the regulator. A minimum load current of 1mA is required to maintain regulationregardlessofoutputvoltage.Fortruezerovoltage output operation, this 1mA load current must be returned to a negative supply voltage. With the low level current used to generate the reference voltage, leakage paths to or from the SET pin can create errors in the reference and output voltages. High quality insulationshouldbeused(e.g.,Teflon,Kel-F);cleaningofall insulatingsurfacestoremovefluxesandotherresidueswill probably be required. Surface coating may be necessary to provide a moisture barrier in high humidity environments. Board leakage can be minimized by encircling the SET pin and circuitry with a guard ring operated at a potential close to itself; the guard ring should be tied to the OUT pin. Guarding both sides of the circuit board is required. Bulk leakage reduction depends on the guard ring width. Ten nanoamperes of leakage into or out of the SET pin and associated circuitry creates a 0.1% error in the reference voltage. Leakages of this magnitude, coupled with other sources of leakage, can cause significant offset voltage and reference drift, especially over the possible operating temperature range. If guardring techniques are used, this bootstraps any stray capacitance at the SET pin. Since the SET pin is a high impedance node, unwanted signals may couple into the SET pin and cause erratic behavior. This will be most noticeable when operating with minimum output capacitorsatfullloadcurrent.Theeasiestwaytoremedy this is to bypass the SET pin with a small amount of ca- pacitance from SET to ground, 10pF to 20pF is sufficient. Stability and Output Capacitance The LT3080-1 requires an output capacitor for stability. It is designed to be stable with most low ESR capacitors (typically ceramic, tantalum or low ESR electrolytic). A minimum output capacitor of 2.2µF with an ESR of 0.5Ω or less is recommended to prevent oscillations. Larger values of output capacitance decrease peak deviations and provide improved transient response for larger load current changes. Bypass capacitors, used to decouple individualcomponentspoweredbytheLT3080-1,increase the effective output capacitor value. Forimprovementintransientperformance,placeacapaci- tor across the voltage setting resistor. Capacitors up to 1µF can be used. This bypass capacitor reduces system noise as well, but start-up time is proportional to the time constant of the voltage setting resistor (RSET in Figure 1) and SET pin bypass capacitor. Extra consideration must be given to the use of ceramic capacitors. Ceramic capacitors are manufactured with a variety of dielectrics, each with different behavior across Figure 1. Basic Adjustable Regulator + – LT3080-1 IN VCONTROL VCONTROL OUT 30801 F01 SET COUT RSET VOUT CSET + VIN + 25m applicaTions inFormaTion |
Similar Part No. - LT3080-1_15 |
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Similar Description - LT3080-1_15 |
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