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TPS73430DRBT Datasheet(PDF) 8 Page - Texas Instruments |
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TPS73430DRBT Datasheet(HTML) 8 Page - Texas Instruments |
8 / 20 page APPLICATION INFORMATION Input and Output Capacitor Requirements Feedback Capacitor Requirements GND EN NR IN OUT TPS734xx Optionalbypasscapacitor toreduceoutputnoise andincreasePSRR. Optionalinputcapacitor. Mayimprovesource impedance,noise,orPSRR. V IN V EN 2.2 F Ceramic m V OUT Output Noise GND EN FB IN OUT Optionalinputcapacitor. Mayimprovesource impedance,noise,orPSRR. TPS73401 2.2 F Ceramic m V IN V EN R 1 R 2 C FB V OUT (R +R ) 1 2 R 2 V OUT = ´ 1.208 TPS734xx SBVS089F – DECEMBER 2007 – REVISED FEBRUARY 2009 ........................................................................................................................................ www.ti.com The TPS734xx family of LDO regulators combines the high performance required of many RF and Although an input capacitor is not required for precision analog applications with ultra-low current stability, it is good analog design practice to connect consumption. High PSRR is provided by a high gain, a 0.1 µF to 1µF low equivalent series resistance high bandwidth error loop with good supply rejection (ESR) capacitor across the input supply near the at very low headroom (VIN – VOUT). Fixed voltage regulator. The ground of this capacitor should be versions provide a noise reduction pin to bypass connected as close as the ground of output capacitor; noise generated by the bandgap reference and to a capacitor value of 0.1 µF is enough in this condition. improve PSRR while a quick-start circuit fast-charges When it is difficult to place these two ground points this capacitor at startup. The combination of high close together, a 1 µF capacitor is recommended. performance and low ground current also make the This capacitor counteracts reactive input sources and TPS734xx an excellent choice for portable improves transient response, noise rejection, and applications. All versions have thermal and ripple rejection. A higher-value capacitor may be over-current protection and are fully specified from necessary if large, fast rise-time load transients are –40°C to +125°C. anticipated, or if the device is located several inches from the power source. If source impedance is not Figure 20 shows the basic circuit connections for sufficiently low, a 0.1 µF input capacitor may be fixed voltage models. Figure 21 gives the connections necessary to ensure stability. for the adjustable output version (TPS73401). R1 and R2 can be calculated for any output voltage using the The TPS734xx is designed to be stable with standard formula in Figure 21. ceramic output capacitors of values 2.2 µF or larger. X5R and X7R type capacitors are best because they have minimal variation in value and ESR over temperature. Maximum ESR of the output capacitor should be < 1.0 Ω, so output capacitor type should be either ceramic or conductive polymer electrolytic. (TPS73401 only) The feedback capacitor, CFB, shown in Figure 21 is required for stability. For a parallel combination of R1 and R2 equal to 250kΩ, any value from 3pF to 1nF can be used. Fixed voltage versions have an internal 30pF feedback capacitor that is quick-charged at Figure 20. Typical Application Circuit for start-up. The adjustable version does not have this FIxed Voltage Versions quick-charge circuit, so values below 5pF should be used to ensure fast startup; values above 47pF can be used to implement an output voltage soft-start. Larger value capacitors also improve noise slightly. The TPS73401 is stable in unity-gain configuration (OUT tied to FB) without CFB. In most LDOs, the bandgap is the dominant noise source. If a noise reduction capacitor (CNR) is used with the TPS734xx, the bandgap does not contribute significantly to noise. Instead, noise is dominated by the output resistor divider and the error amplifier Figure 21. Typical Application Circuit for input. To minimize noise in a given application, use a Adjustable Voltage Versions 0.01 µF noise reduction capacitor; for the adjustable version, smaller value resistors in the output resistor space divider reduce noise. A parallel combination that gives 2 µA of divider current has the same noise space performance as a fixed voltage version. To further 8 Submit Documentation Feedback Copyright © 2007–2009, Texas Instruments Incorporated |
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