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TPS79932YZUR Datasheet(PDF) 10 Page - Texas Instruments |
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TPS79932YZUR Datasheet(HTML) 10 Page - Texas Instruments |
10 / 21 page www.ti.com APPLICATION INFORMATION Feedback Capacitor Requirements Output Noise Input and Output Capacitor Requirements TPS799xx GND EN NR IN OUT V IN V OUT Optional input capacitor. May improve source impedance, noise, or PSRR. Optional bypass capacitor to reduce output noise and increase PSRR. 2.2 µF Ceramic V EN TPS799xx GND EN FB IN OUT V IN V OUT R 1 C FB R 2 Optional input capacitor. May improve source impedance, noise, or PSRR. V OUT = × 1.193 (R 1 + R2) R 2 V EN 2.2 µF Ceramic TPS799xx SBVS056G – JANUARY 2005 – REVISED AUGUST 2006 The TPS799xx family of LDO regulators combines The TPS799xx is designed to be stable with the high performance required of many RF and standard ceramic capacitors of values 2.2 µF or precision analog applications with ultra-low current larger. X5R and X7R type capacitors are best as consumption. High PSRR is provided by a high gain, they have minimal variation in value and ESR over high bandwidth error loop with good supply rejection temperature. Maximum ESR should be < 1.0 Ω. at very low headroom (VIN – VOUT). Fixed voltage versions provide a noise reduction pin to bypass noise generated by the bandgap reference and to (TPS79901 only) improve PSRR while a quick-start circuit fast-charges The feedback capacitor, CFB, shown in Figure 29 is this capacitor at startup. The combination of high required for stability. For a parallel combination of R1 performance and low ground current also make the and R2 equal to 250kΩ, any value from 3pF to 1nF TPS799xx an excellent choice for portable can be used. Fixed voltage versions have an internal applications. All versions have thermal and 30pF feedback capacitor which is quick-charged at over-current protection and are fully specified from start-up. The adjustable version does not have this –40 °C to +125°C. quick-charge circuit, so values below 5pF should be Figure 28 shows the basic circuit connections for used to ensure fast startup; values above 47pF can fixed voltage models. Figure 29 gives the be used to implement an output voltage soft-start. connections for the adjustable output version Larger value capacitors also improve noise slightly. (TPS79901). R1 and R2 can be calculated for any The TPS79901 is stable in unity-gain configuration output voltage using the formula in Figure 29. (OUT tied to FB) without CFB. Sample resistor values for common output voltages are shown in Figure 29. In most LDOs, the bandgap is the dominant noise source. If a noise reduction capacitor (CNR) is used Although an input capacitor is not required for with the TPS799xx, the bandgap does not contribute stability, it is good analog design practice to connect significantly to noise. Instead, noise is dominated by a 0.1 µF to 1µF low ESR capacitor across the input the output resistor divider and the error amplifier supply near the regulator. This will counteract input. To minimize noise in a given application, use a reactive input sources and improve transient 0.01 µF noise reduction capacitor; for the adjustable response, noise rejection, and ripple rejection. A version, smaller value resistors in the output resistor higher-value capacitor may be necessary if large, divider reduce noise. A parallel combination that fast rise-time load transients are anticipated or the gives 2 µA of divider current will have the same noise device is located several inches from the power performance as a fixed voltage version. To further source. If source impedance is not sufficiently low, a optimize noise, equivalent series resistance of the 0.1 µF input capacitor may be necessary to ensure output capacitor can be set to approximately 0.2 Ω. stability. This configuration maximizes phase margin in the control loop, reducing total output noise by up to 10%. Figure 28. Typical Application Circuit for Figure 29. Typical Application Circuit for Fixed Voltage Versions Adjustable Voltage Version 10 Submit Documentation Feedback |
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