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TPS79901DRVR Fiches technique(PDF) 10 Page - Texas Instruments |
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TPS79901DRVR Fiches technique(HTML) 10 Page - Texas Instruments |
10 / 21 page www.ti.com APPLICATION INFORMATION 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 Input and Output Capacitor Requirements Feedback Capacitor Requirements (TPS79901 only) TPS799xx SBVS056E – JANUARY 2005 – REVISED OCTOBER 2005 The TPS799xx family of LDO regulators combines the high performance required of many RF and precision analog applications with ultra-low current consumption. High PSRR is provided by a high gain, high bandwidth error loop with good supply rejection at very low headroom (VIN – VOUT). Fixed voltage versions provide a noise reduction pin to bypass noise generated by the bandgap reference and to improve PSRR while a quick-start circuit fast-charges this capacitor at startup for quick startup times. The combination of high performance and low ground current also make the TPS799xx an excellent choice for portable applications. All versions have thermal and over-current protection and are fully specified from –40°C to +125°C. Figure 28 shows the basic circuit connections for fixed voltage models. Figure 29 gives the connections for the adjustable output version (TPS79901). R1 and R2 can be calculated for any output voltage using the formula in Figure 29. Sample resistor values for common output voltages are shown in Figure 29. Figure 28. Typical Application Circuit for Figure 29. Typical Application Circuit for Fixed Voltage Versions Adjustable Voltage Version Although an input capacitor is not required for stability, it is good analog design practice to connect a 0.1µF to 1µF low ESR capacitor across the input supply near the regulator. This will counteract reactive input sources and improve transient response, noise rejection, and ripple rejection. A higher-value capacitor may be necessary if large, fast rise-time load transients are anticipated or the device is located several inches from the power source. If source impedance is not sufficiently low, a 0.1µF input capacitor may be necessary to ensure stability. The TPS799xx is designed to be stable with standard ceramic capacitors of values 2.2µF or larger. X5R and X7R type capacitors are best as they have minimal variation in value and ESR over temperature. Maximum ESR should be < 1.0 Ω. The feedback capacitor, CFB, shown in Figure 29 is required for stability. For a parallel combination of R1 and R2 equal to 250k Ω, any value from 3pF to 1nF can be used. Fixed voltage versions have an internal 30pF feedback capacitor which is quick-charged at start-up. The adjustable version does not have this 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 TPS79901 is stable in unity-gain configuration (OUT tied to FB) without CFB. 10 |
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