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TPS78601DCQR Datasheet(PDF) 10 Page - Texas Instruments |
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TPS78601DCQR Datasheet(HTML) 10 Page - Texas Instruments |
10 / 29 page V IN V OUT 2.2 F m 0.01 F m 2.2 F m IN EN GND OUT NR TPS786xx TPS786xx SLVS389L – SEPTEMBER 2002 – REVISED OCTOBER 2010 www.ti.com APPLICATION INFORMATION order for the regulator to operate properly, the current The TPS786xx family of low-dropout (LDO) regulators flow out of the NR pin must be at a minimum, has been optimized for use in noise-sensitive because any leakage current creates an IR drop equipment. The device features extremely low across the internal resistor, thus creating an output dropout voltages, high PSRR, ultralow output noise, error. Therefore, the bypass capacitor must have low quiescent current (265 mA, typically), and enable minimal leakage current. The bypass capacitor input to reduce supply currents to less than 1 mA should be no more than 0.1-mF to ensure that it is when the regulator is turned off. fully charged during the quickstart time provided by the internal switch shown in the functional block A typical application circuit is shown in Figure 24. diagram. For example, the TPS78630 exhibits only 48 mVRMS of output voltage noise using a 0.1-mF ceramic bypass capacitor and a 10-mF ceramic output capacitor. Note that the output starts up slower as the bypass capacitance increases due to the RC time constant at the bypass pin that is created by the internal 250-k Ω resistor and external capacitor. Figure 24. Typical Application Circuit BOARD LAYOUT RECOMMENDATIONS TO IMPROVE PSRR AND NOISE PERFORMANCE EXTERNAL CAPACITOR REQUIREMENTS To improve ac measurements like PSRR, output A 2.2-mF or larger ceramic input bypass capacitor, noise, and transient response, it is recommended that connected between IN and GND and located close to the board be designed with separate ground planes the TPS786xx, is required for stability and improves for VIN and VOUT, with each ground plane connected transient response, noise rejection, and ripple only at the ground pin of the device. In addition, the rejection. A higher-value input capacitor may be ground connection for the bypass capacitor should necessary if large, fast-rise-time load transients are connect directly to the ground pin of the device. anticipated and the device is located several inches from the power source. REGULATOR MOUNTING Like most low-dropout regulators, the TPS786xx The tab of the SOT223-6 package is electrically requires an output capacitor connected between OUT connected to ground. For best thermal performance, and GND to stabilize the internal control loop. The the tab of the surface-mount version should be minimum recommended capacitor is 1 mF. Any 1 mF soldered directly to a circuit-board copper area. or larger ceramic capacitor is suitable. Increasing the copper area improves heat dissipation. The internal voltage reference is a key source of Solder pad footprint recommendations for the devices noise in an LDO regulator. The TPS786xx has an NR are presented in Application Report SBFA015, Solder pin which is connected to the voltage reference Pad Recommendations for Surface-Mount Devices, through a 250-k Ω internal resistor. The 250-kΩ available from the TI web site at www.ti.com. internal resistor, in conjunction with an external bypass capacitor connected to the NR pin, creates a low pass filter to reduce the voltage reference noise and, therefore, the noise at the regulator output. In 10 Submit Documentation Feedback Copyright © 2002–2010, Texas Instruments Incorporated Product Folder Link(s): TPS786xx |
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