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TPS79525 Datasheet(PDF) 9 Page - Texas Instruments |
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TPS79525 Datasheet(HTML) 9 Page - Texas Instruments |
9 / 15 page www.ti.com APPLICATION INFORMATION GND EN NR IN OUT V IN V OUT 0.01 µF 2.2 µF 1 µF TPS795xx Board Layout Recommendation to Improve External Capacitor Requirements Regulator Mounting TPS79501, TPS79516 TPS79518, TPS79525 TPS79530, TPS79533 SLVS350C – OCTOBER 2002 – REVISED JANUARY 2005 because any leakage current creates an IR drop The TPS795xx family of low-dropout (LDO) regulators across the internal resistor thus creating an output has been optimized for use in noise-sensitive equip- error. Therefore, the bypass capacitor must have ment. The device features extremely low dropout minimal leakage current. The bypass capacitor voltages, high PSRR, ultralow output noise, low should be no more than 0.1-µF in order to ensure that quiescent current (265 µA typically), and enable input it is fully charged during the quickstart time provided to reduce supply currents to less than 1 µA when the by the internal switch shown in the functional block regulator is turned off. diagram. A typical application circuit is shown in Figure 23. For example, the TPS79530 exhibits only 33 µVRMS of output voltage noise using a 0.1-µF ceramic bypass capacitor and a 10-µF ceramic output capaci- tor. 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 23. Typical Application Circuit PSRR and Noise Performance To improve ac measurements like PSRR, output A 1-µF 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 TPS795xx, is required for stability and improves for VIN and VOUT, with each ground plane connected transient response, noise rejection, and ripple rejec- only at the ground pin of the device. In addition, the tion. A higher-value input capacitor may be necessary ground connection for the bypass capacitor should if large, fast-rise-time load transients are anticipated connect directly to the ground pin of the device. and the device is located several inches from the power source. Like most low dropout regulators, the TPS795xx 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 capacitance is 1 µF. Any soldered directly to a circuit-board copper area. 1 µF 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 TPS795xx has an NR are presented in an application bulletin Solder Pad pin which is connected to the voltage reference Recommendations for Surface-Mount Devices, litera- through a 250-k Ω internal resistor. The 250-kΩ ture number AB-132, available from the TI web site internal resistor, in conjunction with an external by- (www.ti.com). pass 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 order for the regulator to operate properly, the current flow out of the NR pin must be at a minimum, 9 |
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