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TPS79525DCQ Fiches technique(PDF) 8 Page - Texas Instruments |
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TPS79525DCQ Fiches technique(HTML) 8 Page - Texas Instruments |
8 / 23 page www.ti.com APPLICATION INFORMATION TPS795xx GND EN NR IN OUT V IN V OUT 1 F m 0.01 F m 1 F m BOARD LAYOUT RECOMMENDATION TO EXTERNAL CAPACITOR REQUIREMENTS REGULATOR MOUNTING TPS795xx SLVS350G – OCTOBER 2002 – REVISED JULY 2006 because any leakage current creates an IR drop The TPS795xx family of low-dropout (LDO) across the internal resistor, thus creating an output regulators has been optimized for use in error. Therefore, the bypass capacitor must have noise-sensitive equipment. The device features minimal leakage current. The bypass capacitor extremely low dropout voltages, high PSRR, ultralow should be no more than 0.1- µF in order to ensure output noise, low quiescent current (265 µA that it is fully charged during the quickstart time typically), and an enable input to reduce supply provided by the internal switch shown in the currents to less than 1 µA when the regulator is Functional Block Diagram. turned off. For example, the TPS79530 exhibits only 33 µV RMS A typical application circuit is shown in Figure 23. of output voltage noise using a 0.1- µF ceramic bypass capacitor and a 10- µF ceramic output capacitor. Note that the output starts up slower as the bypass capacitance increases because of the RC time constant at the bypass pin that is created by the internal 250-k Ω resistor and external capacitor. IMPROVE PSRR AND NOISE Figure 23. Typical Application Circuit PERFORMANCE To improve ac measurements such as PSRR, output noise, and transient response, it is recommended that the board be designed with separate ground Although not required, it is good analog design planes for VIN and VOUT, with each ground plane practice to place a 0.1 µF — 2.2µF capacitor near the connected only at the ground pin of the device. In input of the regulator to counteract reactive input addition, the ground connection for the bypass sources. A higher-value input capacitor may be capacitor should connect directly to the ground pin of necessary if large, fast-rise-time load transients are the device. anticipated 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 connected to ground. For best thermal performance, OUT and GND to stabilize the internal control loop. the tab of the surface-mount version should be The minimum recommended capacitor is 1 µF. Any 1 soldered directly to a circuit-board copper area. µF or larger ceramic capacitor is suitable. Increasing the copper area improves heat The internal voltage reference is a key source of dissipation. noise in an LDO regulator. The TPS795xx has an Solder pad footprint recommendations for the NR pin which is connected to the voltage reference devices are presented in Application Report through a 250-k Ω internal resistor. The 250-kΩ SBFA015, Solder Pad Recommendations for internal resistor, in conjunction with an external Surface-Mount Devices, available from the TI web bypass capacitor connected to the NR pin, creates a site (www.ti.com). 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, 8 Submit Documentation Feedback |
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Description similaire - TPS79525DCQ |
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