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TPS78618KTTT Datasheet(PDF) 8 Page - Texas Instruments |
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TPS78618KTTT Datasheet(HTML) 8 Page - Texas Instruments |
8 / 21 page www.ti.com APPLICATION INFORMATION BOARD LAYOUT RECOMMENDATIONS TO TPS786xx GND EN NR IN OUT V IN V OUT 0.1 µF 0.01 µF 2.2 µF EXTERNAL CAPACITOR REQUIREMENTS REGULATOR MOUNTING TPS786xx SLVS389G – SEPTEMBER 2002 – REVISED JULY 2006 because any leakage current creates an IR drop The TPS786xx 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 to ensure that it is output noise, low quiescent current (265 µA, fully charged during the quickstart time provided by typically), and enable input to reduce supply currents the internal switch shown in the functional block to less than 1 µA when the regulator is turned off. diagram. A typical application circuit is shown in Figure 24. For example, the TPS78630 exhibits only 48 µV RMS 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 due to 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 PERFORMANCE Figure 24. Typical Application Circuit To improve ac measurements like PSRR, output noise, and transient response, it is recommended that the board be designed with separate ground planes for VIN and VOUT, with each ground plane A 2.2- µF or larger ceramic input bypass capacitor, connected only at the ground pin of the device. In connected between IN and GND and located close addition, the ground connection for the bypass to the TPS786xx, is required for stability and capacitor should connect directly to the ground pin of improves transient response, noise rejection, and the device. ripple rejection. A higher-value input capacitor may be necessary if large, fast-rise-time load transients are anticipated and the device is located several inches from the power source. The tab of the SOT223-6 package is electrically connected to ground. For best thermal performance, Like most low-dropout regulators, the TPS786xx the tab of the surface-mount version should be requires an output capacitor connected between soldered directly to a circuit-board copper area. OUT and GND to stabilize the internal control loop. Increasing the copper area improves heat The minimum recommended capacitor is 1 µF. Any dissipation. 1 µF or larger ceramic capacitor is suitable. Solder pad footprint recommendations for the The internal voltage reference is a key source of devices are presented in Application Report noise in an LDO regulator. The TPS786xx has an SBFA015, Solder Pad Recommendations for NR pin which is connected to the voltage reference Surface-Mount Devices, available from the TI web through a 250-k Ω internal resistor. The 250-kΩ 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 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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