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TPS79625DCQ Datasheet(PDF) 8 Page - Texas Instruments |
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TPS79625DCQ Datasheet(HTML) 8 Page - Texas Instruments |
8 / 33 page www.ti.com APPLICATION INFORMATION Board Layout Recommendation to Improve GND EN NR IN OUT V IN V OUT 0.01 µF TPS796xx 2.2 µF 1 µF External Capacitor Requirements Regulator Mounting Programming the TPS79601 Adjustable LDO V OUT + VREF 1) R1 R2 (1) TPS796xx SLVS351I – SEPTEMBER 2002 – REVISED MAY 2006 The TPS796xx family of low-dropout (LDO) For example, the TPS79630 exhibits 40 µV RMS of regulators has been optimized for use in output voltage noise using a 0.1 µF ceramic bypass noise-sensitive equipment. The device features capacitor and a 10 µF ceramic output capacitor. Note extremely low dropout voltages, high PSRR, ultralow that the output starts up slower as the bypass output noise, low quiescent current (265 µA typically), capacitance increases due to the RC time constant and enable input to reduce supply currents to less at the bypass pin that is created by the internal than 1 µA when the regulator is turned off. 250k Ω resistor and external capacitor. A typical application circuit is shown in Figure 22. PSRR and Noise Performance 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 connected only at the ground pin of the device. In Figure 22. Typical Application Circuit addition, the ground connection for the bypass capacitor should connect directly to the ground pin of the device. Although not required, it is good analog design practice to place a 0.1 µF — 2.2µF capacitor near the The tab of the SOT223-6 package is electrically input of the regulator to counteract reactive input connected to ground. For best thermal performance, sources. A 2.2 µF or larger ceramic input bypass the tab of the surface-mount version should be capacitor, connected between IN and GND and soldered directly to a circuit-board copper area. located close to the TPS796xx, is required for Increasing the copper area improves heat stability and improves transient response, noise dissipation. rejection, and ripple rejection. A higher-value input capacitor may be necessary if large, fast-rise-time Solder pad footprint recommendations for the load transients are anticipated and the device is devices are presented in an application bulletin located several inches from the power source. Solder Pad Recommendations for Surface-Mount Devices, literature number AB-132, available for Like most low dropout regulators, the TPS796xx download from the TI web site (www.ti.com). requires an output capacitor connected between OUT and GND to stabilize the internal control loop. The minimum recommended capacitor is 1 µF. Any Regulator 1 µF or larger ceramic capacitor is suitable. The output voltage of the TPS79601 adjustable The internal voltage reference is a key source of regulator is programmed using an external resistor noise in an LDO regulator. The TPS796xx has an divider as shown in Figure 28. The output voltage is NR pin which is connected to the voltage reference calculated using Equation 1: through a 250k Ω internal resistor. The 250kΩ 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 where: and, therefore, the noise at the regulator output. In order for the regulator to operate properly, the • VREF = 1.2246V typ (the internal reference current flow out of the NR pin must be at a minimum, voltage) because any leakage current creates an IR drop Resistors R1 and R2 should be chosen for across the internal resistor, thus creating an output approximately 40 µA divider current. Lower value error. Therefore, the bypass capacitor must have resistors can be used for improved noise minimal leakage current. The bypass capacitor performance, but the device wastes more power. should be no more than 0.1 µF in order to ensure that Higher values should be avoided, as leakage current it is fully charged during the quickstart time provided at FB increases the output voltage error. by the internal switch shown in the functional block diagram. 8 Submit Documentation Feedback |
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