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TPS79618DCQR Datasheet(PDF) 9 Page - Texas Instruments |
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TPS79618DCQR Datasheet(HTML) 9 Page - Texas Instruments |
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9 / 30 page  V OUT + VREF 1) R1 R2 GND EN NR IN OUT V IN V OUT 0.01 µF TPS796xx 2.2 µF 1 µF TPS796 www.ti.com SLVS351O – SEPTEMBER 2002 – REVISED NOVEMBER 2013 APPLICATION INFORMATION The TPS796xx family of low-dropout (LDO) regulators For example, the TPS79630 exhibits 40 μVRMS of has been optimized for use in noise-sensitive output voltage noise using a 0.1 μF ceramic bypass equipment. The device features extremely low capacitor and a 10 μF ceramic output capacitor. Note dropout voltages, high PSRR, ultralow output noise, that the output starts up slower as the bypass low quiescent current (265 μA typically), and enable capacitance increases due to the RC time constant at input to reduce supply currents to less than 1 μA the bypass pin that is created by the internal 250k Ω when the regulator is turned off. resistor and external capacitor. A typical application circuit is shown in Figure 22. Board Layout Recommendation to Improve 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 addition, the Figure 22. Typical Application Circuit ground connection for the bypass capacitor should connect directly to the ground pin of the device. External Capacitor Requirements Regulator Mounting Although not required, it is good analog design The tab of the SOT223-6 package is electrically practice to place a 0.1 μF to 2.2μF capacitor near the connected to ground. For best thermal performance, input of the regulator to counteract reactive input the tab of the surface-mount version should be sources. A 2.2 μF or larger ceramic input bypass soldered directly to a circuit-board copper area. capacitor, connected between IN and GND and Increasing the copper area improves heat dissipation. located close to the TPS796xx, is required for stability and improves transient response, noise rejection, and Solder pad footprint recommendations for the devices ripple rejection. A higher-value input capacitor may be are presented in an application bulletin Solder Pad necessary if large, fast-rise-time load transients are Recommendations for Surface-Mount Devices, anticipated and the device is located several inches literature number AB-132, available for download from the power source. from the TI web site (www.ti.com). Like most low dropout regulators, the TPS796xx Programming the TPS79601 Adjustable LDO requires an output capacitor connected between OUT Regulator and GND to stabilize the internal control loop. The minimum recommended capacitor is 1 μF. Any 1μF or The output voltage of the TPS79601 adjustable larger ceramic capacitor is suitable. regulator is programmed using an external resistor divider (see Figure 23). The output voltage is The internal voltage reference is a key source of calculated using Equation 1: noise in an LDO regulator. The TPS796xx has an NR pin which is connected to the voltage reference through a 250k Ω internal resistor. The 250kΩ internal (1) resistor, in conjunction with an external bypass where: capacitor connected to the NR pin, creates a low- • VREF = 1.2246V typ (the internal reference pass filter to reduce the voltage reference noise and, voltage) therefore, the noise at the regulator output. In order for the regulator to operate properly, the current flow Resistors R1 and R2 should be chosen for out of the NR pin must be at a minimum, because approximately 40 μA divider current. Lower value any leakage current creates an IR drop across the resistors can be used for improved noise internal resistor, thus creating an output error. performance, but the device wastes more power. Therefore, the bypass capacitor must have minimal Higher values should be avoided, as leakage current leakage current. The bypass capacitor should be no at FB increases the output voltage error. more than 0.1 μF in order to ensure that it is fully charged during the quickstart time provided by the internal switch shown in the functional block diagram. Copyright © 2002–2013, Texas Instruments Incorporated Submit Documentation Feedback 9 |
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