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TPS78618DCQR Datasheet(PDF) 9 Page - Texas Instruments |
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TPS78618DCQR Datasheet(HTML) 9 Page - Texas Instruments |
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9 / 17 page  www.ti.com APPLICATION INFORMATION GND EN NR IN OUT V IN V OUT 0.01 µF 2.2 µF TPS786xx 1 µF Board Layout Recommendation to Improve External Capacitor Requirements Regulator Mounting TPS78601, TPS78618 TPS78625, TPS78628 TPS78630, TPS78633 SLVS389D – SEPTEMBER 2002 – REVISED OCTOBER 2004 flow out of the NR pin must be at a minimum, The TPS786xx family of low-dropout (LDO) regulators because any leakage current creates an IR drop has been optimized for use in noise-sensitive equip- across the internal resistor, thus creating an output ment. The device features extremely low dropout error. Therefore, the bypass capacitor must have voltages, high PSRR, ultralow output noise, low minimal leakage current. The bypass capacitor quiescent current (265 µA typically), and enable input should be no more than 0.1-µf to ensure that it is fully to reduce supply currents to less than 1 µA when the charged during the quickstart time provided by the regulator is turned off. internal switch shown in the functional block diagram. A typical application circuit is shown in Figure 24. For example, the TPS78630 exhibits only 48 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 24. Typical Application Circuit PSRR and Noise Performance To improve ac measurements like PSRR, output noise, and transient response, it is recommended that A 2.2-µF or larger ceramic input bypass capacitor, the board be designed with separate ground planes connected between IN and GND and located close to for VIN and VOUT, with each ground plane connected the TPS786xx, is required for stability and improves only at the ground pin of the device. In addition, the transient response, noise rejection, and ripple rejec- ground connection for the bypass capacitor should tion. A higher-value input capacitor may be necessary connect directly to the ground pin of the device. if large, fast-rise-time load transients are anticipated and the device is located several inches from the power source. Like most low dropout regulators, the TPS786xx 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 1 soldered directly to a circuit-board copper area. 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 TPS786xx 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 9 |
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