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TPS79618 Fiches technique(PDF) 9 Page - Texas Instruments |
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TPS79618 Fiches technique(HTML) 9 Page - Texas Instruments |
9 / 18 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 O + V REF 1 ) R1 R2 (1) TPS79601, TPS79618, TPS79625 TPS79628, TPS79630, TPS79633 SLVS351D – SEPTEMBER 2002 – REVISED OCTOBER 2004 The TPS796xx family of low-dropout (LDO) regulators For example, the TPS79630 exhibits 40 µVRMS of has been optimized for use in noise-sensitive equip- output voltage noise using a 0.1-µF ceramic bypass ment. The device features extremely low dropout capacitor and a 10-µF ceramic output capacitor. Note voltages, high PSRR, ultralow output noise, low that the output starts up slower as the bypass quiescent current (265 µA typically), and enable input capacitance increases due to the RC time constant at to reduce supply currents to less than 1 µA when the the bypass pin that is created by the internal 250-k Ω regulator is turned off. 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 addition, the Figure 22. Typical Application Circuit ground connection for the bypass capacitor should connect directly to the ground pin of the device. Although not required, it is good analog design The tab of the SOT223-6 package is electrically practice to place a 0.1-µF — 2.2-µF capacitor near connected to ground. For best thermal performance, the 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, litera- anticipated and the device is located several inches ture number AB-132, available for download from the from the power source. TI web site (www.ti.com). Like most low dropout regulators, the TPS796xx requires an output capacitor connected between OUT Regulator and GND to stabilize the internal control loop. The minimum recommended capacitance is 1 µF. Any The output voltage of the TPS79601 adjustable 1 µF or larger ceramic capacitor is suitable. regulator is programmed using an external resistor divider as shown in Figure 28. 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 250-k Ω internal resistor. The 250-kΩ internal resistor, in conjunction with an external by- where: pass capacitor connected to the NR pin, creates a low-pass filter to reduce the voltage reference noise • VREF = 1.2246 V typ (the internal reference and, therefore, the noise at the regulator output. In voltage) order for the regulator to operate properly, the current Resistors R1 and R2 should be chosen for approxi- flow out of the NR pin must be at a minimum, mately 40-µA divider current. Lower value resistors because any leakage current creates an IR drop can be used for improved noise performance, but the across the internal resistor, thus creating an output device wastes more power. Higher values should be error. Therefore, the bypass capacitor must have avoided, as leakage current at FB increases the minimal leakage current. The bypass capacitor output voltage error. should be no 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. 9 |
Numéro de pièce similaire - TPS79618 |
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Description similaire - TPS79618 |
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