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TPS79433DCQR Datasheet(PDF) 9 Page - Texas Instruments |
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TPS79433DCQR Datasheet(HTML) 9 Page - Texas Instruments |
9 / 15 page www.ti.com APPLICATION INFORMATION TPS794xx GND EN NR IN OUT V IN V OUT 0.1 µF 0.01 µF 2.2 µF External Capacitor Requirements TPS79401, TPS79418 TPS79425, TPS79428 TPS79430, TPS79433 SLVS349D – NOVEMBER 2001 – REVISED OCTOBER 2004 The TPS794xx family of low-dropout (LDO) regulators has been optimized for use in noise-sensitive equipment. The device features extremely low dropout voltages, high PSRR, ultralow output noise, low quiescent current, and enable input to reduce supply currents to less than 1 µA when the regulator is turned off. A typical application circuit is shown in Figure 22. Figure 22. Typical Application Circuit A 0.1-µF or larger ceramic input bypass capacitor, connected between IN and GND and located close to the TPS794xx, is required for stability. It improves transient response, noise rejection, and ripple rejection. A higher-value input capacitor may be necessary if large, fast-rise-time load transients are anticipated or the device is located several inches from the power source. Like most low dropout regulators, the TPS794xx requires an output capacitor connected between OUT and GND to stabilize the internal control loop. The minimum recommended capacitance is 2.2 µF. Any 2.2 µF or larger ceramic capacitor is suitable. The internal voltage reference is a key source of noise in an LDO regulator. The TPS794xx 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 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, because any leakage current creates an IR drop across the internal resistor thus creating an output error. Therefore, the NR capacitor must have minimal leakage current. The bypass capacitor should be no more than 0.1 µF to ensure that it is fully charged during the quickstart time provided by the internal switch shown in the functional block diagram. For example, the TPS79428 exhibits only 32 µVRMS of output voltage noise using a 0.1-µF ceramic NR capacitor and a 2.2-µF ceramic output capacitor. Note that the output starts up slower as the bypass capacitance increases due to the RC time constant at the NR pin that is created by the internal 250-k Ω resistor and external capacitor. 9 |
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