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TPS74401RGWRG4 Datasheet(PDF) 10 Page - Texas Instruments |
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TPS74401RGWRG4 Datasheet(HTML) 10 Page - Texas Instruments |
10 / 22 page www.ti.com APPLICATION INFORMATION INPUT, OUTPUT, AND BIAS CAPACITOR TRANSIENT RESPONSE TPS74401 GND EN FB IN PG SS OUT V IN V OUT V PG R 1 R 2 R 3 C OUT Optional C IN 1 F m C SS V BIAS C BIAS 1 F m V =0.8 OUT ´ 1+ R 1 R 2 ( ) BIAS TPS74401 SBVS066D – DECEMBER 2005 – REVISED AUGUST 2006 The TPS74401 belongs to a family of new REQUIREMENTS generation ultra-low dropout regulators that feature soft-start and tracking capabilities. These regulators The device does not require any output capacitor for use a low current bias input to power all internal stability. If an output capacitor is needed, the device control circuitry, allowing the NMOS pass transistor is designed to be stable for all available types and to regulate very low input and output voltages. values of output capacitance. The device is also stable with multiple capacitors in parallel, of any type The use of an NMOS-pass FET offers several critical or value. advantages for many applications. Unlike a PMOS topology device, the output capacitor has little effect The capacitance required on the IN and BIAS pins on loop stability. This architecture allows the strongly depends on the input supply source TPS74401 to be stable with any or even no output impedance. To counteract any inductance in the capacitor. Transient response is also superior to input, the minimum recommended capacitor for VIN PMOS topologies, particularly for low VIN and VBIAS is 1µF. If VIN and VBIAS are connected to applications. the same supply, the recommended minimum capacitor for VBIAS is 4.7µF. Good quality, low ESR The TPS74401 features a programmable, capacitors should be used on the input; ceramic X5R voltage-controlled soft-start circuit that provides a and X7R capacitors are preferred. These capacitors smooth, monotonic start-up and limits startup inrush should be placed as close the pins as possible for currents that may be caused by large capacitive optimum performance. loads. A power-good (PG) output is available to allow supply monitoring and sequencing of other supplies. An enable (EN) pin with hysteresis and deglitch allows slow-ramping signals to be used for The TPS74401 was designed to have transient sequencing the device. The low VIN and VOUT response within 5% for most applications without any capability allows for inexpensive, easy-to-design, and output capacitor. In some cases, the transient efficient linear regulation between the multiple supply response may be limited by the transient response of voltages often present in processor intensive the input supply. This limitation is especially true in systems. applications where the difference between the input and output is less than 300mV. In this case, adding Figure 27 illustrates a typical application circuit for additional input capacitance improves the transient the TPS74401 adjustable input device. response much more than just adding additional R1 and R2 can be calculated for any output voltage output capacitance. With a solid input supply, adding using the formula shown in Figure 27. Refer to additional output capacitance reduces undershoot Table 1 for sample resistor values of common output and overshoot during a transient at the expense of a voltages. In order to achieve the maximum accuracy slightly longer VOUT recovery time. Refer to Figure 16 specifications, R2 should be ≤ 4.99kΩ. in the Typical Characteristics section. Since the TPS74401 is stable without an output capacitor, many applications may allow for little or no capacitance at the LDO output. For these applications, local bypass capacitance for the device under power may be sufficient to meet the transient requirements of the application. This design reduces the total solution cost by avoiding the need to use expensive high-value capacitors at the LDO output. Figure 27. Typical Application Circuit for the TPS74401 (Adjustable) 10 Submit Documentation Feedback |
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