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TPS749XX Datasheet(PDF) 10 Page - Texas Instruments |
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TPS749XX Datasheet(HTML) 10 Page - Texas Instruments |
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10 / 27 page  www.ti.com APPLICATION INFORMATION INPUT, OUTPUT, AND BIAS CAPACITOR TRANSIENT RESPONSE V OUT C OUT 10 F m TPS74901 GND EN FB IN PG BIAS SS OUT V IN R 1 R 2 R 3 C IN 1 F m C SS V BIAS C BIAS 1 F m V =0.8 OUT ´ 1+ R 1 R 2 ) ( TPS749xx SBVS082A – JUNE 2007 – REVISED JULY 2007 The TPS749xx belongs to a family of low dropout REQUIREMENTS regulators that feature soft-start capabilities. These regulators use a low current bias input to power all The device is designed to be stable for all available internal control circuitry, allowing the NMOS pass types of and values of output capacitors ≥ 2.2μF. transistor to regulate very low input and output The device is also stable with multiple capacitors in voltages. parallel, which can be of any type or value. The use of an NMOS-pass FET offers several critical The capacitance required on the IN and BIAS pin advantages for many applications. Unlike a PMOS strongly depends on the input supply source topology device, the output capacitor has little effect impedance. To counteract any inductance in the on loop stability. This architecture allows the input, the minimum recommended capacitor for VIN TPS749xx to be stable with any capacitor type of and VBIAS is 1μF. If VIN and VBIAS are connected to value 2.2 μF or greater. Transient response is also the same supply, the recommended minimum superior to PMOS topologies, particularly for low VIN capacitor for VBIAS is 4.7μF. Good quality, low ESR applications. capacitors should be used on the input; ceramic X5R and X7R capacitors are preferred. These capacitors The TPS749xx features a programmable should be placed as close the pins as possible for voltage-controlled soft-start circuit that provides a optimum performance. smooth, monotonic start-up and limits startup inrush currents that may be caused by large capacitive loads. A power-good (PG) output is available to allow supply monitoring and sequencing of other supplies. The TPS749xx is designed to have excellent An enable (EN) pin with hysteresis and deglitch transient response for most applications with a small allows slow-ramping signals to be used for amount of output capacitance. In some cases, the sequencing the device. The low VIN and VOUT transient response may be limited by the transient capability allows for inexpensive, easy-to-design, and response of the input supply. This limitation is efficient linear regulation between the multiple supply especially true in applications where the difference voltages often present in processor intensive between the input and output is less than 300mV. In systems. this case, adding additional input capacitance improves the transient response much more than just Figure 25 illustrates the typical application circuit for adding additional output capacitance would do. With the TPS749xx adjustable input device. a solid input supply, adding additional output R1 and R2 can be calculated for any output voltage capacitance reduces undershoot and overshoot using the formula shown in Figure 25. Refer to during a transient event; refer to Figure TBD in the Table 1 for sample resistor values of common output Typical Characteristics section. Because the voltages. In order to achieve the maximum accuracy TPS749xx is stable with output capacitors as low as specifications, R2 should be ≤ 4.99kΩ. 2.2 μF, many applications may need very little capacitance at the LDO output. For these applications, local bypass capacitance for the powered device 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 25. Typical Application Circuit for the TPS749xx (Adjustable) 10 Submit Documentation Feedback |
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