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TPS76825QPWPR Datasheet(PDF) 11 Page - Texas Instruments |
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TPS76825QPWPR Datasheet(HTML) 11 Page - Texas Instruments |
11 / 23 page www.ti.com APPLICATION INFORMATION DEVICE OPERATION MINIMUM LOAD REQUIREMENTS FB - PIN CONNECTION (ADJUSTABLE VERSION ONLY) EXTERNAL CAPACITOR REQUIREMENTS TPS768xxQ SLVS211L – JUNE 1999 – REVISED JANUARY 2006 The TPS768xxQ family includes eight fixed-output voltage regulators (1.5 V, 1.8 V, 2.5 V, 2.7 V, 2.8 V, 3.0 V, 3.3 V, and 5.0 V), and offers an adjustable device, the TPS76801 (adjustable from 1.2 V to 5.5 V). The TPS768xxQ features very low quiescent current, which remains virtually constant even with varying loads. Conventional LDO regulators use a PNP pass element, the base current of which is directly proportional to the load current through the regulator (IB = IC/β). The TPS768xxQ uses a PMOS transistor to pass current; because the gate of the PMOS is voltage driven, operating current is low and invariable over the full load range. Another pitfall associated with the PNP-pass element is its tendency to saturate when the device goes into dropout. The resulting drop in β forces an increase in I B to maintain the load. During power up, this translates to large start-up currents. Systems with limited supply current may fail to start up. In battery-powered systems, it means rapid battery discharge when the voltage decays below the minimum required for regulation. The TPS768xxQ quiescent current remains low even when the regulator drops out, eliminating both problems. The TPS768xxQ family also features a shutdown mode that places the output in the high-impedance state (essentially equal to the feedback-divider resistance) and reduces quiescent current to 2 µA. If the shutdown feature is not used, EN should be tied to ground. The TPS768xxQ family is stable even at zero load; no minimum load is required for operation. The FB pin is an input pin to sense the output voltage and close the loop for the adjustable option. The output voltage is sensed through a resistor divider network to close the loop as shown in Figure 27. Normally, this connection should be as short as possible; however, the connection can be made near a critical circuit to improve performance at that point. Internally, FB connects to a high-impedance wide-bandwidth amplifier and noise pickup feeds through to the regulator output. Routing the FB connection to minimize/avoid noise pickup is essential. An input capacitor is not usually required; however, a ceramic bypass capacitor (0.047 µF or larger) improves load transient response and noise rejection if the TPS768xxQ is located more than a few inches from the power supply. A higher-capacitance electrolytic capacitor may be necessary if large (hundreds of milliamps) load transients with fast rise times are anticipated. Like all low dropout regulators, the TPS768xxQ requires an output capacitor connected between OUT and GND to stabilize the internal control loop. The minimum recommended capacitance value is 10 µF and the ESR (equivalent series resistance) must be between 60 m Ω and 1.5 Ω. Capacitor values 10 µF or larger are acceptable, provided the ESR is less than 1.5 Ω . Solid tantalum electrolytic, aluminum electrolytic, and multilayer ceramic capacitors are all suitable, provided they meet the requirements described above. 11 Submit Documentation Feedback |
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