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REG101UA-2.8 Datasheet(PDF) 9 Page - Texas Instruments |
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REG101UA-2.8 Datasheet(HTML) 9 Page - Texas Instruments |
9 / 23 page REG101 9 SBVS026D BASIC OPERATION The REG101 series of LDO (Low Drop-Out) linear regula- tors offers a wide selection of fixed output voltage versions and an adjustable output version. The REG101 belongs to a family of new generation LDO regulators that utilize a DMOS pass transistor to achieve ultra-low dropout perfor- mance and freedom from output capacitor constraints. Ground pin current remains under 650 µA over all line, load, and temperature conditions. All versions have thermal and over- current protection, including foldback current limit. The REG101 does not require an output capacitor for regu- lator stability and is stable over most output currents and with almost any value and type of output capacitor up to 10 µF or more. For applications where the regulator output current drops below several milliamps, stability can be enhanced by: adding a 1k Ω to 2kΩ load resistor; using capacitance values less than 10 µF; or keeping the effective series resistance greater than 0.05 Ω including the capacitor’s ESR and parasitic resistance in printed circuit board traces, solder joints, and sockets. Although an input capacitor is not required, it is good analog design practice to connect a 0.1 µF low ESR capacitor across FIGURE 1. Fixed Voltage Nominal Circuit for REG101. REG101 Enable V OUT C OUT V IN 0.1 µF C NR 0.01 µF Gnd NR In Out Optional the input supply voltage. This is recommended to improve ripple rejection by reducing input voltage ripple. Figure 1 shows the basic circuit connections for the fixed voltage models. Figure 2 gives the connections for the adjustable output version (REG101A) and example resistor values for some commonly used output voltages. Values for other voltages can be calculated from the equation shown in Figure 2. INTERNAL CURRENT LIMIT The REG101 internal current limit has a typical value of 170mA. A foldback feature limits the short-circuit current to a typical short-circuit value of 60mA. This helps to protect the regulator from damage under all load conditions. A characteristic of VOUT versus IOUT is given in Figure 3 and in the Typical Characteristics section. FIGURE 2. Adjustable Voltage Circuit for REG101A. FIGURE 3. Foldback Current Limit of the REG101-3.3 at 25 °C. 040 20 140 160 80 100 120 60 180 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0 Output Current (mA) FOLDBACK CURRENT LIMIT I CL I CL REG101-3.3 V OUT = (1 + R1/R2) • 1.267V Pin numbers for SOT23 package. REG101 V IN 0.1 µF 2 1 Gnd V OUT R 1 C FB 0.01 µF C OUT Adj R 2 I ADJ Load 5 4 3 Enable To reduce current through divider, increase resistor values (see table at right). As the impedance of the resistor divider increases, I ADJ (~200nA) may introduce an error. C FB improves noise and transient response. Optional V OUT (V) R 1 (W) (1) R 2 (Ω) (1) 2.5 11.3k 11.5k 1.13k 1.15k 3.0 15.8k 11.5k 1.58k 1.15k 3.3 18.7k 11.5k 1.87k 1.15k 5.0 34.0k 11.5k 3.40k 1.15k NOTE: (1) Resistors are standard 1% values. EXAMPLE RESISTOR VALUES |
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