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REG103FA-3.3KTTT Datasheet(PDF) 8 Page - Texas Instruments |
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REG103FA-3.3KTTT Datasheet(HTML) 8 Page - Texas Instruments |
8 / 26 page REG103 8 SBVS010D BASIC OPERATION The REG103 series is a family of LDO (Low Drop-Out) linear regulators. The family includes five fixed output versions (2.5V to 5.0V) and an adjustable output version. An internal DMOS power device provides low dropout regula- tion with near constant ground pin current (largely indepen- dent of load and drop-out conditions) and very fast line and load transient response. All versions include internal current limit and thermal shutdown circuitry. Figure 1 shows the basic circuit connections for the fixed voltage models. Figure 2 gives the connections for the adjustable output version (REG103A) and example resistor values for some commonly used output voltages. Values for other voltages can be calculated from the equation shown in Figure 2. The SO-8 package provides two pins each for VIN and VOUT. Both sets of pins MUST be used and connected adjacent to the device. FIGURE 1. Fixed Voltage Nominal Circuit for REG103. REG103 ENABLE V OUT C OUT V IN 0.1 µF C NR 0.01 µF ERROR Gnd NR In Out Optional None of the versions require an output capacitor for regula- tor stability. The REG103 will accept any output capacitor type less than 1 µF. For capacitance values larger than 1µF, the effective ESR should be greater than 0.1 Ω. This mini- mum ESR value includes parasitics such as printed circuit board traces, solder joints, and sockets. A minimum 0.1 µF low ESR capacitor connected to the input supply voltage is recommended. INTERNAL CURRENT LIMIT The REG103 internal current limit has a typical value of 700mA. A fold-back feature limits the short-circuit current to a typical short-circuit value of 40mA. This circuit will protect the regulator from damage under all load conditions. A typical characteristic of VOUT versus IOUT is given in Figure 3a. Care should be taken in high current applications to avoid ground currents flowing in the circuit board traces causing voltage drops between points on the circuit. If voltage drops occur on the circuit board ground that causes the load ground voltage to be much lower than the ground voltage seen by the ground pin on the REG103, the foldback current may approach zero and the REG103 may not start up. In these types of applications, a large value resistor can be placed between VIN and VOUT to help “boost” up the output of the REG103 during start-up, see Figure 3b. The value for the “boost” resistor should be chosen so that the current through the “boost” resistor is less than the minimum load current: RBOOST > (VIN – VOUT)/ILOAD. Typically, a good value for a “boost” resistor is 5k Ω. FIGURE 2. Adjustable Voltage Circuit for REG103A. V OUT = (1 + R1/R2) • 1.295V Pin numbers for SO-8 package. REG103 V IN 0.1 µF 4 7 8 Gnd V OUT R 1 C FB 0.01 µF C OUT Adj R 2 I ADJ Load 1 2 3 6 5 ERROR 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. V OUT (V) R 1 (Ω) (1) R 2 (Ω) (1) 1.295 Short Open 2.5 12.1k 13k 1.21k 1.3k 3 16.9k 13k 1.69k 1.3k 3.3 20k 13k 2.0k 1.3k 5 37.4k 13k 3.74k 1.3k NOTE: (1) Resistors are standard 1% values. EXAMPLE RESISTOR VALUES Optional |
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