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LT3012EFE-PBF Datasheet(PDF) 9 Page - Linear Technology |
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LT3012EFE-PBF Datasheet(HTML) 9 Page - Linear Technology |
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9 / 16 page  LT3012 9 3012fd APPLICATIONS INFORMATION The adjustable device is tested and specified with the ADJ pin tied to the OUT pin and a 5μA DC load (unless otherwise specified) for an output voltage of 1.24V. Speci- fications for output voltages greater than 1.24V will be proportional to the ratio of the desired output voltage to 1.24V; (VOUT/1.24V). For example, load regulation for an output current change of 1mA to 250mA is –7mV typical at VOUT = 1.24V. At VOUT = 12V, load regulation is: (12V/1.24V) • (–7mV) = –68mV Output Capacitance and Transient Response The LT3012 is designed to be stable with a wide range of output capacitors. The ESR of the output capacitor affects stability, most notably with small capacitors. A minimum output capacitor of 3.3μF with an ESR of 3Ω or less is recommended to prevent oscillations. The LT3012 is a micropower device and output transient response will be a function of output capacitance. Larger values of output capacitance decrease the peak deviations and provide Figure 1. Adjustable Operation improved transient response for larger load current changes. Bypass capacitors, used to decouple individual components powered by the LT3012, will increase the effective output capacitor value. Extra consideration must be given to the use of ceramic capacitors. Ceramic capacitors are manufactured with a variety of dielectrics, each with different behavior across temperature and applied voltage. The most common dielectrics used are specified with EIA temperature char- acteristic codes of Z5U, Y5V, X5R and X7R. The Z5U and Y5V dielectrics are good for providing high capacitances in a small package, but they tend to have strong voltage and temperature coefficients as shown in Figures 2 and 3. When used with a 5V regulator, a 16V 10μF Y5V capacitor can exhibit an effective value as low as 1μF to 2μF for the DC bias voltage applied and over the operating tempera- ture range. The X5R and X7R dielectrics result in more stable characteristics and are more suitable for use as the output capacitor. The X7R type has better stability across temperature, while the X5R is less expensive and is avail- able in higher values. Care still must be exercised when using X5R and X7R capacitors; the X5R and X7R codes only specify operating temperature range and maximum capacitance change over temperature. Capacitance change due to DC bias with X5R and X7R capacitors is better than Y5V and Z5U capacitors, but can still be significant enough to drop capacitor values below appropriate levels. Capaci- tor DC bias characteristics tend to improve as component case size increases, but expected capacitance at operating voltage should be verified. Figure 2. Ceramic Capacitor DC Bias Characteristics Figure 3. Ceramic Capacitor Temperature Characteristics VIN 3012 F01 VOUT R2 R1 + R2 R1 VOUT = 1.24V VADJ = 1.24V IADJ = 30nA AT 25°C OUTPUT RANGE = 1.24V TO 60V + (IADJ)(R2) 1 + IN LT3012 OUT ADJ GND DC BIAS VOLTAGE (V) 3012 F02 20 0 –20 –40 –60 –80 –100 0 4 8 10 26 12 14 X5R Y5V 16 BOTH CAPACITORS ARE 16V, 1210 CASE SIZE, 10μF TEMPERATURE (°C) –50 40 20 0 –20 –40 –60 –80 –100 25 75 3012 F03 –25 0 50 100 125 Y5V X5R BOTH CAPACITORS ARE 16V, 1210 CASE SIZE, 10μF |
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