Datasheet LT3023 (Analog Devices) - 10

LT3023
APPLICATIONS INFORMATION Output Capacitance and Transient Response
and temperature coeffi cients as shown in Figures 3 and 4. When used with a 5V regulator, a 16V 10μF Y5V capacitor The LT3023 regulator is designed to be stable with a can exhibit an effective value as low as 1μF to 2μF for the wide range of output capacitors. The ESR of the out- DC bias voltage applied and over the operating tempera- put capacitor affects stability, most notably with small ture range. The X5R and X7R dielectrics result in more capacitors. A minimum output capacitor of 1μF with an stable characteristics and are more suitable for use as the ESR of 3Ω or less is recommended to prevent oscilla- output capacitor. The X7R type has better stability across tions. The LT3023 is a micropower device and output temperature, while the X5R is less expensive and is avail- transient response will be a function of output capacitance. able in higher values. Care still must be exercised when Larger values of output capacitance decrease the peak using X5R and X7R capacitors; the X5R and X7R codes deviations and provide improved transient response for only specify operating temperature range and maximum larger load current changes. Bypass capacitors, used to capacitance change over temperature. Capacitance change decouple individual components powered by the LT3023, due to DC bias with X5R and X7R capacitors is better than will increase the effective output capacitor value. With Y5V and Z5U capacitors, but can still be signifi cant enough larger capacitors used to bypass the reference (for low to drop capacitor values below appropriate levels. Capaci- noise operation), larger values of output capacitors are tor DC bias characteristics tend to improve as component needed. For 100pF of bypass capacitance, 2.2μF of output capacitor is recommended. With a 330pF bypass capacitor 20 or larger, a 3.3μF output capacitor is recommended. The BOTH CAPACITORS ARE 16V, 1210 CASE SIZE, 10μF shaded region of Figure 2 defi nes the region over which 0 the LT3023 regulator is stable. The minimum ESR needed X5R –20 is defi ned by the amount of bypass capacitance used, while the maximum ESR is 3Ω. –40 Extra consideration must be given to the use of ceramic –60 capacitors. Ceramic capacitors are manufactured with a CHANGE IN VALUE (%) Y5V variety of dielectrics, each with different behavior across –80 temperature and applied voltage. The most common –100 dielectrics used are specifi ed with EIA temperature char- 0 2 4 6 8 10 12 14 16 DC BIAS VOLTAGE (V) acteristic codes of Z5U, Y5V, X5R and X7R. The Z5U and 3023 F03 Y5V dielectrics are good for providing high capacitances
Figure 3. Ceramic Capacitor DC Bias Characteristics
in a small package, but they tend to have strong voltage 4.0 40 3.5 20 3.0 0 X5R STABLE REGION 2.5 –20 2.0 ESR (Ω) –40 1.5 CBYP = 0 Y5V CBYP = 100pF –60 1.0 CHANGE IN VALUE (%) CBYP = 330pF CBYP > 3300pF 0.5 –80 BOTH CAPACITORS ARE 16V, 1210 CASE SIZE, 10μF 0 –100 1 2 3 4 5 6 7 8 9 10 –50 –25 0 25 50 75 100 125 OUTPUT CAPACITANCE (μF) TEMPERATURE (°C) 3023 F02 3023 F04
Figure 2. Stability Figure 4. Ceramic Capacitor Temperature Characteristics
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