Datasheet LT3080-1 (Analog Devices) - 10

LT3080-1
applicaTions inFormaTion
temperature and applied voltage. The most common to drop capacitor values below appropriate levels. Capaci- dielectrics used are specified with EIA temperature char- tor DC bias characteristics tend to improve as component acteristic codes of Z5U, Y5V, X5R and X7R. The Z5U and case size increases, but expected capacitance at operating Y5V dielectrics are good for providing high capacitances voltage should be verified. in a small package, but they tend to have strong voltage and temperature coefficients as shown in Figures 2 and 3. Voltage and temperature coefficients are not the only When used with a 5V regulator, a 16V 10µF Y5V capacitor sources of problems. Some ceramic capacitors have a can exhibit an effective value as low as 1µF to 2µF for the piezoelectric response. A piezoelectric device generates DC bias voltage applied and over the operating tempera- voltage across its terminals due to mechanical stress, ture range. The X5R and X7R dielectrics result in more similar to the way a piezoelectric microphone works. For a stable characteristics and are more suitable for use as the ceramic capacitor the stress can be induced by vibrations output capacitor. The X7R type has better stability across in the system or thermal transients. temperature, while the X5R is less expensive and is avail-
Paralleling Devices
able in higher values. Care still must be exercised when using X5R and X7R capacitors; the X5R and X7R codes LT3080-1’s may be directly paralleled to obtain higher only specify operating temperature range and maximum output current. The SET pins are tied together and the capacitance change over temperature. Capacitance change IN pins are tied together. This is the same whether it’s in due to DC bias with X5R and X7R capacitors is better than three terminal mode or has separate input supplies. The Y5V and Z5U capacitors, but can still be significant enough outputs are connected in common; the internal ballast resistor equalizes the currents. 20 BOTH CAPACITORS ARE 16V, 1210 CASE SIZE, 10µF The worst-case offset between the SET pin and the output 0 of only ±2 millivolts allows very small ballast resistors X5R to be used. As shown in Figure 4, the two devices have –20 ALUE (%) internal ballast resistors, which at full output current gives –40 better than 90 percent equalized sharing of the current. –60 The internal resistance of 25 milliohms (per device) only CHANGE IN V Y5V adds about 25 millivolts of output regulation drop at an –80 –100 VIN LT3080-1 0 2 4 6 8 10 12 14 16 DC BIAS VOLTAGE (V) VCONTROL 30801 F02
Figure 2. Ceramic Capacitor DC Bias Characteristics
+ – 25mΩ 40 OUT SET 20 VIN VIN LT3080-1 4.8V TO 28V 0 X5R VCONTROL –20 + –40 1µF Y5V – 25mΩ VOUT OUT –60 CHANGE IN VALUE (%) 3.3V 2.2A SET –80 BOTH CAPACITORS ARE 16V, 10µF 1210 CASE SIZE, 10µF 165k –100–50 –25 0 25 50 75 100 125 30801 F04 TEMPERATURE (°C) 3080 F03
Figure 3. Ceramic Capacitor Temperature Characteristics Figure 4. Parallel Devices
30801fc 10 For more information www.linear.com/LT3080-1 Document Outline Features Applications Typical Application Description Absolute Maximum Ratings Pin Configuration Order Information Electrical Characteristics Typical Performance Characteristics Pin Functions Block Diagram Applications Information Typical Applications Package Description Revision History Typical Application Related Parts