Datasheet LT3014B (Analog Devices) - 9

LT3014B
APPLICATIONS INFORMATION
40 The GND pin current can be found by examining the GND Pin Current curves in the Typical Performance Character- 20 istics. Power dissipation will be equal to the sum of the 0 two components listed above. X5R –20 The LT3014B regulator has internal thermal limiting de- –40 signed to protect the device during overload conditions. Y5V For continuous normal conditions the maximum junction –60 CHANGE IN VALUE (%) temperature rating of 125°C must not be exceeded. It is –80 BOTH CAPACITORS ARE 16V, important to give careful consideration to all sources of 1210 CASE SIZE, 10µF –100 thermal resistance from junction to ambient. Additional –50 –25 0 25 50 75 100 125 TEMPERATURE (°C) heat sources mounted nearby must also be considered. 3014B F03 For surface mount devices, heat sinking is accomplished
Figure 3. Ceramic Capacitor Temperature Characteristics
by using the heat spreading capabilities of the PC board and its copper traces. Copper board stiffeners and plated able in higher values. Care still must be exercised when through-holes can also be used to spread the heat gener- using X5R and X7R capacitors; the X5R and X7R codes ated by power devices. only specify operating temperature range and maximum capacitance change over temperature. Capacitance change The following table lists thermal resistance for several due to DC bias with X5R and X7R capacitors is better than different board sizes and copper areas. All measurements Y5V and Z5U capacitors, but can still be significant enough were taken in still air on 3/32” FR-4 board with one ounce to drop capacitor values below appropriate levels. Capaci- copper. tor DC bias characteristics tend to improve as component
Table 1. SOT-23 Measured Thermal Resistance
case size increases, but expected capacitance at operating
COPPER AREA
voltage should be verified.
THERMAL RESISTANCE TOPSIDE BACKSIDE BOARD AREA (JUNCTION-TO-AMBIENT)
Voltage and temperature coefficients are not the only 2500 sq mm 2500 sq mm 2500 sq mm 125°C/W sources of problems. Some ceramic capacitors have a 1000 sq mm 2500 sq mm 2500 sq mm 125°C/W piezoelectric response. A piezoelectric device generates 225 sq mm 2500 sq mm 2500 sq mm 130°C/W voltage across its terminals due to mechanical stress, 100 sq mm 2500 sq mm 2500 sq mm 135°C/W similar to the way a piezoelectric accelerometer or micro- 50 sq mm 2500 sq mm 2500 sq mm 150°C/W phone works. For a ceramic capacitor the stress can be induced by vibrations in the system or thermal transients.
Table 2. DFN Measured Thermal Resistance Thermal Considerations COPPER AREA THERMAL RESISTANCE TOPSIDE BACKSIDE BOARD AREA (JUNCTION-TO-AMBIENT)
The power handling capability of the device will be limited 2500 sq mm 2500 sq mm 2500 sq mm 40°C/W by the maximum rated junction temperature (125°C). The 1000 sq mm 2500 sq mm 2500 sq mm 45°C/W power dissipated by the device will be made up of two 225 sq mm 2500 sq mm 2500 sq mm 50°C/W components: 100 sq mm 2500 sq mm 2500 sq mm 62°C/W 1. Output current multiplied by the input/output voltage For the DFN package, the thermal resistance junction-to- differential: IOUT • (VIN – VOUT) and, case (θJC), measured at the Exposed Pad on the back of 2. GND pin current multiplied by the input voltage: the die, is 16°C/W. IGND • VIN. 3014bfb For more information www.linear.com/LT3014B 9 Document Outline Features Description Applications Typical Application Absolute Maximum Ratings Pin Configuration Electrical Characteristics Typical Performance Characteristics Pin Functions Applications Information