Datasheet LTC3025-1, LTC3025-2, LTC3025-3, LTC3025-4 (Analog Devices) - 10

LTC3025-1/LTC3025-2/ LTC3025-3/LTC3025-4
applicaTions inForMaTion Thermal Considerations
The power dissipated by the device will be equal to: The power handling capability of the device will be limited IOUT(MAX) (VIN(MAX) – VOUT) by the maximum rated junction temperature (125°C). The where: power dissipated by the device will be the output current multiplied by the input/output voltage differential: IOUT(MAX) = 100mA (IOUT) (VIN – VOUT) VIN(MAX) = 3V Note that the BIAS current is less than 500µA even under So: heavy loads, so its power consumption can be ignored P = 100mA(3V – 1.2V) = 0.18W for thermal calculations. Even under worst-case conditions, the LTC3025-X’s BIAS The LTC3025-X has internal thermal limiting designed to pin power dissipation is only about 1mW, thus can be ig- protect the device during momentary overload conditions. nored. Assuming a junction-to-ambient thermal resistance For continuous normal conditions, the maximum junction of 102°C/W, the junction temperature rise above ambient temperature rating of 125°C must not be exceeded. It is will be approximately equal to: important to give careful consideration to all sources of thermal resistance from junction to ambient. Additional 0.18W(102°C/W) = 18.4°C heat sources mounted nearby must also be considered. The maximum junction temperature will then be equal to For surface mount devices, heat sinking is accomplished the maximum junction temperature rise above ambient by using the heat-spreading capabilities of the PC board plus the maximum ambient temperature or: and its copper traces. Copper board stiffeners and plated through holes can also be used to spread the heat gener- TJ = 50°C + 18.4°C = 68.4°C ated by power devices.
Short-Circuit/Thermal Protection
The LTC3025-X 2mm × 2mm DFN package is specified The LTC3025-X has built-in short-circuit current limiting as having a junction-to-ambient thermal resistance of as well as overtemperature protection. During short-circuit 102°C/W, which assumes a minimal heat spreading cop- conditions, internal circuitry automatically limits the output per plane. The actual thermal resistance can be reduced current to approximately 1130mA. At higher temperatures, substantially by connecting the package directly to a good or in cases where internal power dissipation causes exces- heat spreading ground plane. When soldered to 2500mm2 sive self heating on chip, the thermal shutdown circuitry double-sided 1 oz. copper plane, the actual junction-to- will shut down the LDO when the junction temperature ambient thermal resistance can be less than 60°C/W. exceeds approximately 150°C. It will re enable the LDO
Calculating Junction Temperature
once the junction temperature drops back to approximately 140°C. The LTC3025-X will cycle in and out of thermal Example: Given an output voltage of 1.2V, an input voltage shutdown without latch-up or damage until the overstress of 1.8V to 3V, an output current range of 0mA to 100mA condition is removed. Long term overstress (TJ > 125°C) and a maximum ambient temperature of 50°C, what will should be avoided as it can degrade the performance or the maximum junction temperature be? shorten the life of the part. 30251234ff 10 Document Outline Features Description Applications Typical Application Absolute Maximum Ratings Pin Configuration Order Information Electrical Characteristics Typical Performance Characteristics Pin Functions Block Diagram Applications Information Package Description Revision History Typical Application Related Parts