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LT3021ES8-1.2 Datasheet(PDF) 11 Page - Linear Technology |
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LT3021ES8-1.2 Datasheet(HTML) 11 Page - Linear Technology |
11 / 16 page 11 LT3021/LT3021-1.2/ LT3021-1.5/LT3021-1.8 3021fa The LT3021 regulator has internal thermal limiting (with hysteresis) designed to protect the device during overload conditions. For normal continuous conditions, do not exceed the maximum junction temperature rating of 125 °C. Carefully consider all sources of thermal resistance from junction to ambient including other heat sources mounted in proximity to the LT3021. The underside of the LT3021 DH package has exposed metal (14mm2) from the lead frame to where the die is attached. This allows heat to directly transfer from the die junction to the printed circuit board metal to control maximum operating junction temperature. The dual-in-line pin ar- rangement allows metal to extend beyond the ends of the package on the topside (component side) of a PCB. Con- nect this metal to GND on the PCB. The multiple IN and OUT pins of the LT3021 also assist in spreading heat to the PCB. The LT3021 S8 package has pin 4 fused with the lead frame. This also allows heat to transfer from the die to the printed circuit board metal, therefore reducing the thermal resistance. Copper board stiffeners and plated through- holes can also be used to spread the heat generated by power devices. The following tables list thermal resistance for several different board sizes and copper areas for two different packages. Measurements were taken in still air on 3/32" FR-4 board with one ounce copper. Table 1. Measured Thermal Resistance For DH Package COPPER AREA THERMAL RESISTANCE TOPSIDE* BACKSIDE BOARD AREA (JUNCTION-TO-AMBIENT) 2500mm 2 2500mm 2 2500mm 2 30 °C/W 900mm 2 2500mm 2 2500mm 2 35 °C/W 225mm 2 2500mm 2 2500mm 2 50 °C/W 100mm 2 2500mm 2 2500mm 2 55 °C/W 50mm 2 2500mm 2 2500mm 2 65 °C/W Table 2. Measured Thermal Resistance For S8 Package COPPER AREA THERMAL RESISTANCE TOPSIDE* BACKSIDE BOARD AREA (JUNCTION-TO-AMBIENT) 2500mm 2 2500mm 2 2500mm 2 70 °C/W 1000mm 2 2500mm 2 2500mm 2 70 °C/W 225mm 2 2500mm 2 2500mm 2 78 °C/W 100mm 2 2500mm 2 2500mm 2 84 °C/W 50mm 2 2500mm 2 2500mm 2 96 °C/W *Device is mounted on topside. Calculating Junction Temperature Example: Given an output voltage of 1.2V, an input voltage range of 1.8V ±10%, an output current range of 1mA to 500mA, and a maximum ambient temperature of 70 °C, what will the maximum junction temperature be for an application using the DH package? The power dissipated by the device is equal to: IOUT(MAX)(VIN(MAX) – VOUT) + IGND(VIN(MAX)) where IOUT(MAX) = 500mA VIN(MAX) = 1.98V IGND at (IOUT = 500mA, VIN = 1.98V) = 10mA so P = 500mA(1.98V – 1.2V) + 10mA(1.98V) = 0.41W The thermal resistance is in the range of 35 °C/W to 70 °C/W depending on the copper area. So the junction temperature rise above ambient is approximately equal to: 0.41W(52.5 °C/W) = 21.5°C The maximum junction temperature equals the maximum junction temperature rise above ambient plus the maxi- mum ambient temperature or: TJMAX = 21.5°C + 70°C = 91.5°C Protection Features The LT3021 incorporates several protection features that make it ideal for use in battery-powered circuits. In addi- tion to the normal protection features associated with monolithic regulators, such as current limiting and ther- mal limiting, the device also protects against reverse- input voltages, reverse-output voltages and reverse output-to-input voltages. Current limit protection and thermal overload protection protect the device against current overload conditions at the output of the device. For normal operation, do not exceed a junction temperature of 125 °C. The IN pins of the device withstand reverse voltages of 10V. The LT3021 limits current flow to less than 1 µA and no negative voltage appears at OUT. The device protects both itself and the load against batteries that are plugged in backwards. APPLICATIO S I FOR ATIO |
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