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LT3080EDD Datasheet(PDF) 11 Page - Linear Technology |
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LT3080EDD Datasheet(HTML) 11 Page - Linear Technology |
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11 / 26 page  LT3080 11 3080fb (5 milliohms for the two devices in parallel) only adds about 10 millivolts of output regulation drop at an output of 2A. Even with an output voltage as low as 1V, this only adds 1% to the regulation. Of course, more than two LT3080’s can be paralleled for even higher output current. They are spread out on the PC board, spreading the heat. Input resistors can further spread the heat if the input-to-output difference is high. Thermal Performance In this example, two LT3080 3mm × 3mm DFN devices are mounted on a 1oz copper 4-layer PC board. They are placed approximately 1.5 inches apart and the board is mounted vertically for convection cooling. Two tests were set up to measure the cooling performance and current sharing of these devices. The first test was done with approximately 0.7V input- to-output and 1A per device. This gave a 700 milliwatt dissipation in each device and a 2A output current. The temperature rise above ambient is approximately 28°C and both devices were within plus or minus 1°C. Both the thermal and electrical sharing of these devices is excel- lent. The thermograph in Figure 5 shows the temperature distribution between these devices and the PC board reaches ambient temperature within about a half an inch from the devices. The power is then increased with 1.7V across each device. This gives 1.7 watts dissipation in each device and a device temperature of about 90°C, about 65°C above ambient as shown in Figure 6. Again, the temperature matching between the devices is within 2°C, showing excellent tracking between the devices. The board temperature has reached approximately 40°C within about 0.75 inches of each device. While 90°C is an acceptable operating temperature for these devices, this is in 25°C ambient. For higher ambients, the temperature must be controlled to prevent device tempera- ture from exceeding 125°C. A 3-meter-per-second airflow across the devices will decrease the device temperature about 20°C providing a margin for higher operating ambi- ent temperatures. Both at low power and relatively high power levels de- vices can be paralleled for higher output current. Current sharing and thermal sharing is excellent, showing that acceptable operation can be had while keeping the peak temperatures below excessive operating temperatures on a board. This technique allows higher operating current linear regulation to be used in systems where it could never be used before. Quieting the Noise The LT3080 offers numerous advantages when it comes to dealing with noise. There are several sources of noise in a linear regulator. The most critical noise source for any LDO is the reference; from there, the noise contribution Figure 6. Temperature Rise at 1.7W Dissipation Figure 5. Temperature Rise at 700mW Dissipation APPLICATIONS INFORMATION |
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