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LTM4676A Arkusz danych(PDF) 67 Page - Linear Technology |
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LTM4676A Arkusz danych(HTML) 67 Page - Linear Technology |
67 / 136 page LTM4676A 67 4676afa For more information www.linear.com/LTM4676A applicaTions inForMaTion on DC1811B-B hardware; a 4-layer FR4 PCB measuring 99mm × 133mm × 1.6mm using outer and inner copper weights of 2oz and 1oz, respectively. The power loss curves are taken at room temperature, and are increased with multiplicative factors with ambient temperature. These approximate factors are listed in Table 14. (Compute the factor by interpolation, for intermediate temperatures.) The derating curves are plotted with the LTM4676A’sparalleledoutputsinitiallysourcingupto26A and the ambient temperature at 30°C. The output voltages are 1V, 1.8V and 3.3V. These are chosen to include the lower and higher output voltage ranges for correlating the thermal resistance. Thermal models are derived from several temperature measurements in a controlled temperature chamber along with thermal modeling analysis. The junction temperatures are monitored while ambient temperature is increased with and without air flow, and with and without a heat sink attached with thermally conductive adhesive tape. The BGA heat sinks evaluated in Table 18 (and attached to the LTM4676A with thermally conductive adhesive tape listed in Table 19) yield very comparable performance in laminar airflow despite being visibly different in construction and form factor. The power loss increase with ambient temperature change is factored into the derating curves. The junctions are maintained at 120°C maximum while lowering output current or power while increasing ambient temperature. The decreased output current decreases the internal module loss as ambient temperature is increased. The monitored junction temperature of 120°C minus the ambientoperatingtemperaturespecifieshowmuchmodule temperaturerisecanbeallowed.AsanexampleinFigure 15, the load current is derated to ~19A at ~80°C ambient with 400LFM airflow and no heat sink and the room temperature (25°C) power loss for this 12VIN to 1VOUT at 19AOUT condition is ~4W. A 4.8W loss is calculated by multiplyingthe~4Wroomtemperaturelossfromthe12VIN to 1VOUT power loss curve at 19A (Figure 11), with the 1.2 multiplying factor at 80°C ambient (from Table 14). If the 80°C ambient temperature is subtracted from the 120°C junction temperature, then the difference of 40°C divided by 4.8W yields a thermal resistance, θJA, of 8.3°C/W—in good agreement with Table 15. Table 15, Table 16 and Table17provideequivalentthermalresistancesfor1V,1.8V and3.3Voutputswithandwithoutairflowandheatsinking. The derived thermal resistances in Table 15, Table 16 and Table 17 for the various conditions can be multiplied by the calculated power loss as a function of ambient temperature to derive temperature rise above ambient, thus maximum junction temperature. Room temperature power loss can be derived from the efficiency curves in the Typical Performance Characteristics section and adjusted with ambient temperature multiplicative factors from Table 14. Table 14. Power Loss Multiplicative Factors vs Ambient Temperature AMBIENT TEMPERATURE POWER LOSS MULTIPLICATIVE FACTOR Up to 40°C 1.00 50°C 1.05 60°C 1.10 70°C 1.15 80°C 1.20 90°C 1.25 100°C 1.30 110°C 1.35 120°C 1.40 |
Podobny numer części - LTM4676A |
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Podobny opis - LTM4676A |
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