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BD4275FP2-C Datasheet(PDF) 12 Page - Rohm |
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BD4275FP2-C Datasheet(HTML) 12 Page - Rohm |
12 / 23 page ![]() 12/20 29.Nov.2013 Rev.003 www.rohm.com © 2013 ROHM Co., Ltd. All rights reserved. TSZ22111・15・001 BD4275FP2-C BD4275FPJ-C Datasheet TSZ02201-0T2T0AN00110-1-2 Thermal Design Refer to the heat mitigation characteristics illustrated in Figure 21, 22 and the power dissipation under actual operating conditions should be taken into consideration and a sufficient margin should be allowed for in the thermal design. The amount of heat generated depends on the voltage difference across the input and output, load current, and bias current. Therefore, when actually using the chip, ensure that the generated heat does not exceed the Pd rating. Even if the ambient temperature Ta is at 25 °C, it is possible that the junction temperature Tj reaches high temperatures. Keep the whole operating temperature range within Tj ≤ Tjmax. Should by any chance the power dissipation rating be exceeded the rise in temperature of the chip may result in deterioration of the properties of the chip. The absolute maximum rating of the Pd stated in this specification is when the IC is mounted on a 114.3mm × 76.2mm × 1.6mmt glass epoxy board. In case of exceeding this absolute maximum rating, increase the board size and copper area to prevent exceeding the Pd rating. The following method is used to calculate the power consumption Pc (W) Pc = ( VCC - VO ) × IO + VCC × ICC Power dissipation Pd ≥ Pc The load current IO is obtained by operating the IC within the power dissipation range. (Refer to Figure 10 for the ICC.) Thus, the maximum load current IOmax for the applied voltage VCC can be calculated during the thermal design process. The following method is also used to calculate the junction temperature Tj. ■TO263-5F ・Calculation example : with TO263-5F package , Ta = 105 °C, VCC = 13.5 V, VO = 5.0 V, board ③ (Figure 21.) At Ta = 105 °C with Figure 21 ③ condition, the calculation shows that 211 mA of output current is possible at 8.5 V potential difference across input and output. ・Calculation example : with Tc (bottom) = 80 °C, VCC = 13.5 V, VO = 5.0 V, IO = 200 mA, board ③ (Figure 21.) Pc of the IC can be calculated as follows: Pc = ( VCC - VO ) × IO + VCC × ICC Pc = ( 13.5 V - 5.0 V ) × 200 mA + 13.5 V × ICC Pc = 1.7 W ( ICC = 80 µA ) In case the power consumption Pc is 1.7 W, the junction temperature Tj can be calculated as follows: Tj = Pc × θjc + Tc Tj = 1.7 W × θjc + 80 °C Tj = 81.7 °C ( θjc (bottom) = 1 °C / W Refer to Page 4 Thermal Design) The junction temperature is 81.7 °C, at above condition. VCC : Input Voltage Ta : Ambient Temperature VO : Output Voltage Tc : Case Temperature IO : Load Current, Tj : Junction Temperature ICC : Circuit Current θjc : Thermal Resistance (Junction to Case (bottom)) Pc : Power Consumption IO ≤ Pd - VCC × ICC VCC - VO IO ≤ 1.8 W – 13.5 V × 80 µA 13.5 V – 5 V ( ICC = 80 µA ) Tj = Pc × θjc + Tc 211 mA IO ≤ Pd at over 25 °C is calculated by below. Pd = (Pd at 25 °C) × (150 - Ta) / (150 - 25) In case of board③ in Figure 21, Ta = 105 °C Pd = 1.8 W |
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