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Datenblatt-Suchmaschine für elektronische Bauteile |
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Datenblatt-Suchmaschine für elektronische Bauteile |
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CS5205A-1GDPR3 Datenblatt(PDF) 5 Page - Cherry Semiconductor Corporation |
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CS5205A-1GDPR3 Datenblatt(HTML) 5 Page - Cherry Semiconductor Corporation |
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5 / 6 page  5 Best load regulation occurs when R1 is connected directly to the output pin of the regulator as shown in Figure 3. If R1 is connected to the load, RC is multiplied by the divider ratio and the effective resistance between the regulator and the load becomes RC ´ () RC = conductor parasitic resistance Figure 3. Grounding scheme for the adjustable output regulator to min- imize parasitics. The CS5205A-1 linear regulator includes thermal shut- down and safe operating area circuitry to protect the device. High power regulators such as these usually oper- ate at high junction temperatures so it is important to cal- culate the power dissipation and junction temperatures accurately to ensure that an adequate heat sink is used. The case is connected to VOUT on the CS5205A-1, electrical isolation may be required for some applications. Thermal compound should always be used with high current regu- lators such as these. The thermal characteristics of an IC depend on the follow- ing four factors: 1. Maximum Ambient Temperature TA (¡C) 2. Power dissipation PD (Watts) 3. Maximum junction temperature TJ (¡C) 4. Thermal resistance junction to ambient RQJA (C/W) These four are related by the equation TJ = TA + PD ´ RQJA (1) The maximum ambient temperature and the power dissi- pation are determined by the design while the maximum junction temperature and the thermal resistance depend on the manufacturer and the package type. The maximum power dissipation for a regulator is: PD(max)={VIN(max)ÐVOUT(min)}IOUT(max)+VIN(max)IQ (2) where VIN(max) is the maximum input voltage, VOUT(min) is the minimum output voltage, IOUT(max) is the maximum output current, for the application IQ is the maximum quiescent current at IOUT(max). A heat sink effectively increases the surface area of the package to improve the flow of heat away from the IC and into the surrounding air. Each material in the heat flow path between the IC and the outside environment has a thermal resistance. Like series electrical resistances, these resistances are summed to determine RQJA, the total thermal resistance between the junction and the surrounding air. 1. Thermal Resistance of the junction to case, RQJC (¡C/W) 2. Thermal Resistance of the case to Heat Sink, RQCS (¡C/W) 3. Thermal Resistance of the Heat Sink to the ambient air, RQSA (¡C/W) These are connected by the equation: RQJA = RQJC + RQCS + RQSA (3) The value for RQJA is calculated using equation (3) and the result can be substituted in equation (1). The value for RQJC is normally quoted as a single figure for a given package type based on an average die size. For a high current regulator such as the CS5205A-1 the majority of the heat is generated in the power transistor section. The value for RQSA depends on the heat sink type, while RQCS depends on factors such as package type, heat sink interface (is an insulator and thermal grease used?), and the contact area between the heat sink and the package. Once these calculations are complete, the maximum per- missible value of RQJA can be calculated and the proper heat sink selected. For further discussion on heat sink selection, see application note ÒThermal Management for Linear Regulators.Ó Calculating Power Dissipation and Heat Sink Requirements VOUT RC conductor parasitic resistance CS5205A-1 VIN Adj RLOAD R1 R2 R1 + R2 R1 Applications Information: continued |
Ähnliche Teilenummer - CS5205A-1GDPR3 |
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Ähnliche Beschreibung - CS5205A-1GDPR3 |
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