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REG103UA-3.3 Datasheet(PDF) 11 Page - Texas Instruments |
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REG103UA-3.3 Datasheet(HTML) 11 Page - Texas Instruments |
11 / 26 page REG103 11 SBVS010D FIGURE 11. Maximum Power Dissipation versus Ambient Temperature for the Various Packages and PCB Heat Sink Configurations. 6 5 4 3 2 1 0 0 25 50 75 100 150 125 Ambient Temperature ( °C) CONDITIONS #1 #2 #3 #4 #5 CONDITION PACKAGE PCB AREA JA θ 1 DDPAK 4in2 Top Side Only 27 °C/W 2 SOT-223 4in2 Top Side Only 53 °C/W 3 DDPAK None 65 °C/W 4 SOT-223 0.5in2 Top Side Only 110 °C/W 5 SO-8 None 150 °C/W For large step changes in load current, the REG103 requires a larger voltage drop across it to avoid degraded transient response. The boundary of this “transient drop-out” region is shown as the top line in Figure 10. Values of VIN to VOUT voltage drop above this line insure normal transient response. 250 200 150 100 50 0 0 100 200 300 400 500 I OUT (mA) REG103–3.3 at 25 °C DC Transient FIGURE 10. Transient and DC Dropout. In the transient dropout region between “DC” and “Tran- sient”, transient response recovery time increases. The time required to recover from a load transient is a function of both the magnitude and rate of the step change in load current and the available “headroom” VIN to VOUT voltage drop. Under worst-case conditions (full-scale load change with VIN to VOUT voltage drop close to DC dropout levels), the REG103 can take several hundred microseconds to re-enter the speci- fied window of regulation. TRANSIENT RESPONSE The REG103 response to transient line and load conditions improves at lower output voltages. The addition of a capaci- tor (nominal value 10nF) from the output pin to ground may improve the transient response. In the adjustable version, the addition of a capacitor, CFB (nominal value 10nF), from the output to the adjust pin will also improve the transient response. THERMAL PROTECTION Power dissipated within the REG103 will cause the junction temperature to rise. The REG103 has thermal shutdown circuitry that protects the regulator from damage. The ther- mal protection circuitry disables the output when the junc- tion temperature reaches approximately 150 °C, allowing the device to cool. When the junction temperature cools to approximately 130 °C, the output circuitry is again enabled. Depending on various conditions, the thermal protection circuit may cycle on and off. This limits the dissipation of the regulator, but may have an undesirable effect on the load. Any tendency to activate the thermal protection circuit indicates excessive power dissipation or an inadequate heat sink. For reliable operation, junction temperature should be limited to 125 °C, maximum. To estimate the margin of safety in a complete design (including heat sink), increase the ambient temperature until the thermal protection is triggered. Use worst-case loads and signal conditions. For good reliability, thermal protection should trigger more than 35 °C above the maximum expected ambient condition of your application. This produces a worst-case junction tem- perature of 125 °C at the highest expected ambient tempera- ture and worst-case load. The internal protection circuitry of the REG103 has been designed to protect against overload conditions. It was not intended to replace proper heat sinking. Continuously run- ning the REG103 into thermal shutdown will degrade reli- ability. POWER DISSIPATION The REG103 is available in three different package configu- rations. The ability to remove heat from the die is different for each package type and, therefore, presents different considerations in the printed circuit board (PCB) layout. The PCB area around the device that is free of other components moves the heat from the device to the ambient air. While it is difficult to impossible to quantify all of the variables in a thermal design of this type, performance data for several configurations are shown in Figure 11. In all cases, the PCB copper area is bare copper, free of solder-resist mask, and not solder plated. All examples are for 1-ounce copper. Using heavier copper will increase the effectiveness in moving the heat from the device. In those examples where there is copper on both sides of the PCB, no connection has been provided between the two sides. The addition of plated through holes will improve the heat sink effectiveness. |
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Similar Description - REG103UA-3.3 |
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