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SPX1117S Datasheet(PDF) 7 Page - Sipex Corporation |
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SPX1117S Datasheet(HTML) 7 Page - Sipex Corporation |
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7 / 10 page  7 Date: 8/25/04 SPX1117 800mA Low Dropout Voltage Regulator © Copyright 2004 Sipex Corporation Thermal Characteristics The thermal resistance of SPX1117 (SOT-223 Package) is 15 °C/W from junction to tab and 31 °C/W from tab to ambient for a total of 46 °C/W from junction to ambient (Table 1). The SPX1117 features the internal thermal limiting to protect the device during overload conditions. Special care needs to be taken during continuous load conditions such that the maximum junction tem- perature does not exceed 125 °C. Thermal pro- tection is activated at >155 °C and deactiviated at <140 °C. Taking the FR-4 printed circuit board and 1/16 thick with 1 ounce copper foil as an experiment (fig.13), the PCB material is effective at trans- mitting heat with the tab attached to the pad area and a ground plane layer on the backside of the substrate. Refer to table 1 for the results of the experiment. The thermal interaction from other components in the application can effect the thermal resis- tance of the SPX1117. The actual thermal resistance can be determined with experimenta- tion. SPX1117 power dissipation is calculated as follows: P D = (VIN - VOUT)(IOUT) Maximum Junction Temperature range: T J = TA(max) + PD* thermal resistance (junction-to-ambient) Maximum junction temperature must not ex- ceed the 125 °C. Ripple Rejection Ripple rejection can be improved by adding a capacitor between the ADJ pin and ground as shown in Figure 23. When ADJ pin bypassing is used, the value of the output capacitor re- quired increases to its maximum. If the ADJ pin is not bypassed, the value of the output capacitor can be lowered to 10 µF for an electrolytic alu- minum capacitor or 2.2 µF for a ceramic or solid tantalum capacitor (Fig 22). However the value of the ADJ-bypass capacitor should be chosen with respect to the following equation: C = 1 / ( 6.28 * F R * R1 ) Where C = value of the capacitor in Farads (select an equal or larger standard value), F R = ripple frequency in Hz, R 1 = value of resistor R1 in Ohms. If an ADJ-bypass capacitor is used, the ampli- tude of the output ripple will be independent of the output voltage. If an ADJ-bypass capacitor is not used, the output ripple will be proportional to the ratio of the output voltage to the reference voltage: M = V OUT / VREF Where M = multiplier for the ripple seen when the ADJ pin is optimally bypassed. V REF =1.25V Ripple rejection for the adjustable version is shown in Figure 20. Figure 19. Substrate Layout for SOT-223 50 X 50mm 35 X 17mm 16 X 10mm -90 -80 -70 -60 -50 -40 -30 -20 -10 0 10 100 1000 10000 100000 1000000 Frequency, Hz Figure 20. Ripple Rejection; Vin=3.3V, Vout=1.8V (adj.), Iload=200mA APPLICATION INFORMATION: Continued |
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