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SPX1587AT Datasheet(PDF) 4 Page - Sipex Corporation |
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SPX1587AT Datasheet(HTML) 4 Page - Sipex Corporation |
4 / 11 page Jun8-07 Rev D SPX587 Low-Dropout Voltage Regulator © 2007 Sipex Corporation APPLICATION INFORMATION Output Capacitor To ensure the stability of the SPX1587, an output capacitor of at least 10µF (ceramic or tantalum) or 22µF (aluminum) is required. The value may change based on the application requirements of the output load or temperature range. The value of ESR can vary based on the type of capacitor used in the applica- tions to guarantee stability. The recommended value for ESR is 0.5 or less. A larger value of output capacitance (up to 100µF) can improve the load transient response. Soldering Methods The SPX1587 die is attached to the heatsink lead which exits opposite the input, output, and ground pins. Thermal Characteristics The SPX1587 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 tempera- ture does not exceed 125°C. Thermal protection is activated at >179°C and deactiviated at <165 °C. The thermal interaction from other components in the application can effect the thermal resistance of the SPX1587. The actual thermal resistance can be determined with experimentation. SPX1587 power dissipation is calculated as follows: P D= (V IN- V OUT)(IOUT) Maximum Junction Temperature range: T J= T A(max) + PD* JA (junction-to-ambient thermal resistance) Maximumjunctiontemperaturemustnotexceed125°C. Ripple Rejection Ripple rejection can be improved by adding a capaci- tor between the ADJ pin and ground as shown in Figure 8. When ADJ pin bypassing is used, the value of the output capacitor required increases to its maxi- mum. If the ADJ pin is not bypassed, the value of the output capacitor can be lowered to 22µF for an electrolytic aluminum capacitor or 10µF for a solid tantalum capacitor (Fig 7). However the value of the ADJ-bypass capacitor should be chosen with respect to the following equation: C = 1 / ( 6.28 * F R* R 1) 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 amplitude 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 5. Output Voltage The output of the adjustable regulator can be set to any voltage between 1.25V and 15V. The value of V OUT can be quickly approximated using the formula V OUT=1.25 *(R1+ R 2)/R1 A small correction to this formula is required de- pending on the values of resistors R 1 and R2, since the adjustable pin current (approx 50µA) flows through R 2. When I ADJ is taken into account, the formula becomes V OUT= V REF(1+ (R2/R1)) + IADJ* R 2 where V REF=1.25V Layout Considerations Parasitic line resistance can degrade load regulation. In order to avoid this, connect R 1 directly to VOUT as illustrated in Figure 13. For the same reason, R 2 should be connected to the negative side of the load. |
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