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APL1117A15UEE-TRG Datasheet(PDF) 6 Page - Anpec Electronics Coropration |
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APL1117A15UEE-TRG Datasheet(HTML) 6 Page - Anpec Electronics Coropration |
6 / 13 page Copyright © ANPEC Electronics Corp. Rev. A.4 - May., 2010 APL1117A www.anpec.com.tw 6 Application Information Output Voltage The output voltage of the APL1117A-ADJ can be adjusted with a resistive divider from output voltage to ADJ pin to ground (see Figure1), and the internal reference voltage is 1.25V. The following equation can be used to calculate the output voltage: Figure 1. Basic Adjustable Regulator Load Regulation When the adjustable regulator is used, load regulation will be limited by the resistance of the wire connecting the regulator to the load. The datasheet specification for load regulation is measured at the output pin of the device. The best load regulation is obtained when the top of the resistor divider (R1) is tied directly to the output pin of the device, but to the load. For fixed voltage devices, the top of R1 is internally connected to the output, and the ground pin can be connected to low side of the load. If R1 is connected to the load, R P is multiplied by the divider ratio, the effective resistance between the regulator and the load would be: Figure 2. Connections for The Best Load Regulation Input Capacitor An input capacitor of 10 µF or greater is recommended. Tantalum or aluminum electrolytic capacitors can be used for bypassing. Larger Values will improve ripple rejection by bypassing the input to the regulator. Output Capacitor The APL1117A requires an output capacitor to maintain stability and improve transient response. Proper capaci- tor selection is important to ensure proper operation. The APL1117A output capacitor selection depends upon the ESR (equivalent series resistance) of the output capaci- tor to maintain stability. When the output capacitor is 10 µF or greater, the output capacitor should have an ESR be- tween 0.15 Ω to 20Ω. This will improve transient response as well as promote stability. A low-ESR solid tantalum capacitor works extremely well and provides good tran- sient response and stability over temperature. Aluminum electrolytics can also be used, as long as the ESR of the capacitor is less than1 Ω. The value of the output capacitor can be increased without limit. Higher capacitance values help to improve transient response and ripple rejection and reduce output noise. Ripple Rejection The curves for Ripple Rejection were generated by using an adjustable device with the adjust pin bypassed. With a 22 µF bypassing capacitor, 60dB ripple rejection is ob- tainable at any output level. The impedance of the adjust pin capacitor, at the ripple frequency, should be < R1. R1 V IN APL1117A OUT IN ADJ R1 R2 Rp PARASITIC LINE RESISTANCE CONNECT R1 TO CASE CONNECT R2 TO LOAD RL Rp X (1+ ), Rp = Parasitic Line Resistance R2 R1 R2 I ) R1 R2 1 ( V 25 . 1 V ADJ OUT × + + × = Where the I ADJ is a constant current flows through R2 and represents a small error. Because the I ADJ is very small, it can usually be ignored. Note that the APL1117A-ADJ needs a minimum load current of 10mA to present the output voltage. For fixed voltage devices, the R1 and R2 are in- cluded in the device. V IN APL1117A VOUT VIN ADJ V REF R1 R2 V OUT I ADJ 60 µA |
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