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STP1117S25 Scheda tecnica(PDF) 6 Page - SeCoS Halbleitertechnologie GmbH |
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STP1117S25 Scheda tecnica(HTML) 6 Page - SeCoS Halbleitertechnologie GmbH |
6 / 6 page Elektronische Bauelemente STP1117Sxx Series 1.0A Low Dropout Positive Adjustable or Fixed-Mode Regulator 27-Jun-2017 Rev. B Page 6 of 6 http://www.SeCoSGmbH.com/ Any changes of specification will not be informed individually. APPLICATION INFORMATION Output Voltage The STP1117S develops a 1.25V reference Voltage Between the output and the adjust terminal. By placing A resistor between these two terminals, a constant current Is cause to flow through R1 and down through R2 to set the Overall output voltage. Normally, this current is chosen to be the specified minimum load current of 10mA . For fixed voltage devices R1 and R2 are included in the device. 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 data sheet specification foe load regulation is measured at the output pin of the device. Best load regulation is obtained when the top of the resistor divider (R1) is tied directly to the output pin of the device not 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, RP is multiplied by the divider ratio, the effective resistance between the regulator and the load would be: RP × (1 + R2/R1), RP = Parasitic Line Resistance Input Capacitor An input capacitor of 10µF 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 STP1117S requires an output capacitor to maintain stability and improve transient response. Proper capacitor selection is important to ensure proper operation. The STP1117S output capacitor selection is dependent upon the ESR (equivalent series resistance) of the output capacitor to maintain stability. When the output capacitor is 10µF or greater, the output capacitor should have an ESR less than 1 . This will improve transient response as well as promote stability. A low-ESR solid tantalum capacitor works extremely well and provides good transient response and stability over temperature. Aluminum electrolytics can also be used, as long as the ESR of the capacitor is <1 . 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 using an adjustable device with the adjust pin bypassed. With a 25µF bypassing capacitor, 75dB ripple rejection is obtainable at any output level. The impedance of the adjust pin capacitor, at the ripple frequency, should be <R1. R1 is normally in the range of 100W to 200W. The size of the required adjust pin capacitor is the function of the input ripple frequency. At 120Hz, with R1=100 ,the adjust pin capacitor should be 13µF. For fixed voltage devices and adjustable devices without an adjust pin capacitor, the output ripple will increase as the ratio of the output voltage to the reference voltage (VOUT /VREF). |
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