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SPX2920T-5.0 Datasheet(PDF) 4 Page - Sipex Corporation |
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SPX2920T-5.0 Datasheet(HTML) 4 Page - Sipex Corporation |
4 / 10 page 4 Rev:A Date: 03/30/04 SPX2920 400mA Low Drop Out Voltage Regulator with Shutdown ©Copyright 2004 Sipex Corporation UNREGULATED DC 5V @ 400mA MAX TO CMOS OR TTL REFERENCE ERROR DETECTION COMPARATOR ERROR AMPLIFIER 1.23V FROM TTL + + + + + + 60 mV 3 7 8 1 2 6 5 4 Ω .. 60k 330k 180k Ω .. Ω .. 1uF _ _ SPX2920-5.0 Block Diagram External Capacitors The stability of the SPX2920 requires a 2.2 µF or greater capacitor between output and ground. Oscillation could occur without this capacitor. Most types of tantalum or aluminum electrolytic works fine here. For operations of below -25 °C solid tantalum is recommended since the many aluminum types have electrolytes that freeze at about -30 °C. The ESR of about 5Ω or less and resonant frequency above 500kHz are the most important parameters in the value of the capaci- tor. The capacitor value can be increased with- out limit. At lower values of output current, less output capacitance is required for stability. For the currents below 10mA the value of the capacitor can be reduced to 0.5 µF and 0.15µF for 1mA. More output capacitance needed for the 8-pin version at voltages below 5V since it runs the error amplifier at lower gain. At worst case 4.7 µF or greater must be used for the condition of 250mA load at 1.23V output. The SPX2920, unlike other low dropout regu- lators will remain stable and in regulation with no load in addition to the internal voltage di- vider. This feature is especially important in applications like CMOS RAM keep-alive. If there is more than 10 inches of wire between the input and the AC filter capacitor, or if a battery is used as the input, then a 0.1 µF tanta- lum or aluminum electrolytic capacitor should be placed from the input to the ground. Instability can occur if there is stray capaci- tance to the SPX2920 feedback terminal (pin 7). This could cause more problems when using a higher value of external resistors to set the output voltage. This problem can be fixed by adding a 100pF capacitor between output and feedback and increasing the output capacitor to at least 3.3 µF. APPLICATION HINTS BLOCK DIAGRAM |
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