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AN1283 Datasheet(PDF) 7 Page - STMicroelectronics |
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AN1283 Datasheet(HTML) 7 Page - STMicroelectronics |
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7 / 7 page  AN1283 - APPLICATION NOTE 7/7 Information furnished is believed to be accurate and reliable. However, STMicroelectronics assumes no responsibility for the consequences of use of such information nor for any infringement of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of STMicroelectronics. Specifications mentioned in this publication are subject to change without notice. This publication supersedes and replaces all information previously supplied. STMicroelectronics products are not authorized for use as critical components in life support devices or systems without express written approval of STMicroelectronics. © The ST logo is a registered trademark of STMicroelectronics © 2001 STMicroelectronics - Printed in Italy - All Rights Reserved STMicroelectronics GROUP OF COMPANIES Australia - Brazil - China - Finland - France - Germany - Hong Kong - India - Italy - Japan - Malaysia - Malta - Morocco Singapore - Spain - Sweden - Switzerland - United Kingdom © http://www.st.com For medium currents (< 1A), a good value for the voltage drop through R5 can be Vsense = 200mV (dissipation < 200mW). The resistor bridge R2/R3 should be chosen following equation 2 : u V sense = R3 / (R2+R3) x Vref eq2 The total value of the resistor bridge should be in the range of the kW in order to ensure a proper charge for the voltage reference (in the range of the mA). To set the current limit, the sense resistor R5 should be chosen following equation 3 : u I lim = Vsense / R5 eq3 The internal current generator (Isce) can be used to offset the current limitation with a lower value. This current generator is activated by connecting pin 2 to ground. It is inhibited if pin 2 is connected to the positive rail via the pull up resistor R1. The current offset is given by the choice of the resistor R4. If Ilim1 is the current limit calculated in the previous paragraph, and Ilim2 is the current limit that is to be set when pin 2 is connected to ground, R4 should be chosen following equation 4 : u R 4 = (Vsense - Ilim2 x R5) / Isce eq4 where Isce = 1.4mA C4 and C5 are bypass capacitors used to smoothen the regulated outputs. C2 and C3 are capacitors used for high frequency compensation. EXAMPLES OF COMPONENT LISTS Table 1 summarizes a few examples of component lists to generate quickly 15V/700mA/ 200mA, 12V/1A/500mA or 8.2V/200mA/100mA voltage and current regulations. Table 1 Figure 8 Voltage/ Current Control 15V 700mA 200mA 12V 1A 500mA 8.2V 200mA 100mA R1 10k Ω 10k Ω 10k Ω R2 1.2k Ω 1.2k Ω 1.2k Ω R3 220 Ω 220 Ω 220 Ω R4 100 Ω 68 Ω 68 Ω R5 1.2 Ωx4 0.8 Ωx4 1 Ωx4 R6 1k Ω 1k Ω 1k Ω R7 12k Ω 8.2k Ω 5.6k Ω P1 100 Ω 100 Ω 100 Ω 2 straps 0 Ω 0 Ω 0 Ω C2 100nF 100nF 100nF C3 100nF 100nF 100nF C4 10 µF22µF 4.7 µF C5 100nF 100nF 100nF |
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Similar Description - AN1283 |
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