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IRU1120 Fiches technique(PDF) 4 Page - International Rectifier |
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IRU1120 Fiches technique(HTML) 4 Page - International Rectifier |
4 / 9 page IRU1120 4 Rev. 1.3 08/20/02 www.irf.com APPLICATION INFORMATION Introduction The IRU1120 adjustable regulator is a five-terminal de- vice designed specifically to provide extremely low drop- out voltages comparable to the PNP type without the disadvantage of the extra power dissipation due to the base current associated with PNP regulators. This is done by bringing out the control pin of the regulator that provides the base current to the power NPN and con- necting it to a voltage that is grater than the voltage present at the VIN pin. This flexibility makes the IRU1120 ideal for applications where dual inputs are available such as a computer mother board with an ATX style power sup- ply that provides 5V and 3.3V to the board. The IRU1120 is specifically designed to meet the fast current transient needs as well as providing an accurate initial voltage, reducing the overall system cost with the need for fewer number of output capacitors. Output Voltage Setting The IRU1120 can be programmed to any voltage in the range of 1.25V to 5.5V by using two external resistors. The output voltage is defined as: Where: VREF = 1.25V Typically IADJ < 1 mA Typically R1 and R2 as shown in Figure 3: Figure 3 - Typical application of the IRU1120 for programming the output voltage. The IRU1120 keeps a constant 1.25V between the ad- just pin and the ground pin. By replacing a resistor (R2), between these two pins, a constant current flows through R1, subtracting the IADJ current out of the R1 to set the overall output voltage. Notice that since the IADJ is typi- cally in the range of 1 mA, it only adds a small error to the output voltage which is negligible. Figure 2 - Simplified block diagram of the IRU1120. BLOCK DIAGRAM VCTRL VIN Gnd 2 1 3 4 VOUT THERMAL SHUTDOWN 1.25V 5 VADJ + + CURRENT LIMIT VOUT R1 R2 VIN VCTRL IADJ = 1uA IRU1120 Adj VOUT VCTRL VIN Gnd VOUT = VREF 3 1+ +IADJ 3R1 R1 R2 ( ) |
Numéro de pièce similaire - IRU1120 |
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Description similaire - IRU1120 |
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