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NCP1086 Datasheet(PDF) 7 Page - ON Semiconductor |
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NCP1086 Datasheet(HTML) 7 Page - ON Semiconductor |
7 / 14 page NCP1086 http://onsemi.com 7 Protection Diodes When large external capacitors are used with a linear regulator it is sometimes necessary to add protection diodes. If the input voltage of the regulator gets shorted, the output capacitor will discharge into the output of the regulator. The discharge current depends on the value of the capacitor, the output voltage and the rate at which VIN drops. In the NCP1086 series linear regulator, the discharge path is through a large junction and protection diodes are not usually needed. If the regulator is used with large values of output capacitance and the input voltage is instantaneously shorted to ground, damage can occur. In this case, a diode connected as shown in Figure 17 or Figure 18 is recommended. Figure 17. Protection Diode Scheme for Large Output Capacitors (Adjustable Output) C2 VOUT VIN C1 VIN VOUT Adj NCP1086 IN4002 (optional) R1 R2 Figure 18. Protection Diode Scheme for Large Output Capacitors (3.3 V Fixed Output) C2 VOUT VIN C1 VIN VOUT GND NCP1086 IN4002 (optional) Output Voltage Sensing Since the NCP1086 is a three terminal regulator, it is not possible to provide true remote load sensing. Load regulation is limited by the resistance of the conductors connecting the regulator to the load. For best results the fixed output regulator should be connected as shown in Figure 19. Figure 19. Conductor Parasitic Resistance Effects Can Be Minimized with the Above Grounding Scheme for Fixed Output Regulators VIN VIN VOUT NCP1086 Conductor Parasitic Resistance RLOAD RC For the adjustable regulator, the best load regulation occurs when R1 is connected directly to the output pin of the regulator as shown in Figure 20. If R1 is connected to the load, RC is multiplied by the divider ratio and the effective resistance between the regulator and the load becomes RC R1 ) R2 R1 where RC = conductor parasitic resistance. Figure 20. Grounding Scheme for the Adjustable Output Regulator to Minimize Parasitic Resistance Effects VIN VIN VOUT Adj NCP1086 Conductor Parasitic Resistance R1 RLOAD R2 RC Calculating Power Dissipation and Heatsink Requirements The NCP1086 linear regulator includes thermal shutdown and current limit circuitry to protect the device. High power regulators such as these usually operate at high junction temperatures so it is important to calculate the power dissipation and junction temperatures accurately to ensure that an adequate heatsink is used. |
Similar Part No. - NCP1086_05 |
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Similar Description - NCP1086_05 |
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