LM3481MMX National Semiconductor, LM3481MMX Datasheet

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... Power saving shutdown mode reduces the total supply current to 5µA and allows power supply sequencing. Internal soft-start limits the inrush current at start-up. Typical Application Circuit © 2007 National Semiconductor Corporation Key Specifications ■ Wide supply voltage range of 2.97V to 48V ■ ...

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... Connection Diagram Package Marking and Ordering Information Order Number LM3481MM LM3481MMX Pin Description Pin Name Pin Number I SEN UVLO COMP FB AGND FA/SYNC/SD PGND www.national.com 10-Lead Mini SOIC Package (MSOP-10 Package) Package Type Package Marking MSOP-10 SJPB MSOP-10 SJPB Description 1 Current sense input pin ...

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... Absolute Maximum Ratings If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. V pin Voltage IN FB Pin Voltage FA/SYNC/SD Pin Voltage COMP Pin Voltage UVLO Pin Voltage V Pin Voltage CC DR Pin Voltage I Pin Voltage ...

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Symbol Parameter Current Sense Threshold V SENSE Voltage Over Load Current Limit V SC Sense Voltage Internal Compensation V SL Ramp Voltage Output Over-voltage V Protection (with respect to OVP feedback voltage) (Note 7) Output Over-Voltage V OVP(HYS) Protection Hysteresis ...

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Note 1: Absolute Maximum Ratings are limits beyond which damage to the device may occur. Operating Ratings indicates conditions for which the device is intended to be functional, but does not guarantee specific performance limits. For guaranteed specifications and test ...

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Efficiency vs. Load Current (9V COMP Pin Source Current vs. Temperature I vs. Input Voltage (Switching) Supply www.national.com and 12V ) IN OUT 20136550 I Supply 20136552 Shutdown Threshold Hysteresis vs. Temperature 20136554 6 Frequency vs. Temperature 201365a7 vs. Input ...

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Drive Voltage vs. Input Voltage Current Sense Threshold vs. Input Voltage Minimum On-Time vs. Temperature Short Circuit Protection vs. V 20136557 Compensation Ramp Amplitude vs. Input Voltage 20136559 201365a8 7 IN 20136558 20136560 www.national.com ...

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Functional Block Diagram Functional Description The LM3481 uses a fixed frequency, Pulse Width Modulated (PWM), current mode control architecture typical appli- cation circuit, the peak current through the external MOSFET is sensed through an external sense resistor. The ...

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FIGURE 1. Basic Operation of the PWM comparator OVER VOLTAGE PROTECTION The LM3481 has over voltage protection (OVP) for the output voltage. OVP is sensed at the feedback pin (FB anytime the voltage at the feedback pin rises ...

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FIGURE 3. Compensation Ramp Avoids Sub-Harmonic Oscillation To prevent the sub-harmonic oscillations, a compensation ramp is added to the control signal, as shown in Figure 3. With the compensation ramp, ΔV samp1 criteria are expressed by, The compensation ramp has ...

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It is good design practice to only add as much slope com- pensation as needed to avoid subharmonic oscillation. Addi- tional slope compensation minimizes the influence of the sensed current in the control loop. With very large slope com- pensation ...

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FIGURE 9. Shutdown Operation in Frequency Adjust Mode FIGURE 10. Shutdown Operation in Synchronization Mode www.national.com FIGURE 7. Frequency Adjust FIGURE 8. Frequency Synchronization 12 20136514 20136515 20136516 20136517 ...

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Under Voltage Lockout (UVLO) Pin The UVLO pin provides user programmable enable and shut- down thresholds. The UVLO pin is compared to an internal reference of 1.43V (typical), and a resistor divider programs . When the IC is enabled, a ...

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FIGURE 12. Simplified Boost Converter Diagram (a) First cycle of operation. (b) Second cycle of operation POWER INDUCTOR SELECTION The inductor is one of the two energy storage elements in a boost converter. Figure 13 shows how the inductor current ...

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PROGRAMMING THE OUTPUT VOLTAGE AND OUTPUT CURRENT The output voltage can be programmed using a resistor di- vider between the output and the feedback pins, as shown in Figure 14. The resistors are selected such that the voltage at the ...

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POWER MOSFET SELECTION The drive pin, DR, of the LM3481 must be connected to the gate of an external MOSFET boost topology, the drain of the external N-Channel MOSFET is connected to the in- ductor and the source ...

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The most important layout rule is to keep the AC current loops as small as possible. Figure 16 shows the current flow of a boost converter. The top schematic shows a dotted line which represents the current flow during on-state ...

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Designing SEPIC Using LM3481 Since the LM3481 controls a low-side N-Channel MOSFET, it can also be used in SEPIC (Single Ended Primary Induc- tance Converter) applications. An example of SEPIC using the LM3481 is shown in Figure 17. As shown ...

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SELECTION OF INDUCTORS L1 AND L2 Proper selection of the inductors L1 and L2 to maintain con- stant current mode requires calculations of the following pa- rameters. Average current in the inductors L2AVE OUT Peak to peak ...

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Input Capacitor Selection Similar to a boost converter, the SEPIC has an inductor at the input. Hence, the input current waveform is continuous and triangular. The inductor ensures that the input capacitor sees fairly low ripple currents. However, as the ...

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Physical Dimensions inches (millimeters) unless otherwise noted 10-Lead MSOP Package NS Package Number MUB10A 21 www.national.com ...

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