lm3478-mdc National Semiconductor Corporation, lm3478-mdc Datasheet

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... Output current can be programmed with a single external resistor. The LM3478 has built in features such as thermal shutdown, short-circuit protection, over voltage protection, etc. 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 ...

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... Connection Diagram Package Marking and Ordering Information Order Number LM3478MM LM3478MMX Pin Description Pin Name Pin Number I SEN COMP FB AGND PGND DR FA/ www.national.com 10135502 8 Lead Mini SO8 Package (MSOP-8 Package) Package Type Package Marking MSOP-8 S14B MSOP-8 S14B Description 1 Current sense input pin. Voltage generated across an external sense resistor is fed into this 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. Input Voltage FB Pin Voltage FA/SD Pin Voltage < Peak Driver Output Current ( 10µs) Power Dissipation Storage Temperature ...

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Electrical Characteristics Specifications in Standard type face are for T Range. Unless otherwise specified, V Symbol Parameter V Short-Circuit Current SC Limit Sense Voltage V Internal Compensation SL Ramp Voltage V Output Over-voltage OVP Protection (with respect to feedback voltage) ...

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Electrical Characteristics Note 1: Absolute Maximum Ratings are limits beyond which damage to the device may occur. Operating Ratings are conditions under which operation of the device is intended to be functional. For guaranteed specifications and test conditions, see the ...

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Typical Performance Characteristics Frequency vs Temperature Current Sense Threshold vs Input Voltage Efficiency vs Load Current (3.3V In and 12V Out) www.national.com Unless otherwise specified, V Drive Voltage vs Input Voltage 10135554 COMP Pin Voltage vs Load Current 10135545 Efficiency ...

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Typical Performance Characteristics Efficiency vs Load Current (9V In and 12V Out) Error Amplifier Gain COMP Pin Source Current vs Temperature Unless otherwise specified, V Efficiency vs Load Current (3.3V In and 5V Out 10135560 Error Amplifier Phase 10135555 Short ...

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Typical Performance Characteristics Compensation Ramp vs Compensation Resistor Duty Cycle vs Current Sense Voltage www.national.com Unless otherwise specified, V Shutdown Threshold Hysteresis vs Temperature 10135551 10135552 8 = 12V 25˚C. (Continued 10135546 ...

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... Under extremely light load or no-load conditions, the energy delivered to the output capacitor when the external MOSFET is on during the blank-out time is more than what is delivered to the load. An over-voltage comparator inside the LM3478 prevents the output voltage from rising under these condi- tions. The over-voltage comparator senses the feedback (FB pin) voltage and resets the RS latch under these conditions ...

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... Functional Description SLOPE COMPENSATION RAMP The LM3478 uses a current mode control scheme. The main advantages of current mode control are inherent cycle-by- cycle current limit for the switch, and simpler control loop characteristics also easy to parallel power stages using current mode control since current sharing is automatic. ...

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... Functional Description FIGURE 3. Compensation Ramp Avoids Sub-Harmonic Oscillation The compensation ramp has been added internally in LM3478. The slope of this compensation ramp has been selected to satisfy most of the applications. The slope of the internal compensation ramp depends on the frequency. This slope can be calculated using the formula: ...

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... The FA/SD pin also functions as a shutdown pin high signal (refer to the electrical characteristics for definition of high signal) appears on the FA/SD pin, the LM3478 stops www.national.com (Continued) 10135551 FIGURE 5. ∆V ...

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... EMI characteristics than the discontinuous mode. BOOST CONVERTER The most common topology for LM3478 is the boost or step-up topology. The boost converter converts a low input voltage into a higher output voltage. The basic configuration for a boost regulator is shown in Figure 8. In continuous ...

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Typical Applications FIGURE 8. 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 9 shows how the ...

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... A core size with ratings higher than these values should be chosen. If the core is not properly rated, saturation will dramatically reduce overall efficiency. The LM3478 can be set to switch at very high frequencies. When the switching frequency is high, the converter can be operated with very small inductor values. With a small induc- tor value, the peak inductor current can be higher than the output currents, especially under light load conditions ...

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... POWER MOSFET SELECTION The drive pin of LM3478 must be connected to the gate of an external MOSFET boost topology, the drain of the external N-Channel MOSFET is connected to the inductor and the source is connected to the ground. The drive pin + ∆ ...

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... Since the LM3478 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 LM3478 is shown in Figure 12. As shown in Figure 12, the output voltage can be higher or lower than the input voltage. The SEPIC uses two inductors to step-up or step-down the input voltage ...

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... Designing SEPIC Using LM3478 (Continued) The duty cycle of a SEPIC is given by: In the above equation the on-state voltage of the Q MOSFET, Q, and V is the forward voltage drop of the DIODE diode. POWER MOSFET SELECTION As in boost converter, the parameters governing the selec- ...

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... Therefore a good quality capacitor should be chosen in the range of 100µF to 200µ value lower than 100µF is used than problems with impedance interactions or switching noise can affect the LM3478. To improve perfor- mance, especially with V to use a 20Ω resistor at the input to provide a RC filter. The ...

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Output Capacitor Selection (Continued) the output for high efficiency and low ripple voltage. Surface mount tantalums, surface mount polymer electrolytic and polymer tantalum, Sanyo- OSCON, or multi-layer ceramic capacitors are recommended at the output. The output capacitor of the SEPIC ...

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Physical Dimensions inches (millimeters) unless otherwise noted National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and ...