LM3478MM National Semiconductor, LM3478MM Datasheet

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... Typical Application Circuit Typical High Efficiency Step-Up (Boost) Converter © 2005 National Semiconductor Corporation n 10µA shutdown current (over temperature) Features n 8-lead Mini-SO8 (MSOP-8) package n Internal push-pull driver with 1A peak current capability n Current limit and thermal shutdown ...

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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 Range Junction Temperature ESD Susceptibilty ...

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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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Functional Block Diagram Functional Description The LM3478 uses a fixed frequency, Pulse Width Modulated (PWM), current mode control architecture typical appli- cation circuit, the peak current through the external MOS- FET is sensed through an external sense resistor. ...

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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 ...

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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 ...

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Functional Description FIGURE 4. Increasing the Slope of the Compensation Ramp FREQUENCY ADJUST/SHUTDOWN The switching frequency of LM3478 can be adjusted be- tween 100kHz and 1MHz using a single external resistor. This resistor must be connected between FA/SD pin and ...

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Functional Description FIGURE 7. Shutdown Operation in Frequency Adjust Mode SHORT-CIRCUIT PROTECTION When the voltage across the sense resistor (measured on I Pin) exceeds 350mV, short-circuit current limit gets SEN activated. A comparator inside LM3478 reduces the switch- ing frequency ...

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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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Typical Applications (Continued (t) is constant, di (t)/dt must be constant. Hence, for given input voltage and output voltage, the current in the inductor changes at a constant rate. The important quantities in determining a ...

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Typical Applications CURRENT LIMIT WITH ADDITIONAL SLOPE COMPENSATION If an external slope compensation resistor is used (see Figure 4) the internal control signal will be modified and this will have an effect on the current limit. The control signal is ...

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Typical Applications (Continued) where D is the maximum duty cycle. MAX The turn-on and turn-off transitions of a MOSFET require times of tens of nano-seconds. C and Q RSS estimate the large instantaneous power loss that occurs during these transitions. ...

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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 ...

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Designing SEPIC Using LM3478 (Continued) Peak current in the inductor, to ensure the inductor does not saturate: I must be lower than the maximum current rating set by L1PK the current sense resistor. The value of L1 can be increased ...

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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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