LM3478MA National Semiconductor Corporation, LM3478MA Datasheet
LM3478MA
Available stocks
Related parts for LM3478MA
LM3478MA Summary of contents
Page 1
... Adjustable clock frequency ■ ±2.5% (over temperature) internal reference ■ 10µA shutdown current (over temperature) Typical Application Circuit © 2011 National Semiconductor Corporation LM3478MA Features ■ 8-lead SO–8 package ■ Internal push-pull driver with 1A peak current capability ■ Current limit and thermal shutdown ■ ...
Page 2
... Lead SO–8 Package Package Marking Supplied As: LM3478MA 1000 units on Tape and Reel LM3478MA 2500 units on Tape and Reel Description 1 Current sense input pin. Voltage generated across an external sense resistor is fed into this pin. 2 Compensation pin. A resistor, capacitor combination connected to this pin provides compensation for the control loop ...
Page 3
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 ...
Page 4
Symbol Parameter V Internal Compensation Ramp SL Voltage V ratio SENSE V Output Over-voltage OVP Protection (with respect to feedback voltage) (Note V Output Over-Voltage OVP(HYS) Protection Hysteresis(Note Gm Error Ampifier Transconductance A Error Amplifier Voltage ...
Page 5
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 Electrical Characteristics. ...
Page 6
Typical Performance Characteristics I vs Input Voltage (Shutdown (Switching) Supply IN Frequency vs Temperature www.national.com Unless otherwise specified Input Voltage (Non-Switching) Supply 30150603 Switching Frequency vs R 30150635 Drive Voltage vs Input Voltage ...
Page 7
Current Sense Threshold vs Input Voltage Efficiency vs Load Current (3.3V In and 12V Out) Efficiency vs Load Current (9V In and 12V Out) COMP Pin Voltage vs Load Current 30150645 Efficiency vs Load Current (5V In and 12V Out) ...
Page 8
Error Amplifier Gain COMP Pin Source Current vs Temperature Compensation Ramp vs Compensation Resistor www.national.com Error Amplifier Phase 30150655 Short Circuit Sense Voltage vs Input Voltage 30150636 Shutdown Threshold Hysteresis vs Temperature 30150651 8 30150656 30150657 30150646 ...
Page 9
Duty Cycle vs Current Sense Voltage 30150694 9 www.national.com ...
Page 10
Functional Block Diagram Functional Description The LM3478 uses a fixed frequency, Pulse Width Modulated (PWM) current mode control architecture. The block diagram above shows the basic functionality typical application circuit, the peak current through the external MOSFET is ...
Page 11
Hence, the output voltage overshoot here can also trigger ...
Page 12
Sub-harmonic Oscillation can be easily understood as a ge- ometric problem. If the control signal does not have slope, the slope representing the inductor current ramps up until the control signal is reached and then slopes down again. If the ...
Page 13
FIGURE 6. Frequency Adjust FIGURE 7. Shutdown Operation in Frequency Adjust Mode SHORT-CIRCUIT PROTECTION When the voltage across the sense resistor measured on the Isen pin exceeds 343 mV, short circuit current limit protection gets activated. A comparator inside the ...
Page 14
A. First Cycle 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 inductor current varies during a switching cycle. The current ...
Page 15
FIGURE 9. Inductor Current and Diode Current 15 30150624 www.national.com ...
Page 16
PROGRAMMING THE OUTPUT VOLTAGE The output voltage can be programmed using a resistor di- vider between the output and the FB pin. The resistors are selected such that the voltage at the FB pin is 1.26V. Pick R (the resistor ...
Page 17
This changes the equation for current limit (or R The R and R values may have to be calculated iteratively SEN SL in order to achieve both the desired current limit and stable operation. In some designs R can also ...
Page 18
OUTPUT CAPACITOR SELECTION The output capacitor in a boost converter provides all the out- put current when the inductor is charging result it sees very large ripple currents. The output capacitor should be ca- pable of handling the ...
Page 19
POWER MOSFET SELECTION boost converter, parameters governing the selection of the MOSFET are the minimum threshold voltage the on-resistance the total gate charge, Q (MIN) DS(ON) reverse transfer capacitance and the ...
Page 20
I must be lower than the maximum current rating set by L1PK the current sense resistor. The value of L1 can be increased above the minimum rec- ommended to reduce input ripple and output ripple. However, once D is less ...
Page 21
Other Application Circuit FIGURE 14. Typical Flyback Circuit 21 30150643 www.national.com ...
Page 22
Physical Dimensions www.national.com inches (millimeters) unless otherwise noted 22 ...
Page 23
Notes 23 www.national.com ...
Page 24
... National Semiconductor and the National Semiconductor logo are registered trademarks of National Semiconductor Corporation. All other brand or product names may be trademarks or registered trademarks of their respective holders. ...