LM2267X: Step-Down Voltage Regulator


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To study the functionalities and application of LM2267X buck regulators

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LM2267X: Step-Down Voltage Regulator

  1. 1. LM2267X: Step-Down Voltage Regulator <ul><li>Source: National Semiconductor </li></ul>
  2. 2. Introduction <ul><li>Purpose </li></ul><ul><ul><li>To study the functionalities and application of LM2267X buck regulators. </li></ul></ul><ul><li>Outline </li></ul><ul><ul><li>General Description </li></ul></ul><ul><ul><li>Features </li></ul></ul><ul><ul><li>Block Diagram </li></ul></ul><ul><ul><li>Design Parameters </li></ul></ul><ul><ul><li>Internal Functions </li></ul></ul><ul><li>Content </li></ul><ul><ul><li>14 pages </li></ul></ul><ul><li>Duration </li></ul><ul><ul><li>10 Minutes </li></ul></ul>
  3. 3. Buck Regulator Characteristics <ul><li>Non-Isolated Grounds </li></ul><ul><li>Voltage Step-down Only </li></ul><ul><li>Single Output Only </li></ul><ul><li>Very High Efficiency </li></ul><ul><li>Low Output Ripple Current </li></ul><ul><li>High Input Ripple Current </li></ul><ul><li>High Side (Floating) Gate Drive Required </li></ul><ul><li>Large Achievable Duty Cycle Range </li></ul>
  4. 4. Why use a SIMPLE SWITCHER? <ul><li>The SIMPLE SWITCHER products are supported with an on-line Webench tool suite that helps with the design </li></ul><ul><ul><li>Choosing the components </li></ul></ul><ul><ul><li>Allowing for optimization </li></ul></ul><ul><ul><li>Electrical and thermal simulations </li></ul></ul><ul><ul><li>Building a prototype board </li></ul></ul>
  5. 5. LM2267x Simple Switcher® Series <ul><li>Features: </li></ul><ul><li>Wide Input Voltage Range from 4.5V - 42V </li></ul><ul><li>Load Currents from 0.5A – 5A </li></ul><ul><li>Adjustable and Fixed Output Voltages </li></ul><ul><li>Adjustable and Fixed Switching Frequencies (up to 1MHz) for optimal size and efficiency </li></ul><ul><li>External Soft Start </li></ul><ul><li>Precision Enable </li></ul><ul><li>Internally compensated voltage mode control minimizes external component count </li></ul><ul><li>Vout accurate within 2.0%, worst case </li></ul><ul><li>Adjustable current limit (optional) </li></ul><ul><li>Frequency Sync up to 1MHz </li></ul>
  6. 6. Internal Block Diagram LM22670 Block Diagram
  7. 7. LM2267x Product Information
  8. 8. Precision Enable <ul><li>The precision Enable pin can be used to shut down the power supply. Connecting this pin to GND or to a voltage less than typical 1.6V will completely turn-off the regulator. </li></ul>Note: LM22673/9 does not have enable pin.
  9. 9. Current Limit <ul><li>To be in safe operation area and a design will have an effective current limit function, one of the equations must be hold true. </li></ul>V IN x T BLK x F < V OUT x 0.724 (V IN – V OUT ) xT BLK < (V OUT + V D ) x (1/F) x T BLK
  10. 10. Functions <ul><li>Soft Start </li></ul><ul><ul><li>This feature allows the regulator to gradually reach the initial steady state operating point and reduces start-up stresses and surges. </li></ul></ul><ul><li>Switching Frequency setting and synchronization </li></ul><ul><ul><li>There are 3 different modes for the RT/SYNC pin. </li></ul></ul><ul><li>Boot Pin </li></ul><ul><ul><li>The LM2267x integrates an N-Channel FET switch and associated floating high voltage level shift/gate driver. This gate works along with internal Diode and external bootstrap capicator(0.01uF ceramic cap) </li></ul></ul>
  11. 11. Thermal Protection <ul><li>Internal thermal shutdown circuit protects the LM2267x in the event the maximum junction temperature is exceeded. </li></ul>
  12. 12. Design Parameters <ul><li>Maximum Duty-cycle / Dropout Voltage </li></ul><ul><li>The typical max duty-cycle is 85% at 500Khz switching frequency. The lowest input voltage required to maintain operation is </li></ul><ul><li>Minimum Duty-Cycle: </li></ul><ul><ul><li>There is Minimum on-time which will effect when the output voltage is adjusted very low and the input voltage is very high. </li></ul></ul><ul><li>D = Vout / Vin </li></ul>
  13. 13. Application Information
  14. 14. Current Flow in Buck Application
  15. 15. Additional Resource <ul><li>For ordering the LM2267x, please click the part list or </li></ul><ul><li>Call our sales hotline </li></ul><ul><li>For additional inquires contact our technical service hotline </li></ul><ul><li>For more product information go to </li></ul><ul><ul><li>http://www.national.com/analog/power/simple_switcher_lm2267x_lm22680 </li></ul></ul>Newark Farnell