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LM2841 データシート(PDF) 7 Page - Texas Instruments |
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LM2841 データシート(HTML) 7 Page - Texas Instruments |
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7 / 20 page  Max Duty Cycle Limit OSC DC LIMIT SET + + - + PWM Comp RESET FET Driver BUCK DRIVE + - Error Amp FB Bandgap Soft Start Thermal Shutdown TSD SHDN Inductor Current Measurement CB SW GND UVLO Comp BG UVLO Voltage Regulator VIN LM2841, LM2842 www.ti.com SNVS540H – MARCH 2009 – REVISED APRIL 2013 BLOCK DIAGRAM Figure 13. Block Diagram OPERATION PROTECTION The LM2840/1/2 has dedicated protection circuitry running during normal operation to protect the IC. The thermal shutdown circuitry turns off the power device when the die temperature reaches excessive levels. The UVLO comparator protects the power device during supply power startup and shutdown to prevent operation at voltages less than the minimum input voltage. A gate drive (CB) under-voltage lockout is included to ensure that there is enough gate drive voltage to drive the MOSFET before the device tries to start switching. The LM2840/1/2 also features a shutdown mode decreasing the supply current to approximately 16 µA. CONTINUOUS CONDUCTION MODE The LM2840/1/2 contains a current-mode, PWM buck regulator. A buck regulator steps the input voltage down to a lower output voltage. In continuous conduction mode (when the inductor current never reaches zero at steady state), the buck regulator operates in two cycles. The power switch is connected between VIN and SW. In the first cycle of operation the transistor is closed and the diode is reverse biased. Energy is collected in the inductor and the load current is supplied by COUT and the rising current through the inductor. During the second cycle the transistor is open and the diode is forward biased due to the fact that the inductor current cannot instantaneously change direction. The energy stored in the inductor is transferred to the load and output capacitor. The ratio of these two cycles determines the output voltage. The output voltage is defined approximately as: D=VOUT/VIN and D’ = (1-D) where D is the duty cycle of the switch. D and D' will be required for design calculations. DESIGN PROCEDURE This section presents guidelines for selecting external components. SETTING THE OUTPUT VOLTAGE The output voltage is set using the feedback pin and a resistor divider connected to the output as shown on the front page schematic. The feedback pin voltage 0.765V, so the ratio of the feedback resistors sets the output voltage according to the following equation: VOUT=0.765V(1+(R1/R2)) Typically R2 will be given as 100 Ω-10 kΩ for a starting value. To solve for R1 given R2 and VOUT use R1=R2((VOUT/0.765V)-1). Copyright © 2009–2013, Texas Instruments Incorporated Submit Documentation Feedback 7 Product Folder Links: LM2841 LM2842 |
同様の部品番号 - LM2841 |
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同様の説明 - LM2841 |
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