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LM3420 데이터시트(PDF) 11 Page - Texas Instruments |
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LM3420 데이터시트(HTML) 11 Page - Texas Instruments |
11 / 26 page LM3420 www.ti.com SNVS116E – MAY 1998 – REVISED DECEMBER 2014 Feature Description (continued) • Rf ≈ 181 kΩ (1) The resistor (Rf) in the formula is an internal resistor located on the die. Since this resistor value affects the phase margin, the worst case maximum and minimum values are important when analyzing closed loop stability. The minimum and maximum room temperature values of this resistor are specified in the LM3420 Electrical Characteristics section of this data sheet, and a curve showing the temperature coefficient is shown in the curves section. Minimum values of Rf result in lower phase margins. 8.3.2 VREG External Voltage Trim The regulation voltage (VREG) of the LM3420 can be externally trimmed by adding a single resistor from the COMP pin to the +IN pin or from the COMP pin to the GND pin, depending on the desired trim direction. Trim adjustments up to ±10% of VREG can be realized, with only a small increase in the temperature coefficient. (See temperature coefficient curve shown in Figure 11.) Figure 11. Normalized Temperature Drift With Output Externally Trimmed Decreasing VREG Figure 12. Increasing VREG Figure 13. Changing VREG Formula for selecting trim resistor values is shown in Equation 2 and Equation 3, based on the percent of increase (%incr) or percent of decrease (%decr) of the output voltage from the nominal voltage. Rincrease = 26 × 10 5/%incr (2) Rdecrease = (154 × 10 5/%decr) − 181 × 103 (3) 8.4 Device Functional Modes 8.4.1 Operation as Control Section The LM3420 is monolithic integrated circuits, which is suitable for charging and end-of-charge control for Lithium- Ion rechargeable batteries. In this application, LM3420 is the reference and control section in the overall feedback loop. The regulated voltage is sensed between the IN pin and GND pin. If the voltage at the IN pin is less than the regulating voltage (VREG), the OUT pin sources no current. As the voltage at the IN pin approaches the VREG, the OUT pin begins sourcing current, which can drive a feedback device or a power device. Copyright © 1998–2014, Texas Instruments Incorporated Submit Documentation Feedback 11 Product Folder Links: LM3420 |
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