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LM2940QML 数据表(PDF) 11 Page - Texas Instruments |
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LM2940QML 数据表(HTML) 11 Page - Texas Instruments |
11 / 17 page LM2940QML, LM2940QML-SP www.ti.com SNVS389B – MAY 2010 – REVISED MAY 2013 Typical Application *Required if regulator is located far from power supply filter. **COUT must be at least 22 μF to maintain stability. May be increased without bound to maintain regulation during transients. Locate as close as possible to the regulator. This capacitor must be rated over the same operating temperature range as the regulator and the ESR is critical; see curve. APPLICATION HINTS EXTERNAL CAPACITORS The output capacitor is critical to maintaining regulator stability, and must meet the required conditions for both ESR (Equivalent Series Resistance) and minimum amount of capacitance. MINIMUM CAPACITANCE: The minimum output capacitance required to maintain stability is 22 μF (this value may be increased without limit). Larger values of output capacitance will give improved transient response. ESR LIMITS: The ESR of the output capacitor will cause loop instability if it is too high or too low. The acceptable range of ESR plotted versus load current is shown in the graph below. It is essential that the output capacitor meet these requirements, or oscillations can result. Figure 20. Output Capacitor ESR Limits It is important to note that for most capacitors, ESR is specified only at room temperature. However, the designer must ensure that the ESR will stay inside the limits shown over the entire operating temperature range for the design. For aluminum electrolytic capacitors, ESR will increase by about 30X as the temperature is reduced from 25°C to −40°C. This type of capacitor is not well-suited for low temperature operation. Solid tantalum capacitors have a more stable ESR over temperature, but are more expensive than aluminum electrolytics. A cost-effective approach sometimes used is to parallel an aluminum electrolytic with a solid Tantalum, with the total capacitance split about 75/25% with the Aluminum being the larger value. If two capacitors are paralleled, the effective ESR is the parallel of the two individual values. The “flatter” ESR of the Tantalum will keep the effective ESR from rising as quickly at low temperatures. Copyright © 2010–2013, Texas Instruments Incorporated Submit Documentation Feedback 11 Product Folder Links: LM2940QML LM2940QML-SP |
类似零件编号 - LM2940QML |
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类似说明 - LM2940QML |
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