データシートサーチシステム |
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LM3100MH データシート(PDF) 10 Page - Texas Instruments |
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LM3100MH データシート(HTML) 10 Page - Texas Instruments |
10 / 21 page ICL IPK 'I IOCL IOUT Load Current Increases Normal Operation Current Limited 'I = (VIN - VOUT) x tON L LM3100 STOP RUN VIN VIN EN LM3100 SNVS421F – JANUARY 2006 – REVISED DECEMBER 2009 www.ti.com Figure 2. Shutdown Implementation Current Limit Current limit detection occurs during the off-time by monitoring the re-circulating current through the low-side synchronous switch. Referring to Functional Block Diagram, when the buck switch is turned off, inductor current flows through the load, into PGND, and through the internal low-side synchronous switch. If that current exceeds 1.9A the current limit comparator toggles, forcing a delay to the start of the next on-time period. The next cycle starts when the re-circulating current falls back below 1.9A and the voltage at FB is below 0.8V. The inductor current is monitored during the low-side switch on-time. As long as the overload condition persists and the inductor current exceeds 1.9A, the high-side switch will remain inhibited. The operating frequency is lower during an over-current due to longer than normal off-times. Figure 3 illustrates an inductor current waveform, the average inductor current is equal to the output current, IOUT in steady state. When an overload occurs, the inductor current will increase until it exceeds the current limit threshold, 1.9A. Then the control keeps the high-side switch off until the inductor current ramps down below 1.9A. Within each on-time period, the current ramps up an amount equal to: (6) During this time the LM3100 is in a constant current mode, with an average load current (IOCL) equal to 1.9A + ΔI/2. Figure 3. Inductor Current - Current Limit Operation N-Channel Buck Switch and Driver The LM3100 integrates an N-Channel buck (high-side) switch and associated floating high voltage gate driver. The gate drive circuit works in conjunction with an external bootstrap capacitor and an internal high voltage diode. A 33 nF capacitor (CBST) connected between BST and SW pins provides voltage to the high-side driver during the buck switch on-time. During each off-time, the SW pin falls to approximately -1V and CBST charges from the VCC supply through the internal diode. The minimum off-time of 260ns ensures adequate time each cycle to recharge the bootstrap capacitor. 10 Submit Documentation Feedback Copyright © 2006–2009, Texas Instruments Incorporated Product Folder Links: LM3100 |
同様の部品番号 - LM3100MH |
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同様の説明 - LM3100MH |
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