LM3743 High Performance Controller with Comprehensive Fault Protection
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LM3743 High Performance Controller with Comprehensive Fault Protection Features Designed High Reliability Systems AN-1669
LM3743 High Performance Controller with Comprehensive Fault Protection Features Designed High Reliability Systems
LM3743 DC-DC voltage mode buck controller featuring synchronous rectification MHz. deliver current high step down from input voltage between 5.5V down minimum output voltage 0.8V. highly integrated device small MSOP-10 package. Features include; pre-biased soft-start, tracking capability, comprehensive fault protection features suitable high reliability systems such rack mounted servers telecom base station subsystems.
National Semiconductor Application Note 1669 Ricardo Capetillo June 2007
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FIGURE Hiccup Time Internal Soft-Start help quantify power consumption during persistent fault condition, examine application with lowside current limit. Once overload, low-side current limit controls valley current only allows average plus ripple current pass through inductor MOSFETs. Hiccup mode initializes after switching cycles allowing only very small temperature rise. Once hiccup mode, average current through high-side
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IHSF-AVE (ICLIM [D(15 cycles TSW) With arbitrary 60%, ripple current switching frequency. average current through low-side ILSF-AVE (ICLIM [(1-D) cycles TSW) average current through inductor IL-AVE (ICLIM cycles TSW) Protecting Typical Fault Conditions High-Reliability Systems Server racks telecom base station subsystems require high reliability enable uninterrupted flow data communication. When unexpected failures occur, LM3743 fault protection features help prevent further electrical thermal stress. Examining some typical system fault conditions, elaborate protection modes LM3743 device operational benefit: capacitor such POS-cap located output LM3743 fails short circuit after over-voltage surge exceeds maximum capacitor voltage rating, refer Figure such situation duty cycle inductor current increase cycle cycle, fortunately input current decreased because LM3743s' initializes Hiccup-Mode. small piece metal falling into product from outside piece metal that loose product changes positions during shipment lands across
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FIGURE Typical Application Circuit Data center facilities telecom base station subsystems must manage balance essential commodities power cooling capacity. example, processors rack mounted servers demand large amounts power greatest sources heat during normal operation. Substantial increases heat during normal operation fault conditions will reduce reliability many components server racks including semiconductor components, hard drives, fans. LM3743 will minimize power consumption during fault conditions thereby reducing thermal loads increasing reliability. LM3743 Comprehensive Fault Protection Features LM3743 provides following comprehensive fault protection features: high side current limit (HSCL), output undervoltage protection (UVP), side current limit (LSCL). When engaged, these three features each independently initiate hiccup protection mode which disables both highside low-side FETs begin cool down period Figure conclusion this cool down period, LM3743 performs internal soft-start check removal fault condition continue normal operation. Hiccup protection mode enables system designer avoid need over design components thermal runaway during fault conditions resulting lower bill material cost.
2007 National Semiconductor Corporation
300270
AN-1669
switch node (VSW) ground, Figure High side current limit immediately senses short circuit fault condition. Excessive load and/or incorrect selection MOSFET results open circuit failure. example; side MOSFET (Q2) fails, depicted Figure inductor current will flow during time should thus inductor current will increase cycle cycle. high side current limit will capture over current event, thereby protecting high side MOSFET (Q1) from over heating failure.
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FIGURE Side MOSFET Open-Circuit Failure these situations LM3743 provides fault protection, reduces average input current relieves power components from thermal stress during persistent fault conditions. After removal fault condition, LM3743 performs automatic self test recovery sequence. User intervention required, reduces maintenance cost designed circuit complexity. LM3743 provides comprehensive fault protection reduction server power consumption during fault conditions. also combines high efficiency with high drive capabilities loads 20A. With LM3743, balance between power cooling capacity much more manageable during device failure short circuit conditions. datasheet, evaluation board, application note, reference design information www.national.com/pf/LM/ LM3743.html.
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FIGURE Output Short-Circuit Ground
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FIGURE Switch Node Short-Circuit Ground
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Notes
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LM3743 High Performance Controller with Comprehensive Fault Protection Features Designed High Reliability Systems
Notes
CONTENTS THIS DOCUMENT PROVIDED CONNECTION WITH NATIONAL SEMICONDUCTOR CORPORATION ("NATIONAL") PRODUCTS. NATIONAL MAKES REPRESENTATIONS WARRANTIES WITH RESPECT ACCURACY COMPLETENESS CONTENTS THIS PUBLICATION RESERVES RIGHT MAKE CHANGES SPECIFICATIONS PRODUCT DESCRIPTIONS TIME WITHOUT NOTICE. LICENSE, WHETHER EXPRESS, IMPLIED, ARISING ESTOPPEL OTHERWISE, INTELLECTUAL PROPERTY RIGHTS GRANTED THIS DOCUMENT. TESTING OTHER QUALITY CONTROLS USED EXTENT NATIONAL DEEMS NECESSARY SUPPORT NATIONAL'S PRODUCT WARRANTY. EXCEPT WHERE MANDATED GOVERNMENT REQUIREMENTS, TESTING PARAMETERS EACH PRODUCT NECESSARILY PERFORMED. NATIONAL ASSUMES LIABILITY APPLICATIONS ASSISTANCE BUYER PRODUCT DESIGN. BUYERS RESPONSIBLE THEIR PRODUCTS APPLICATIONS USING NATIONAL COMPONENTS. PRIOR USING DISTRIBUTING PRODUCTS THAT INCLUDE NATIONAL COMPONENTS, BUYERS SHOULD PROVIDE ADEQUATE DESIGN, TESTING OPERATING SAFEGUARDS. EXCEPT PROVIDED NATIONAL'S TERMS CONDITIONS SALE SUCH PRODUCTS, NATIONAL ASSUMES LIABILITY WHATSOEVER, NATIONAL DISCLAIMS EXPRESS IMPLIED WARRANTY RELATING SALE AND/OR NATIONAL PRODUCTS INCLUDING LIABILITY WARRANTIES RELATING FITNESS PARTICULAR PURPOSE, MERCHANTABILITY, INFRINGEMENT PATENT, COPYRIGHT OTHER INTELLECTUAL PROPERTY RIGHT. LIFE SUPPORT POLICY NATIONAL'S PRODUCTS AUTHORIZED CRITICAL COMPONENTS LIFE SUPPORT DEVICES SYSTEMS WITHOUT EXPRESS PRIOR WRITTEN APPROVAL CHIEF EXECUTIVE OFFICER GENERAL COUNSEL NATIONAL SEMICONDUCTOR CORPORATION. used herein: Life support devices systems devices which intended surgical implant into body, support sustain life whose failure perform when properly used accordance with instructions provided labeling reasonably expected result significant injury user. critical component component life support device system whose failure perform reasonably expected cause failure life support device system affect safety effectiveness. National Semiconductor National Semiconductor logo registered trademarks National Semiconductor Corporation. other brand product names trademarks registered trademarks their respective holders.
Copyright© 2007 National Semiconductor Corporation
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