Datasheet LTC7897 (Analog Devices) - 2

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Data Sheet LTC7897 TABLE OF CONTENTS
Features .. 1 Applications ... 1 General Description ... 1 Typical Application .. 1 Revision History ... 3 Specifications ... 4 Absolute Maximum Ratings .. 9 Pin Configurations and Function Descriptions .. 11 Block Diagram .. 14 Typical Performance Characteristics ... 15 Theory of Operation .. 20 Main Control Loop ... 20 Power and Bias Supplies (VIN, EXTVCC, DRVCC, and INTVCC) .. 20 High-Side Bootstrap Capacitor .. 20 Dead Time Control (DTCA and DTCB Pins) .. 20 Start-Up and Shutdown (RUN, OVLO, and TRACK/SS Pins) ... 21 Light Load Operation: Burst Mode Operation, Pulse-Skipping Mode, or Forced Continuous Mode (MODE Pin) ... 21 Frequency Selection, Spread Spectrum, and PhaseLocked Loop (FREQ and PLLIN/SPREAD Pins) ... 22 Input Supply Overvoltage Lockout (OVLO Pin) ... 23 Output Overvoltage Protection .. 23 Foldback Current .. 23 Power Good ... 23 Applications Information .. 24 Inductor Value Calculation ... 24 Inductor Core Selection .. 24 Current Sense Selection ... 24 Low Value Resistor Current Sensing .. 25 Inductor DCR Current Sensing ... 26 Setting the Operating Frequency .. 27 Selecting the Light-Load Operating Mode .. 28 Dead Time Control (DTCA and DTCB Pins) .. 29 DTCX Pins Tied to INTVCC or Ground (Adaptive Dead Time Control) .. 29 DTCX Pin Connected with a Resistor to GND ... 30 Power MOSFET Selection ... 31
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Rev. A 2 of 53 Document Outline Features Applications General Description Typical Application TABLE OF CONTENTS Revision History Specifications Absolute Maximum Ratings Pin Configurations and Function Descriptions Block Diagram Typical Performance Characteristics Theory of Operation Main Control Loop Power and Bias Supplies (VIN, EXTVCC, DRVCC, and INTVCC) High-Side Bootstrap Capacitor Dead Time Control (DTCA and DTCB Pins) Start-Up and Shutdown (RUN, OVLO, and TRACK/SS Pins) Light Load Operation: Burst Mode Operation, Pulse-Skipping Mode, or Forced Continuous Mode (MODE Pin) Frequency Selection, Spread Spectrum, and PhaseLocked Loop (FREQ and PLLIN/SPREAD Pins) Input Supply Overvoltage Lockout (OVLO Pin) Output Overvoltage Protection Foldback Current Power Good Applications Information Inductor Value Calculation Inductor Core Selection Current Sense Selection Low Value Resistor Current Sensing Inductor DCR Current Sensing Setting the Operating Frequency Selecting the Light-Load Operating Mode Dead Time Control (DTCA and DTCB Pins) DTCX Pins Tied to INTVCC or Ground (Adaptive Dead Time Control) DTCX Pin Connected with a Resistor to GND Power MOSFET Selection CIN and COUT Selection Setting the Output Voltage RUN Pin and Overvoltage/Undervoltage Lockout Soft-Start and Tracking (TRACK/SS Pin) DRVCC and INTVCC Regulators (OPTI-DRIVE) Topside MOSFET Driver Supply (CB, DB) Minimum On-Time Considerations Fault Conditions: Current Limit and Foldback Fault Conditions: Overvoltage Protection Fault Conditions: Overtemperature Protection Phase-Locked Loop and Frequency Synchronization Efficiency Considerations Checking Transient Response Design Example PC Board Layout Checklist PC Board Layout Debugging Typical Application Related Parts Outline Dimensions Ordering Guide