Datasheet LT8708 (Analog Devices) - 2

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TABLE OF CONTENTS Features ... 1 Applications Information ..26 Applications .. 1
Verify the Power Flow Conditions ...26
Typical Application .. 1
Operating Frequency Selection ...26
Description.. 1
Internal Oscillator ...27
Absolute Maximum Ratings .. 3
SYNC Pin and Clock Synchronization ...27
Order Information .. 3
CLKOUT Pin and Clock Synchronization ...27
Pin Configuration .. 3
Inductor Current Sensing and Slope Compensation .. 27
Electrical Characteristics ... 4
RSENSE Selection and Maximum Current ..28
Typical Performance Characteristics ... 9
RSENSE Selection: Max RSENSE in the
Typical Performance Characteristics ..11
Boost Region ..28
Pin Functions ..13
RSENSE Selection: Max RSENSE in the
Block Diagram ...15
Buck Region ...30
Operation...16
RSENSE Selection: Final RSENSE Value ...31 Typographical Conventions ... 16 RSENSE Filtering ..32 Start-Up .. 16 Inductor (L) Selection ..32 Start-Up: SHDN Pin .. 16 L Selection: Load Current in Buck and Start-Up: SWEN Pin .. 16 Boost Regions ..32 Start-Up: Soft-Start of Switching Regulator ... 17 L Selection: Subharmonic Oscil ations ...33 Control Overview .. 17 L Selection: Maximum Current Rating ..33 Power Switch Control .. 18 Power MOSFET Selection ...34 Switch Control: Buck Region (VIN >> VOUT) ... 19 CIN and COUT Selection ...37 Switch Control: Buck-Boost (VIN ≅ VOUT) ... 19 Schottky Diode (D1, D2, D3, D4) Selection ...38 Switch Control: Boost Region (VIN << VOUT) ..20 Topside MOSFET Driver Supply (CB1, DB1, CB2, DB2) ... 39 Switch Control: Soft-Start ..20 Top Driver: Boost Cap Charge Control Block ..39 Uni and Bidirectional Conduction ..20 Top Driver: Boost Diodes DB1 and DB2 ...39 Bidirectional Conduction: CCM ..21 VINHIMON, VOUTLOMON and RVSOFF ..39 Unidirectional Conduction: DCM ...21 IIN and IOUT Current Monitoring and Limiting ...42 Unidirectional Conduction: HCM ...22 Loop Compensation ..44 Unidirectional Conduction: Burst Mode ..22 INTVCC Regulators and EXTVCC Connection ...45 Error Amplifiers ..22 LDO33 Regulator ..45 VOUT Regulation and Sensing ...23 Voltage Lockouts ..46 VOUT: Regulation ...23 Junction Temperature Measurement ..46 VOUT: Above Regulation ..23 Thermal Shutdown ...47 VOUT: Below Regulation and Undervoltage ...23 Efficiency Considerations ..47 VIN Regulation and Sensing ..24 Circuit Board Layout Checklist ...47 VIN: Regulation ...24 Hot Plugging Considerations ...49 VIN: Above Regulation and Overvoltage ..24 Design Example ..49 VIN: Below Regulation ...24
Typical Applications ..55
Current Monitoring and Limiting ... 24
Package Description ...63
Monitoring and Limiting: IMON Pins .. 24
Typical Application ...64
Monitoring: ICP and ICN Pins ...25
Related Parts ..64
INTVCC/EXTVCC/GATEVCC/LDO33 Power ...25 CLKOUT and Temperature Sensing ...25 Rev 0 2 For more information www.analog.com Document Outline Features Applications Typical Application Description Absolute Maximum Ratings Order Information Pin Configuration Electrical Characteristics Typical Performance Characteristics Typical Performance Characteristics Pin Functions Block Diagram Operation Typographical Conventions Start-Up Start-Up: SHDN Pin Start-Up: SWEN Pin Start-Up: Soft-Start of Switching Regulator Control Overview Power Switch Control Switch Control: Buck Region (VIN >> VOUT) Switch Control: Buck-Boost (VIN ≅ VOUT) Switch Control: Boost Region (VIN << VOUT) Switch Control: Soft-Start Uni and Bidirectional Conduction Bidirectional Conduction: CCM Unidirectional Conduction: DCM Unidirectional Conduction: HCM Unidirectional Conduction: Burst Mode Error Amplifiers VOUT Regulation and Sensing VOUT: Regulation VOUT: Above Regulation VOUT: Below Regulation and Undervoltage VIN Regulation and Sensing VIN: Regulation VIN: Above Regulation and Overvoltage VIN: Below Regulation Current Monitoring and Limiting Monitoring and Limiting: IMON Pins Monitoring: ICP and ICN Pins INTVCC/EXTVCC/GATEVCC/LDO33 Power CLKOUT and Temperature Sensing Applications Information Verify the Power Flow Conditions Operating Frequency Selection Internal Oscillator SYNC Pin and Clock Synchronization CLKOUT Pin and Clock Synchronization Inductor Current Sensing and Slope Compensation RSENSE Selection and Maximum Current RSENSE Selection: Max RSENSE in the Boost Region RSENSE Selection: Max RSENSE in the Buck Region RSENSE Selection: Final RSENSE Value RSENSE Filtering Inductor (L) Selection L Selection: Load Current in Buck and Boost Regions L Selection: Subharmonic Oscillations L Selection: Maximum Current Rating Power MOSFET Selection CIN and COUT Selection Schottky Diode (D1, D2, D3, D4) Selection Topside MOSFET Driver Supply (CB1, DB1, CB2, DB2) Top Driver: Boost Cap Charge Control Block Top Driver: Boost Diodes DB1 and DB2 VINHIMON, VOUTLOMON and RVSOFF IIN and IOUT Current Monitoring and Limiting Loop Compensation INTVCC Regulators and EXTVCC Connection LDO33 Regulator Voltage Lockouts Junction Temperature Measurement Thermal Shutdown Efficiency Considerations Circuit Board Layout Checklist Hot Plugging Considerations Design Example Typical Applications Package Description Typical Application Related Parts