Datasheet LT8708 (Analog Devices) - 7

LT8708
ELECTRICAL CHARACTERISTICS The
l
denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VINCHIP = 12V, SHDN = 3V, DIR = 3.3V unless otherwise noted (Note 3). PARAMETER CONDITIONS MIN TYP MAX UNITS
IMON_OP, IMON_ON, ICP and ICN Max l 120 μA Output Current IMON_OP Error Amp EA6 gm 190 μmho IMON_OP Error Amp EA6 Voltage Gain 130 V/V IMON_ON Error Amp EA2 gm FBIN = 0V, FBOUT = 3.3V 190 μmho IMON_ON Error Amp EA2 Voltage Gain FBIN = 0V, FBOUT = 3.3V 130 V/V
NMOS Gate Drivers
TG1, TG2 Rise Time CLOAD = 3300pF (Note 4) 20 ns TG1, TG2 Fall Time CLOAD = 3300pF (Note 4) 20 ns BG1, BG2 Rise Time CLOAD = 3300pF (Note 4) 20 ns BG1, BG2 Fall Time CLOAD = 3300pF (Note 4) 20 ns TG1 Off to BG1 On Delay CLOAD = 3300pF Each Driver 90 ns BG1 Off to TG1 On Delay CLOAD = 3300pF Each Driver 80 ns TG2 Off to BG2 On Delay CLOAD = 3300pF Each Driver 90 ns BG2 Off to TG2 On Delay CLOAD = 3300pF Each Driver 80 ns Minimum On-Time for Main Switch in Boost Switch M3, CLOAD = 3300pF 200 ns Operation (tON(M3,MIN)) Minimum On-Time for Synchronous Switch in Buck Switch M2, CLOAD = 3300pF 200 ns Operation (tON(M2,MIN)) Minimum Off-Time for Main Switch in Steady-State Switch M3, CLOAD = 3300pF 230 ns Boost Operation Minimum Off-Time for Synchronous Switch in Switch M2, CLOAD = 3300pF 230 ns Steady-State Buck Operation
Oscillator
Switch Frequency Range SYNCing or Free Running 100 400 kHz Switching Frequency, FOSC RT = 365k l 102 120 142 kHz RT = 215k l 170 202 235 kHz RT = 124k l 310 350 400 kHz SYNC High Level for Synchronization l 1.3 V SYNC Low Level for Synchronization l 0.5 V SYNC Clock Pulse Duty Cycle VSYNC = 0V to 2V 20 80 % Recommended Min SYNC Ratio FSYNC/FOSC 3/4 CLKOUT Output Voltage High VLDO33 – VCLKOUT, 1mA Out of CLKOUT Pin, 100 250 mV ILDO33 = 0μA CLKOUT Output Voltage Low 1mA Into CLKOUT Pin 25 100 mV CLKOUT Duty Cycle TJ = –40°C 22.7 % TJ = 25°C 44.1 % TJ = 125°C 77 % Rev 0 For more information www.analog.com 7 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