Datasheet LT8708 (Analog Devices) - 9

link to page 59 link to page 59 link to page 59 LT8708
TYPICAL PERFORMANCE CHARACTERISTICS Efficiency vs Output Current Efficiency vs Output Current Efficiency vs Output Current (Boost Region – Page 59 ) (Buck Region – Page 59) (Buck–Boost Region – Page 59)
100 100 100 90 90 90 80 80 80 70 70 70 60 60 60 50 50 50 40 40 40 EFFICIENCY (%) EFFICIENCY (%) EFFICIENCY (%) 30 VIN = 38V 30 VIN = 51.5V 30 VIN = 48V VOUT = 47.4V VOUT = 47.4V VOUT = 47.4V 20 HCM 20 HCM 20 HCM 10 DCM 10 DCM 10 DCM CCM CCM CCM 0 0 0 0.01 0.1 1 10 0.01 0.1 1 10 0.01 0.1 1 10 LOAD CURRENT (A) LOAD CURRENT (A) LOAD CURRENT (A) 8708 G01 8708 G02 8708 G03
Feedback Voltages Feedback V Feedback Voltages (Five Parts) Oscillator Frequency
1.23 1.23 400 VC = 1.2V VC = 1.2V RT = 124k 350 1.22 1.22 300 1.21 1.21 250 RT = 215k TAGE (V) 1.20 TAGE (V) 1.20 200 FBOUT 150 PIN VOL 1.19 PIN VOL 1.19 RT = 365k FBIN FREQUENCY (kHz) IMON_INP 100 1.18 IMON_INN 1.18 IMON_ON 50 IMON_OP 1.17 1.17 0 –45 –20 5 30 55 80 105 130 155 –45 –20 5 30 55 80 105 130 155 –45 –20 5 30 55 80 105 130 155 TEMPERATURE (°C) TEMPERATURE (°C) TEMPERATURE (°C) 8708 G04 8708 G05 8708 G06
Maximum Inductor Current Sense Inductor Current Sense Voltage at Maximum Inductor Current Sense Voltage vs Duty Cycle Minimum Duty Cycle Voltage at Minimum Duty Cycle V
140 100 100 120 80 80 120 BOOST REGION BUCK REGION 60 60 100 100 40 40 CSP–CSN (mV) 80 80 20 20 BUCK REGION BUCK REGION 0 0 60 60 BOOST REGION BOOST REGION –20 –20 |CSP–CSN| (mV) CSN–CSP (mV) |CSP–CSN| (mV) 40 40 –40 –40 –60 –60 20 20 –80 –80 0 –100 –100 0 0 20 40 60 80 100 0.5 1 1.5 2 –45 –20 5 30 55 80 105 130 155 M2 OR M3 DUTY CYCLE (%) VC (V) TEMPERATURE (°C) 8708 G07 8708 G08 8708 G09 Rev 0 For more information www.analog.com 9 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