Datasheet LT8708 (Analog Devices)
| Manufacturer | Analog Devices |
| Description | 80V Synchronous 4-Switch Buck-Boost DC/DC Controller with Bidirectional Capability |
| Pages / Page | 64 / 1 — FEATURES. DESCRIPTION. Single Inductor Allows VIN Above, Below, or. … |
| Revision | A |
| File Format / Size | PDF / 3.9 Mb |
| Document Language | English |
FEATURES. DESCRIPTION. Single Inductor Allows VIN Above, Below, or. Equal to VOUT. Six Independent Forms of Regulation
Model Line for this Datasheet
Text Version of Document
LT8708 80V Synchronous 4-Switch Buck-Boost DC/DC Controller with Flexible Bidirectional Capability
FEATURES DESCRIPTION
n
Single Inductor Allows VIN Above, Below, or
The LT®8708 is a high performance buck-boost switching
Equal to VOUT
regulator controller that operates from an input voltage n
Six Independent Forms of Regulation
that can be above, below or equal to the output voltage. n
VIN Current (Forward and Reverse)
Features are included to simplify bidirectional power n
VOUT Current (Forward and Reverse)
conversion in battery/capacitor backup systems and other n
VIN and VOUT Voltage
applications that may need regulation of VOUT, VIN, IOUT, n
Forward and Reverse Discontinuous Conduction
and/or IIN. Forward and reverse current can be monitored
Mode Supported
and limited for the input and output sides of the converter. n
Supports MODE and DIR Pin Changes While Switching
All four current limits (forward input, reverse input, forward n
VINCHIP Range 2.8V (Need EXTVCC > 6.4V) to 80V
output and reverse output) can be set independently using n
VOUT Range: 1.3V to 80V
four resistors on the PCB. n
Synchronous Rectification: Up to 99% Efficiency
The MODE pin can select between discontinuous conduc- n Available in 40-Lead (5mm × 8mm) QFN with High tion mode (DCM), continuous conduction mode (CCM), Voltage Pin Spacing hybrid conduction mode (HCM) and Burst Mode® operation. In combination with the DIR (direction) pin, the chip can be
APPLICATIONS
configured to process power only from VIN to VOUT or only n from V High Voltage Buck-Boost Converters OUT to VIN. With a wide 2.8V to 80V input and 1.3V n to 80V output range, the LT8708 is compatible with most Bidirectional Charging System n solar, automotive, telecom and battery-powered systems. Automotive 48V Systems All registered trademarks and trademarks are the property of their respective owners.
TYPICAL APPLICATION 12V Bidirectional Dual Battery System with FHCM and RHCM
ILIM ILIM V V BAT1 BAT2 + + 10V + + 10V
Efficiency
TO 16V TO 16V
EFFICIENCY
BATTERY – TO DIODE TO DIODE – BATTERY DB1 DB2 100 99 TG1 BOOST1 SW1 BG1 CSP CSN GND BG2 SW2 BOOST2 TG2 98 CSNIN CSPOUT POWER TRANSFER CSNOUT DECISION LOGIC CSPIN EXTVCC VINCHIP 97 VOUTLOMON SHDN FBOUT FBIN INTVCC LT8708 VINHIMON EFFICIENCY (%) 96 GATEVCC RVS (0V) FWD (3V) DIR IMON_OP IMON_ON LD033 SWEN ICN 95 ICP LDO33 VBAT2 = 13.5V IMON_INP D RVSOFF IMON_INN B1 DB2 IOUT = 15A MODE VC RT SS SYNC CLKOUT TO TO 94 8708 TA01a BOOST1 BOOST2 10 12 14 16 126kHz VBAT1 (V) 8708 TA01b Rev 0 Document Feedback For more information www.analog.com 1 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
FEATURES DESCRIPTION
n
Single Inductor Allows VIN Above, Below, or
The LT®8708 is a high performance buck-boost switching
Equal to VOUT
regulator controller that operates from an input voltage n
Six Independent Forms of Regulation
that can be above, below or equal to the output voltage. n
VIN Current (Forward and Reverse)
Features are included to simplify bidirectional power n
VOUT Current (Forward and Reverse)
conversion in battery/capacitor backup systems and other n
VIN and VOUT Voltage
applications that may need regulation of VOUT, VIN, IOUT, n
Forward and Reverse Discontinuous Conduction
and/or IIN. Forward and reverse current can be monitored
Mode Supported
and limited for the input and output sides of the converter. n
Supports MODE and DIR Pin Changes While Switching
All four current limits (forward input, reverse input, forward n
VINCHIP Range 2.8V (Need EXTVCC > 6.4V) to 80V
output and reverse output) can be set independently using n
VOUT Range: 1.3V to 80V
four resistors on the PCB. n
Synchronous Rectification: Up to 99% Efficiency
The MODE pin can select between discontinuous conduc- n Available in 40-Lead (5mm × 8mm) QFN with High tion mode (DCM), continuous conduction mode (CCM), Voltage Pin Spacing hybrid conduction mode (HCM) and Burst Mode® operation. In combination with the DIR (direction) pin, the chip can be
APPLICATIONS
configured to process power only from VIN to VOUT or only n from V High Voltage Buck-Boost Converters OUT to VIN. With a wide 2.8V to 80V input and 1.3V n to 80V output range, the LT8708 is compatible with most Bidirectional Charging System n solar, automotive, telecom and battery-powered systems. Automotive 48V Systems All registered trademarks and trademarks are the property of their respective owners.
TYPICAL APPLICATION 12V Bidirectional Dual Battery System with FHCM and RHCM
ILIM ILIM V V BAT1 BAT2 + + 10V + + 10V
Efficiency
TO 16V TO 16V
EFFICIENCY
BATTERY – TO DIODE TO DIODE – BATTERY DB1 DB2 100 99 TG1 BOOST1 SW1 BG1 CSP CSN GND BG2 SW2 BOOST2 TG2 98 CSNIN CSPOUT POWER TRANSFER CSNOUT DECISION LOGIC CSPIN EXTVCC VINCHIP 97 VOUTLOMON SHDN FBOUT FBIN INTVCC LT8708 VINHIMON EFFICIENCY (%) 96 GATEVCC RVS (0V) FWD (3V) DIR IMON_OP IMON_ON LD033 SWEN ICN 95 ICP LDO33 VBAT2 = 13.5V IMON_INP D RVSOFF IMON_INN B1 DB2 IOUT = 15A MODE VC RT SS SYNC CLKOUT TO TO 94 8708 TA01a BOOST1 BOOST2 10 12 14 16 126kHz VBAT1 (V) 8708 TA01b Rev 0 Document Feedback For more information www.analog.com 1 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
