DC2596A Analog Devices

LT8708-1 80V Synchronous 4-Switch Buck-Boost DC/DC Slave Controller for LT8708 Multiphase System FEATURES DESCRIPTION n Slave Chip of LT8708 to Deliver Additional Power The LT 8708-1 is a high performance buck-boost n Good Current Matching to the Average Output switching regulator controller that is paralleled with the Current of LT8708 Through Current Regulation LT8708 to add power and phases to an LT8708 system. n Easily Paralleled with LT8708 Through Four Pins The LT8708-1 always operates as a slave to the master n Synchronized Start-Up with LT8708 LT8708 and has the capability of delivering as much cur- n Same Conduction Modes as LT8708 rent or power as the master. One or more slaves can be n Synchronous Rectification: Up to 98% Efficiency connected to a single master, proportionally increasing n Frequency Range: 100kHz to 400kHz power and current capability of the system. n Available in 40-Lead (5mm 8mm) QFN with High The LT8708-1 has the same conduction modes as LT8708, Voltage Pin Spacing and 64-Lead (10mm 10mm) allowing the LT8708-1 to conduct current and power in eLQFP the same direction(s) as the master. The master controls n AEC-Q100 in Progress the overall current and voltage limits for an LT8708 mul- tiphase system, and the slaves comply with these limits. APPLICATIONS LT8708-1s can be easily paralleled with the LT8708 by n High Voltage Buck-Boost Converters connecting four signals together. Two additional current n Bidirectional Charging Systems limits (forward V current and reverse V current) are IN IN n Automotive 48V Systems available on each slave that can be set independently. 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TYPICAL APPLICATION The LT8708-1 Two-Phase 12V Bidirectional Dual Battery System with FHCM and RHCM Efficiency 100 V V BAT2 BAT1 10V TO 16V 10V TO BATTERY 16V 99 BATTERY 98 TO DIODE TO DIODE DB1 DB2 97 96 TG1 BOOST1 SW1 BG1 CSP CSN GND BG2 SW2 BOOST2 TG2 95 V = 13.5V BAT2 CSNIN CSPOUT MASTER V CHARGING CURRENT = 30A BAT2 LD033 94 CSNOUT CSPIN 10 12 14 16 V EXTV LT8708* INCHIP CC V (V) BAT1 SHDN VOUTLOMON LD033 87081 TA01b SWEN SWEN INTV CC LT8708-1 RVSOFF RVSOFF SLAVE CLKOUT SYNC GATEV CC ICP ICP *REFER TO LT8708 DATA ICN ICN DIR IMON OP SHEET FOR VINHIMON IMON ON MASTER SETUP DB1 DB2 IMON INP DIR IMON INN RVS (0V) FWD (3V) TO TO FBIN LD033 MODE V RT SS CLKOUT FBOUT C BOOST1 BOOST2 POWER TRANSFER LD033 DECISION LOGIC 120kHz 87081 TA01a Rev A 1 Document Feedback For more information www.analog.com EFFICIENCY (%)LT8708-1 TABLE OF CONTENTS Features ..................................................... 1 Current Monitoring and Limiting .............................21 Applications ................................................ 1 Monitoring: I OUT(SLAVE) .................................................... 21 Typical Application ........................................ 1 Monitoring and Limiting: I ......................21 IN(SLAVE) Description.................................................. 1 Multiphase Clocking ...............................................22 Absolute Maximum Ratings .............................. 3 Applications Information ................................ 23 Pin Configuration .......................................... 3 Quick-Start Multiphase Setup .................................23 Order Information .......................................... 4 Quick Setup: Design the Master Phase .................23 Electrical Characteristics ................................. 4 Quick Setup: Design the Slave Phase(s) ...............23 Typical Performance Characteristics ................... 8 Quick Setup: Evaluation ........................................23 Pin Functions .............................................. 10 Choosing the Total Number of Phases ....................23 Block Diagram ............................................. 13 Operating Frequency Selection ............................... 24 Operation................................................... 14 C and C Selection ........................................... 24 IN OUT Common LT8708-1 and LT8708 Features ............... 14 C and C Selection: V Capacitance .............. 24 IN OUT IN Adding Phases to an LT8708 Application ................ 14 C and C Selection: V Capacitance ...........25 IN OUT OUT Adding Phases: The Master LT8708 .................... 14 VINHIMON, VOUTLOMON and RVSOFF .................25 Adding Phases: The Slave LT8708-1 .................... 16 Configuring the I Current Limits ................26 IN(SLAVE) Start-Up .................................................................. 17 Regulating I OUT(SLAVE) ........................................................26 Start-Up: SWEN Pin .............................................. 17 I : Circuit Description .............................26 OUT(SLAVE) Start-Up: Soft-Start of Switching Regulator ......... 18 I : Configuration ....................................28 OUT(SLAVE) Control Overview .................................................... 18 Loop Compensation ................................................28 Power Switch Control ............................................ 19 Voltage Lockouts ....................................................29 Unidirectional and Bidirectional Conduction ........... 19 Circuit Board Layout Checklist ...............................29 Error Amplifiers ...................................................... 19 Design Example .....................................................29 Transfer Function: I vs I Typical Applications ...................................... 31 OUT(SLAVE) OUT(MASTER) ..........20 Transfer Function: CCM ........................................21 Package Description ..................................... 35 Transfer Function: DCM, HCM and Burst Mode Revision History .......................................... 37 Operation ................................................................21 Typical Application ....................................... 38 Related Parts .............................................. 38 Rev A 2 For more information www.analog.com