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80V Synchronous 4-Switch Buck-Boost DC/DC
Slave Controller for LT8708 Multiphase System
FEATURES
Slave Chip of LT8708 to Deliver Additional Power
n
Good Current Matching to the Average Output
n
Current of LT8708 Through Current Regulation
Easily Paralleled with LT8708 Through Four Pins
n
Synchronized Start-Up with LT8708
n
Same Conduction Modes as LT8708
n
Synchronous Rectification: Up to 98% Efficiency
n
Frequency Range: 100kHz to 400kHz
n
Available in 40-Lead (5mm × 8mm) QFN with High
n
Voltage Pin Spacing
APPLICATIONS
High Voltage Buck-Boost Converters
n
Bidirectional Charging Systems
n
Automotive 48V Systems
n
All registered trademarks and trademarks are the property of their respective owners.
TYPICAL APPLICATION
The LT8708-1 Two-Phase 12V Bidirectional Dual Battery System with FHCM and RHCM
V
BAT1
10V TO 16V
BATTERY
MASTER
LD033
LT8708*
SWEN
RVSOFF
CLKOUT
ICP
*REFER TO
ICN
LT8708 DATA
DIR
SHEET FOR
MASTER SETUP
RVS (0V)
FWD (3V)
POWER TRANSFER
DECISION LOGIC
Document Feedback
TO DIODE
DB1
TG1 BOOST1 SW1 BG1 CSP CSN
GND BG2 SW2 BOOST2 TG2
CSNIN
CSPIN
V
INCHIP
SHDN
SWEN
LT8708-1
RVSOFF
SLAVE
SYNC
ICP
ICN
VINHIMON
DIR
FBIN
LD033
MODE
V
RT
SS
C
LD033
For more information
DESCRIPTION
The
LT
8708-1
is a high performance buck-boost
®
switching regulator controller that is paralleled with the
LT8708 to add power and phases to an LT8708 system.
The LT8708-1 always operates as a slave to the master
LT8708 and has the capability of delivering as much cur-
rent or power as the master. One or more slaves can be
connected to a single master, proportionally increasing
power and current capability of the system.
The LT8708-1 has the same conduction modes as LT8708,
allowing the LT8708-1 to conduct current and power in
the same direction(s) as the master. The master controls
the overall current and voltage limits for an LT8708 mul-
tiphase system, and the slaves comply with these limits.
LT8708-1s can be easily paralleled with the LT8708 by
connecting four signals together. Two additional current
limits (forward V
current and reverse V
IN
available on each slave that can be set independently.
V
BAT2
10V TO
16V
BATTERY
TO DIODE
DB2
CSPOUT
CSNOUT
EXTV
CC
VOUTLOMON
LD033
INTV
CC
GATEV
CC
IMON_OP
IMON_ON
IMON_INP
IMON_INN
CLKOUT
FBOUT
120kHz
www.analog.com
LT8708-1
current) are
IN
Efficiency
Efficiency
100
99
98
97
96
95
V
BAT2
V
CHARGING CURRENT = 30A
BAT2
94
10
12
14
V
(V)
BAT1
DB1
DB2
TO
TO
BOOST1
BOOST2
87081 TA01a
= 13.5V
16
87081 TA01b
Rev 0
1
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Table of Contents
Related Manuals for Linear Technology Analog Devices LT8708-1
Summary of Contents for Linear Technology Analog Devices LT8708-1
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Page 1: Features
LT8708-1 80V Synchronous 4-Switch Buck-Boost DC/DC Slave Controller for LT8708 Multiphase System FEATURES DESCRIPTION Slave Chip of LT8708 to Deliver Additional Power 8708-1 is a high performance buck-boost ® 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. -
Page 2: Table Of Contents
LT8708-1 TABLE OF CONTENTS Features ............. 1 Current Monitoring and Limiting ......21 Applications ..........1 Monitoring: I ......... 21 OUT(SLAVE) Typical Application ........1 Monitoring and Limiting: I ...... 21 IN(SLAVE) Description..........1 Multiphase Clocking ..........22 Absolute Maximum Ratings ......3 Applications Information ........ -
Page 3: Absolute Maximum Ratings
LT8708-1 ABSOLUTE MAXIMUM RATINGS PIN CONFIGURATION (Note 1) – V – V CSPIN CSNIN – V ....... –0.3V to 0.3V CSPOUT CSNOUT TOP VIEW CSP, CSN Voltage ......... –0.3V to 3V Voltage (Note 2) ........–0.3V to 2.2V RT, FBOUT, SS Voltage ........ –0.3V to 5V 40 39 38 37 36 35 IMON_INP, IMON_INN, IMON_OP, CLKOUT... -
Page 4: Electrical Characteristics
LT8708-1 ELECTRICAL CHARACTERISTICS denotes the specifications which apply over the specified operating junction temperature range, otherwise specifications are at T = 25°C. V =12V, SHDN = 3V, DIR = 3.3V unless otherwise noted. (Note 3). INCHIP PARAMETER CONDITIONS UNITS Voltage Supplies and Regulators Operating Voltage Range EXTV = 0V... - Page 5 LT8708-1 ELECTRICAL CHARACTERISTICS denotes the specifications which apply over the specified operating junction temperature range, otherwise specifications are at T = 25°C. V =12V, SHDN = 3V, DIR = 3.3V unless otherwise noted. (Note 3). INCHIP PARAMETER CONDITIONS UNITS MODE Pin Continuous Conduction Mode (CCM) Threshold MODE Pin Hybrid DCM/CCM Mode (HCM) Range MODE Pin Discontinuous Conduction Mode (DCM) Range MODE Pin Burst Mode Operation Threshold...
- Page 6 LT8708-1 ELECTRICAL CHARACTERISTICS denotes the specifications which apply over the specified operating junction temperature range, otherwise specifications are at T = 25°C. V =12V, SHDN = 3V, DIR = 3.3V unless otherwise noted. (Note 3). INCHIP PARAMETER CONDITIONS UNITS Current Regulation Loops (Refer to Block Diagram to Locate Amplifiers) Regulation Voltages for IMON_INP and IMON_OP = 1.2V 1.185 1.209 1.231...
- Page 7 LT8708-1 ELECTRICAL CHARACTERISTICS denotes the specifications which apply over the specified operating junction temperature range, otherwise specifications are at T = 25°C. V =12V, SHDN = 3V, DIR = 3.3V unless otherwise noted. (Note 3). INCHIP PARAMETER CONDITIONS UNITS NMOS Gate Drivers TG1, TG2 Rise Time = 3300pF (Note 4) LOAD...
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Page 8: Typical Performance Characteristics
LT8708-1 TYPICAL PERFORMANCE CHARACTERISTICS = 25°C, unless otherwise noted. Efficiency vs Output Current Efficiency vs Output Current Efficiency vs Output Current (Boost Region – Page 32) (Buck Region – Page 32) (Buck-Boost Region – Page 32) = 11.5V = 16V = 14.5V = 14.5V = 12V... - Page 9 LT8708-1 TYPICAL PERFORMANCE CHARACTERISTICS = 25°C, unless otherwise noted. Load Step (Page 32) V = 12V Load Step (Page 32) V = 14.5V = 14.5V = 14.5V LT8708 I LT8708 I 10A/DIV 10A/DIV LT8708-1 I LT8708-1 I 10A/DIV 10A/DIV 500 s/DIV 500 s/DIV 87081 G10 87081 G11...
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Page 10: Pin Functions
LT8708-1 PIN FUNCTIONS CLKOUT (Pin 1): Clock Output Pin. Use this pin to syn- FBOUT (Pin 9): V Feedback Pin. This pin is connected chronize one or more compatible switching regulator ICs. to the input of error amplifier EA4. Typically, connect this CLKOUT toggles at the same frequency as the internal pin to GND to disable the EA4. - Page 11 LT8708-1 PIN FUNCTIONS CSPOUT (Pin 30): The (+) Input to the V Current BOOST1, BOOST2 (Pin 24, Pin 19): Boosted Floating Driver Supply. The (+) terminal of the bootstrap capacitor Monitor Amplifier. This pin and the CSNOUT pin measure connects here. The BOOST1 pin swings from a diode volt- the voltage across the sense resistor, R , to provide SENSE2...
- Page 12 LT8708-1 PIN FUNCTIONS MODE (Pin 37): Conduction Mode Select Pin. The voltage IMON_ON (Pin 39): Negative V Current Monitor Pin. The current out of this pin is 20µA plus a current pro- applied to this pin sets the conduction mode of the con- troller.
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Page 13: Block Diagram
LT8708-1 BLOCK DIAGRAM TO LT8708’s V SENSE1 SENSE TO LT8708’s SWEN SWEN BOOST1 CSNIN – (OPT) – CSPIN – GATEV (OPT) – INCHIP CONTROL IMON_INN STATE LOGIC IMON_INP BOOST CAPACITOR CHARGE CONTROL LDO33 CLKOUT (OPT) (OPT) SYNC BOOST2 LT8708’s CLKOUT RVSOFF TO LT8708’s TO LT8708’s V... -
Page 14: Operation
LT8708-1 OPERATION The LT8708-1 is a high performance 4-switch buck-boost Table 1. LT8708 Data Sheet Sections that Apply to the LT8708-1 slave controller that is paralleled with the master LT8708 ADDITIONAL INFORMATION to increase power capability. Using LT8708-1(s) with the LT8708 DATA SHEET SECTION IN THIS DATA SHEET LT8708, an application can command power to be deliv- Operation... - Page 15 LT8708-1 OPERATION IN(MASTER) OUT(MASTER) 4-SWITCH BUCK-BOOST CSNIN CSPOUT CSPIN CSNOUT FBOUT INCHIP LT8708 IMON_OP FBIN MASTER IMON_ON LD033 LD033 IMON_INP IMON_INN SWEN RVSOFF SYNC LD033 LD033 CLK1 FWD (>1.6V)/ SWEN RVSOFF RVS (<1.2) CLK2 SWEN RVSOFF SYNC IMON_OP LT8708-1 INCHIP SLAVE CSPIN CSNOUT...
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Page 16: Adding Phases: The Slave Lt8708-1
LT8708-1 OPERATION As another example, the master LT8708’s current regula- • The LT8708 and LT8708-1 employ different soft-start tion pins (IMON_INP, IMON_INN, IMON_OP, IMON_ON) mechanisms, and the SS pins ramp up differently. monitor and limit the per-phase V current and V cur- See the Start-Up: Soft-Start of Switching Regulator rent. -
Page 17: Start-Up
LT8708-1 OPERATION data sheet for more details. SWEN is internally pulled In addition, all LT8708-1s’ V and V should be con- down by the LT8708 and/or LT8708-1(s) when the respec- nected to the LT8708’s V and V , respectively. tive switching regulator is unable or not ready to operate See the Quick-Start Multiphase Setup Guidelines section (see CHIP OFF and SWITCHER OFF 1 states in Figure 3). -
Page 18: Start-Up: Soft-Start Of Switching Regulator
LT8708-1 OPERATION SWEN is used to synchronize the start-up between all switch control mechanism as the LT8708. See the Switch phases of the system. If one or more of the phases is Control: Soft-Start section of the LT8708 data sheet for unable to operate, SWEN is pulled low by those chips, more information. -
Page 19: Power Switch Control
LT8708-1 OPERATION pins together. In addition, the RVSOFF pins of all phases Table 3. Error Amplifiers (EA1–EA6) should be connected together. AMPLIFIER NAME PIN NAME USED TO LIMIT OR REGULATE Note that when operating in the forward hybrid conduction IMON_INN Negative I IN(SLAVE) mode (FHCM), the LT8708-1 operation differs slightly from FBIN... -
Page 20: Transfer Function: Iout(Slave)
LT8708-1 OPERATION A 1* to 3* indicates that the error amplifier listed for that row is disabled under that column’s condition. The pur- poses of disabling the respective amplifiers are: 1* This improves transient response when VOUTLOMON de-asserts. 2* This improves transient response when VINHIMON –20 de-asserts. -
Page 21: Transfer Function: Ccm
LT8708-1 OPERATION 3. V > 20.5mV: In this region of moder- Transfer Function: CCM (CSPOUT–CSNOUT)M ate to high current from the master, the slave delivers the Figure 5 shows the transfer function of the slave’s regu- same current as the master. lated current sense voltage (V ) vs the (CSPOUT–CSNOUT)S... -
Page 22: Multiphase Clocking
LT8708-1 OPERATION and limiting circuitry, it can be configured with redundant MULTIPHASE CLOCKING current limiting. It is recommended to set the slave input A multiphase application usually has switching regulators current limit magnitudes to be the same or higher than operating at the same frequency but at different phases to those set by the master. -
Page 23: Applications Information
LT8708-1 APPLICATIONS INFORMATION This Applications Information section provides additional Connect identical resistor divider networks on SHDN as details for setting up a multiphase application using the well as on VINHIMON and VOUTLOMON (if used). If not LT8708-1(s) and LT8708. Topics include quick multi- used, connect VINHIMON to GND and/or VOUTLOMON to phase setup guidelines, choosing the total number of the LT8708-1’s LDO33. -
Page 24: Operating Frequency Selection
LT8708-1 APPLICATIONS INFORMATION OPERATING FREQUENCY SELECTION 0.60 1-PHASE The LT8708-1 uses a constant frequency architecture 2-PHASE 0.55 3-PHASE operating between 100kHz and 400kHz. The LT8708-1 4-PHASE 0.50 6-PHASE should be synchronized to the same frequency as the 0.45 LT8708 by connecting a clock signal to the SYNC pin. 0.40 An appropriate resistor must be placed from the RT pin to ground. -
Page 25: Out Capacitance
LT8708-1 TYPICAL APPLICATIONS make sure V voltage ripple is adequately low for the 1–PHASE application. 2–PHASE 3–PHASE and C Selection: V Capacitance 4–PHASE Discontinuous V current is highest in the boost region 6–PHASE due to the M4 switch toggling on and off. Make sure that the C capacitor network has low enough ESR and is sized to handle the maximum RMS current. -
Page 26: Current Limits
LT8708-1 APPLICATIONS INFORMATION more chips’ VINHIMON or VOUTLOMON comparator is reaches input current limiting before the master, the slave triggered, the RVSOFF pin is pulled low to prevent the can no longer deliver additional current as requested by entire multiphase system from delivering reverse current the master. - Page 27 LT8708-1 TYPICAL APPLICATIONS results in higher I current and vice versa. current sense voltage of V = 4A • 10mΩ OUT(SLAVE) (CSPOUT–VCSNOUT)M is driven by error amplifier EA6 during I = 40mV. Locate 40mV along the X-axis of Figure 11. The OUT(SLAVE) regulation.
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Page 28: Iout(Slave) : Configuration
LT8708-1 APPLICATIONS INFORMATION LOOP COMPENSATION also be used to understand RDCM and RHCM operation by multiplying the V and the V (CSPOUT–CSNOUT)M (CSPOUT– To compensate a multiphase system of the LT8708 and axis values by –1. CSNOUT)S LT8708-1(s), most of the initial compensation component selection can be done by analyzing the individual voltage As mentioned previously, 17.4k resistors must be con- regulator and/or current regulator(s) independently of... -
Page 29: Voltage Lockouts
LT8708-1 TYPICAL APPLICATIONS CIRCUIT BOARD LAYOUT CHECKLIST approach that is used for compensating the LT8708’s input current regulation loops. The LT8708’s circuit board layout guidelines also apply to the LT8708-1(s). Refer to the Circuit Board Layout 3. Complete the multiphase system with the LT8708 Checklist section of the LT8708 data sheet for details. - Page 30 LT8708-1 APPLICATIONS INFORMATION MODE Pin: Connect the MODE pin to GND for CCM And the maximum slave V current in the reverse direc- operation. tion is: = 3.6A SWEN and RVSOFF Pins: Connect the SWEN and RVSOFF IN(MAX,RVS,SLAVE) IN(IMON_ON,MASTER) pins together for the LT8708 and LT8708-1, respectively. Choose R to be around 17.4k, so that the IMON_INP...
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Page 31: Typical Applications
LT8708-1 TYPICAL APPLICATIONS 2-Phase 12V Bidirectional Dual Battery System with FHCM and RHCM Rev 0 For more information www.analog.com... - Page 32 LT8708-1 TYPICAL APPLICATIONS 2-Phase 12V Bidirectional Dual Battery System with FHCM and RHCM Forward Conduction V Reverse Conduction V BAT1 BAT1 ~12V, V = ~14V, I = ~30A ~12V, V = ~14V, I = ~30A BAT2 BAT2 AND I AND I 10A/DIV 10A/DIV LT8708 SW1...
- Page 33 LT8708-1 TYPICAL APPLICATIONS 4-Phase 48V to 12V Bidirectional Dual Battery System with FHCM and RHCM Rev 0 For more information www.analog.com...
- Page 34 LT8708-1 TYPICAL APPLICATIONS 4-Phase 48V to 12V Bidirectional Dual Battery System with FHCM and RHCM Direction Change Phase 1 to 4 Inductor Current 5V/DIV PHASE 1 I 20A/DIV PHASE 1 TO PHASE 4 I PHASE 2 I 5A/DIV 20A/DIV PHASE 3 I 20A/DIV 56ms/DIV 87081 TA04b...
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Page 35: Package Description
LT8708-1 PACKAGE DESCRIPTION UHG Package 40-Lead Plastic QFN (5mm × 8mm) (Reference LTC DWG # 05-08-1528 Rev A) 0.70 ±0.05 5.50 ±0.05 5.85 ±0.10 PACKAGE 4.10 ±0.05 OUTLINE 3.50 REF 3.10 ±0.10 0.25 ±0.05 6.50 REF 7.10 ±0.05 8.50 ±0.05 RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED C 0.35... -
Page 36: Typical Application
LT8708-1 TYPICAL APPLICATION 4-Phase 48V to 12V Bidirectional Dual Battery System with FHCM and RHCM 10 H 5mΩ 2mΩ BAT1 BAT2 OUT2 OUT4 ×2 OUT3 24V TO 55V OUT1 ×2 BATTERY 10Ω TO DIODE TO DIODE – TO 16V 1Ω 1Ω...
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