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80V Synchronous 4-Switch Buck-Boost DC/DC
Controller with Flexible Bidirectional Capability
FEATURES
Single Inductor Allows V
n
Equal to V
OUT
Six Independent Forms of Regulation
n
V
Current (Forward and Reverse)
n
IN
V
Current (Forward and Reverse)
n
OUT
V
and V
Voltage
n
IN
OUT
Forward and Reverse Discontinuous Conduction
n
Mode Supported
Supports MODE and DIR Pin Changes While Switching
n
V
Range 2.8V (Need EXTV
n
INCHIP
V
Range: 1.3V to 80V
n
OUT
Synchronous Rectification: Up to 99% Efficiency
n
Available in 40-Lead (5mm × 8mm) QFN with High
n
Voltage Pin Spacing
APPLICATIONS
High Voltage Buck-Boost Converters
n
Bidirectional Charging System
n
Automotive 48V Systems
n
TYPICAL APPLICATION
12V Bidirectional Dual Battery System with FHCM and RHCM
I
LIM
V
BAT1
+
+
10V
TO 16V
BATTERY
–
POWER TRANSFER
DECISION LOGIC
RVS (0V)
FWD (3V)
LD033
Document Feedback
Above, Below, or
IN
> 6.4V) to 80V
CC
TO DIODE
TO DIODE
D
D
B1
B2
TG1 BOOST1 SW1 BG1 CSP CSN
GND BG2 SW2 BOOST2 TG2
CSNIN
CSPOUT
CSNOUT
CSPIN
EXTV
V
INCHIP
VOUTLOMON
SHDN
FBIN
LT8708
VINHIMON
GATEV
IMON_OP
DIR
IMON_ON
SWEN
LDO33
IMON_INP
RVSOFF
IMON_INN
V
MODE
RT
SS
SYNC
CLKOUT
C
126kHz
For more information
DESCRIPTION
The
LT
8708
is a high performance buck-boost switching
®
regulator controller that operates from an input voltage
that can be above, below or equal to the output voltage.
Features are included to simplify bidirectional power
conversion in battery/capacitor backup systems and other
applications that may need regulation of V
and/or I
. Forward and reverse current can be monitored
IN
and limited for the input and output sides of the converter.
All four current limits (forward input, reverse input, forward
output and reverse output) can be set independently using
four resistors on the PCB.
The MODE pin can select between discontinuous conduc-
tion mode (DCM), continuous conduction mode (CCM),
hybrid conduction mode (HCM) and Burst Mode
In combination with the DIR (direction) pin, the chip can be
configured to process power only from V
from V
to V
OUT
IN
to 80V output range, the LT8708 is compatible with most
solar, automotive, telecom and battery-powered systems.
All registered trademarks and trademarks are the property of their respective owners.
I
LIM
CC
FBOUT
INTV
CC
CC
ICN
ICP
D
B1
TO
8708 TA01a
BOOST1
BOOST2
www.analog.com
IN
. With a wide 2.8V to 80V input and 1.3V
V
BAT2
+
Efficiency
+
10V
EFFICIENCY
TO 16V
BATTERY
–
100
99
98
97
96
95
D
B2
94
TO
10
12
LT8708
, V
, I
,
OUT
IN
OUT
operation.
®
to V
or only
OUT
V
= 13.5V
BAT2
I
= 15A
OUT
14
16
V
(V)
BAT1
8708 TA01b
Rev 0
1
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Table of Contents
Related Manuals for Linear Technology Analog Devices LT8708
Summary of Contents for Linear Technology Analog Devices LT8708
-
Page 1: Features
LT8708 80V Synchronous 4-Switch Buck-Boost DC/DC Controller with Flexible Bidirectional Capability FEATURES DESCRIPTION Single Inductor Allows V Above, Below, or 8708 is a high performance buck-boost switching ® Equal to V regulator controller that operates from an input voltage Six Independent Forms of Regulation that can be above, below or equal to the output voltage. -
Page 2: Table Of Contents
LT8708 TABLE OF CONTENTS Features ............. 1 Applications Information ........ 26 Applications ..........1 Verify the Power Flow Conditions ......26 Typical Application ........1 Operating Frequency Selection .......26 Description..........1 Internal Oscillator ........... 27 Absolute Maximum Ratings ......3 SYNC Pin and Clock Synchronization ..... 27 Order Information .......... -
Page 3: Absolute Maximum Ratings
LT8708 ABSOLUTE MAXIMUM RATINGS PIN CONFIGURATION (Note 1) – V – V CSPIN CSNIN TOP VIEW – V ....... –0.3V to 0.3V CSPOUT CSNOUT CSP, CSN Voltage ......... –0.3V to 3V Voltage (Note 2) ........–0.3V to 2.2V 40 39 38 37 36 35 RT, FBOUT, SS Voltage ........ -
Page 4: Electrical Characteristics
LT8708 ELECTRICAL CHARACTERISTICS denotes the specifications which apply over the full operating 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 ELECTRICAL CHARACTERISTICS denotes the specifications which apply over the full operating 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 SWEN Internal Pull-Down Release Voltage SHDN = 3V 0.75 MODE Pin Continuous Conduction Mode (CCM)
- Page 6 LT8708 ELECTRICAL CHARACTERISTICS denotes the specifications which apply over the full operating 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 Line Regulation for IMON_INP, IMON_INN, IMON_OP = 12V to 80V 0.002 0.005...
- Page 7 LT8708 ELECTRICAL CHARACTERISTICS denotes the specifications which apply over the full operating 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 IMON_OP, IMON_ON, ICP and ICN Max μA Output Current IMON_OP Error Amp EA6 g...
- Page 8 LT8708 ELECTRICAL CHARACTERISTICS denotes the specifications which apply over the full operating temperature range, otherwise specifications are at T = 25°C. V = 12V, SHDN = 3V, DIR = 3V unless otherwise noted (Note 3). INCHIP PARAMETER CONDITIONS UNITS CLKOUT Rise Time = 200pF LOAD CLKOUT Fall Time...
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Page 9: Typical Performance Characteristics
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) = 38V = 48V = 51.5V = 47.4V = 47.4V = 47.4V 0.01 0.01... - Page 10 LT8708 TYPICAL PERFORMANCE CHARACTERISTICS Minimum Inductor Current Sense INTV Line Regulation Minimum Inductor Current Sense Voltage vs Duty Cycle (EXTV = 0V) Voltage at Minimum Duty Cycle –20 –20 –40 –40 BUCK REGION –60 –60 –80 BUCK REGION –80 –100 –100 –120 BOOST REGION...
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Page 11: Typical Performance Characteristics
LT8708 TYPICAL PERFORMANCE CHARACTERISTICS SHDN and SWEN Pin Thresholds SHDN Pin Current vs Temperature 1.30 1.28 1.26 1.24 RISING 1.22 1.20 1.18 FALLING 1.16 1.14 SHDN 1.12 SWEN 1.10 –45 –20 105 130 155 12 15 18 21 24 27 30 TEMPERATURE (°C) SHDN PIN VOLTAGE (V) 8708 G20... - Page 12 LT8708 TYPICAL PERFORMANCE CHARACTERISTICS Discontinuous Mode (Page 59) Continuous Mode (Page 59) Continuous Mode (Page 59) 20V/DIV 20V/DIV 20V/DIV 20V/DIV 20V/DIV 20V/DIV 5A/DIV 5A/DIV 5A/DIV 5 s/DIV 5 s/DIV 5 s/DIV 8708 G24 8708 G25 8708 G26 = 38V = 48V = 52V = 47.4V = 47.4V...
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Page 13: Pin Functions
LT8708 PIN FUNCTIONS CLKOUT (Pin 1): Clock Output Pin. Use this pin to syn- IMON_INP (Pin 11): Positive V Current Monitor and chronize one or more compatible switching regulator ICs Limit Pin. The current out of this pin is 20μA plus a current to the LT8708. - Page 14 LT8708 PIN FUNCTIONS RVSOFF (Pin 25): Reverse Conduction Disable Pin. This CSPIN (Pin 33): The (+) Input to the V Current Monitor is an input/output open-drain pin that requires a pull up Amplifier. Connect this pin to V when not in use. See resistor.
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Page 15: Block Diagram
LT8708 BLOCK DIAGRAM SENSE1 SENSE 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 RVSOFF RVSOFF LDO33 – HIMON1 LDO33 VINHIMON HIMON3 1.207V HIMON2 VOUTLOMON... -
Page 16: Operation
LT8708 OPERATION TYPOGRAPHICAL CONVENTIONS Refer to the Block Diagram (Figure 1) when reading the following sections about the operation of the LT8708. The LT8708 is a high performance 4-switch buck-boost controller that includes features to facilitate bidirectional START-UP current and power flow. Using the LT8708, an application can command power to be delivered from V to V Figure 2 illustrates the start-up sequence for the LT8708. -
Page 17: Start-Up: Soft-Start Of Switching Regulator
LT8708 OPERATION < 160°C AND SHDN > 1.221V AND V > 2.5V AND SHDN < 1.181V OR JUNCTION INCHIP ((INTV AND GATEV < 4.65V) < 2.5V OR INCHIP OR LDO33 < 3.04V) > 165°C JUNCTION CHIP OFF SWITCHER OFF 1 •... -
Page 18: Power Switch Control
LT8708 OPERATION can be used to limit or regulate their respective voltages or with constant current (EA6) to a maximum voltage (EA4) currents as shown in Table 1. and also reversed, at times, to supply power back to V using the other error amplifiers to regulate V and limit Table 1. -
Page 19: Switch Control: Buck Region (Vin >> Vout )
LT8708 OPERATION When V is much higher than V , the duty cycle of Switch Control: Buck Region (V >> V switch M2 will increase, causing the M2 switch off-time When V is significantly higher than V , the part will run to decrease. -
Page 20: Switch Control: Boost Region
LT8708 OPERATION turns off and M2 turns on. The LT8708 then operates as CLOCK if in buck mode until A5 trips. Finally, switch M2 turns off SWITCH M1 and M1 turns on until the end of the cycle. SWITCH M2 Switch Control: Boost Region (V <<... -
Page 21: Bidirectional Conduction: Ccm
LT8708 OPERATION The conduction configuration can be changed during modes (DCM: discontinuous conduction mode, HCM: hy- brid current mode and Burst Mode operation) only allow operation, as needed, with the following restrictions: current and power to flow in one direction. Unidirectional 1. -
Page 22: Unidirectional Conduction: Hcm
LT8708 OPERATION increases the power flowing from V into V . Higher allowing M4 (or M1) to turn on and reduce the diode’s voltage reduces or stops the flow. power dissipation. Forward (or reverse) DCM affects the power switches NOTE: In FHCM operation connect a 17.4k resistor from as follows. -
Page 23: Vout Regulation And Sensing
LT8708 OPERATION : Regulation Table 4. Automatically Disabled Error Amp Conditions RDCM or RHCM is regulated, subject to the priorities in Table 3, us- ing a resistor divider between V , FBOUT and ground. ERROR VOUTLOMON VINHIMON RVSOFF PIN NAME ASSERTED ASSERTED –... -
Page 24: Vin Regulation And Sensing
LT8708 OPERATION REGULATION AND SENSING A resistor divider between V , VINHIMON and ground is used to detect V overvoltage. This function prevents Two pins, FBIN and VINHIMON, are provided to sense reverse conduction, from V to V , from forcing V the V voltage and issue the appropriate response to the higher than desired. -
Page 25: Monitoring: Icp And Icn Pins
LT8708 OPERATION INTV /EXTV /GATEV /LDO33 POWER The I and I currents can be limited and regulated to independent maximum positive values. When I causes Power for the top and bottom MOSFET drivers, the LDO33 IMON_INP to rise near or above 1.209V (typical), EA5 pin and most internal circuitry is derived from the INTV typically causes V to pull down and limit/regulate the... -
Page 26: Applications Information
LT8708 APPLICATIONS INFORMATION This Applications Information section provides additional Table 6. Power Flow Verification Table details for setting up an application using the LT8708. Top- 6(a) ics include verifying the power flow conditions, selection > < & > of various external components including the switching OUT_VOUTLOMON <... -
Page 27: Internal Oscillator
LT8708 APPLICATIONS INFORMATION INTERNAL OSCILLATOR CLKOUT PIN AND CLOCK SYNCHRONIZATION The operating frequency of the LT8708 can be set using The CLKOUT pin can drive up to 200pF and toggles the internal free-running oscillator. When the SYNC pin at the LT8708’s internal clock frequency whether the is driven low (<... -
Page 28: Rsense Selection And Maximum Current
LT8708 APPLICATIONS INFORMATION For example, an application with a V range of 12V to inductor current in the buck region. For example, refer to 48V and V set to 36V will have: the Maximum Inductor Current Sense Voltage vs Duty Cycle graph in the Typical Performance Characteristics section. - Page 29 LT8708 APPLICATIONS INFORMATION Otherwise, if the inductance is already known then duty cycle. See Switch Control: Boost Region (V << ∆I can be more accurately calculated as ) section for the equation to calculate the minimum L(MAX,BOOST,FWD) follows: duty cycle DC (ABSMIN, M3, BOOST) Before calculating the maximum R resistance allowed...
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Page 30: Rsense Selection: Max Rsense
LT8708 APPLICATIONS INFORMATION where: where: is the minimum duty cycle per- is the minimum inductor cur- (ABSMIN,M2,BUCK) RSENSE(MIN,BOOST,MINDC) centage in the buck region as calculated previously rent sense voltage in the boost region at the minimum duty cycle. Typical value is –93mV. ƒ... - Page 31 LT8708 APPLICATIONS INFORMATION where: Next, the inductor ripple current in the buck region must be determined. If the main inductor L is not known, the is the minimum inductor RSENSE(MIN,BUCK,MAXDC) maximum ripple current ∆I can be estimated L(MAX,BUCK) current sense voltage at the maximum duty cycle. by choosing ∆I to be 30% to 50% of the maxi- L(MAX,BUCK)
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Page 32: Rsense Filtering
LT8708 APPLICATIONS INFORMATION INDUCTOR (L) SELECTION 1.00 For high efficiency, choose an inductor with low core loss, 0.80 such as ferrite. Also, the inductor should have low DC MAXIMUM resistance to reduce the I R losses, and must be able to 0.60 INDUCTOR CURRENT... -
Page 33: L Selection: Subharmonic Oscillations
LT8708 APPLICATIONS INFORMATION To provide adequate reverse I current at low V volt- In the boost region, if V can be greater than twice V ages in the buck region, L should be at least: calculate L as follows: (MIN2,BOOST) ≅... -
Page 34: Power Mosfet Selection
LT8708 APPLICATIONS INFORMATION The maximum reverse inductor current when operating The maximum reverse inductor current in the boost region in the buck region is: for applications in which V ≥ 2•V OUT(MAX) IN(MAX) ≅ I IN(MAX,BUCK) L(MAX,BOOST,RVS) IN(MAX,RVS) ≅ I •... - Page 35 LT8708 APPLICATIONS INFORMATION It is very important to consider power dissipation when SW2 node capacitance, which is dominated by the out- selecting power MOSFETs. The most efficient circuit will put capacitance of the external MOSFETs. Use Table 7 to use MOSFETs that dissipate the least amount of power. determine which power components are applicable in the Power dissipation must be limited to avoid overheating various regions of operation.
- Page 36 LT8708 APPLICATIONS INFORMATION Switching Component Equations for M1 and M2: Switch M1: For positive conduction, the maximum power dissipation in M1 occurs either in the buck region when or P SW[M1,BUCK] SW[M2,BUCK] is highest, V is highest, and switching power losses ≅...
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Page 37: Cin And Cout Selection
LT8708 APPLICATIONS INFORMATION Gate Resistors: In some cases it can be beneficial to add polymer, aluminum electrolytic and ceramic capacitors are 1Ω to 10Ω of resistance between some of the NMOS gate all available in surface mount packages. Capacitors with pins and their respective gate driver pins on the LT8708 low ESR and high ripple current ratings, such as OS-CON (i.e., TG1, BG1, TG2, BG2). -
Page 38: Schottky Diode (D1, D2, D3, D4) Selection
LT8708 APPLICATIONS INFORMATION When low ESR ceramic capacitance is added in parallel With enough ceramic caps added in parallel, the steady with the bulk capacitor, the V ripple is approximately: state V ripple due to charging and discharging the ceramic C is given by the following equations: ∆V ≅... -
Page 39: Topside Mosfet Driver Supply (C )
LT8708 APPLICATIONS INFORMATION Because of this function, CSPIN and CSNIN should be For applications with high input or output voltages connected across R in series with the M1 drain. (typically >40V) avoid Schottky diodes with excessive SENSE1 Connect both pins to the M1 drain if they are not being reverse-leakage currents, particularly at high tempera- used. - Page 40 LT8708 APPLICATIONS INFORMATION 1. Connect a resistor divider between V , VINHIMON The purpose of the VINHIMON and VOUTLOMON func- and GND to configure the V overvoltage threshold. tions becomes clearer when considering the priorities of Connect a resistor divider between V , VOUTLO- the error amplifiers (see Table 3).
- Page 41 LT8708 APPLICATIONS INFORMATION 2. Connect a resistor divider between V , FBIN, VIN- HIMON and GND to configure the V regulation and HIMON1 overvoltage thresholds (see Figure 13). Connect a LT8708 HIMON3 resistor divider between V VOUTLOMON, FBOUT VINHIMON OUT, and GND to configure the V regulation and under- HIMON2...
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Page 42: Iin And Iout Current Monitoring And Limiting
LT8708 APPLICATIONS INFORMATION and V – are the rising and falling V over- OVIN + OVIN SENSE1 FROM voltage thresholds. SYSTEM CONTROLLER and V – are the rising and falling V UVOUT + UVOUT CSPIN CSNIN undervoltage thresholds. LT8708 – = 1m and R are shown in Figure 13 and Figure 14. - Page 43 LT8708 APPLICATIONS INFORMATION Transconductance amplifier A3 performs this monitoring Current Limiting: As shown in Figure 15, IMON_INP voltage function. A3 converts the current sense voltage, V that exceeds 1.209V (typical) causes V to reduce, thus CSPIN- , into two currents: limiting the forward I and inductor currents.
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Page 44: Loop Compensation
LT8708 APPLICATIONS INFORMATION this way, ICP and ICN can be used to monitor the I sense amplifier outputs may clip at the –20μA limits when current in the forward and reverse directions respectively the average sensed current is low but contains high AC (see the Current Monitoring, Regulation and Limiting: ICP content. -
Page 45: Intv Cc Regulators And Extv Cc Connection
LT8708 APPLICATIONS INFORMATION when IMON_INP and IMON_INN, respectively, are used The following list summarizes the three possible connec- to operate the LT8708 at constant current limit. tions for EXTV 1. EXTV left open (or grounded). This will cause INTV INTV REGULATORS AND EXTV CONNECTION to be powered from V... -
Page 46: Voltage Lockouts
LT8708 APPLICATIONS INFORMATION regulator is INTV . Therefore INTV must have sufficient falling thresholds of 1.221V and 1.181V, respectively. The voltage, typically > 4.0V, to properly regulate LDO33. The falling threshold for turning-off switching activity can be LDO33 and INTV regulators are enabled by the SHDN chosen using: pin and are not affected by SWEN. -
Page 47: Thermal Shutdown
LT8708 APPLICATIONS INFORMATION from a high efficiency source, such as the output or where DC is the CLKOUT duty cycle in % and T CLKOUT alternate supply if available. Also, lower capacitance is the die junction temperature in °C. The actual die tem- MOSFETs can reduce INTV current and power loss. - Page 48 LT8708 APPLICATIONS INFORMATION SENSE LT8708 SENSE LT8708 8708 F18 18(b) 18(a) Figure 18. Switches Layout • Avoid running signal traces parallel to the traces that • Minimize inductance from the sources of M2 and M3 carry high di/dt current because they can receive to R by making the trace short and wide.
-
Page 49: Hot Plugging Considerations
LT8708 APPLICATIONS INFORMATION spacing. Avoid having sense lines pass through noisy multi-pin connector. Alternatively, consider the use of a areas, such as switch nodes. The optional filter network Hot Swap controller such as the LT1641, LT4256, etc. to capacitor between CSP and CSN should be as close make a current limited connection. - Page 50 LT8708 APPLICATIONS INFORMATION ≅ 93mV Verify expected operation by combining Table 6(a) and RSENSE(MIN,BOOST,MINDC) Table 6(b): Next, estimate the inductor current ripples at maximum and minimum boost duty cycles: • When V < V (12V) and V > V (12V) IN_FBIN OUT_FBOUT ∆I...
- Page 51 LT8708 APPLICATIONS INFORMATION ∆I ≅ SENSE(MAX,BOOST,FWD) L(MIN,BUCK) 2 • V • V OUT(MAX,FWD) RSENSE(MAX,BOOST,MAXDC) IN(MIN,BOOST) Ω 2 • I • V + ∆I • V 100% 100% OUT(MAX,FWD) OUT(MAX,BOOST) L(MAX,BOOST) IN(MIN,BOOST) – 0.5 – 0.5 ...
- Page 52 LT8708 APPLICATIONS INFORMATION Inductor Selection: With R known, we can now Select M1 and M2: With 25V maximum input voltage, MOS- SENSE determine the minimum inductor value that will provide FETs with a rating of at least 30V are used. As we do not yet adequate load current in the boost region using: know the actual thermal resistance (circuit board design and airflow have a major impact) we assume that the MOSFET...
- Page 53 LT8708 APPLICATIONS INFORMATION Select M3 and M4: With 12V output voltage we need ≅ P I 2 R SWITCHING MOSFETs with 20V or higher rating. ⎛ ⎞ – V ⎜ ⎟ • I • R • ρ The highest dissipation of M3 and M4 occurs in the boost ≅...
- Page 54 LT8708 APPLICATIONS INFORMATION Voltage: Input voltage is 12V. Select R as 20k. ≅ P FBIN2 I 2 R SWITCHING FBIN1 ⎡ ⎤ = (1– DC ) • I • R • ρ ⎣ ⎢ ⎦ ⎥ (ABSMIN,M3,BOOST) IN(MAX,RVS) DS(ON) τ ⎛...
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Page 55: Typical Applications
LT8708 TYPICAL APPLICATIONS Rev 0 For more information www.analog.com... - Page 56 LT8708 APPLICATIONS INFORMATION 12V Bidirectional Dual Battery System with FHCM & RHCM Details Charge Voltage = 14.6V (FBIN in RHCM) to Stop Discharging = 10.5V (VOUTLOMON Falling) or 11.7V (VOUTLOMON Rising) BAT1 BAT2_UV Charge Voltage = 14.5V (FBOUT in FHCM) Charging Current Limit = 15A (IMON_INN) BAT2 BAT1...
- Page 57 LT8708 APPLICATIONS INFORMATION Rev 0 For more information www.analog.com...
- Page 58 LT8708 APPLICATIONS INFORMATION 48V to 14V Bidirectional Dual Battery System with FHCM & RHCM Details Charge Voltage = 48V (FBIN in RHCM) to Stop Discharging = 10.5V (VOUTLOMON Falling) or 12.3V (VOUTLOMON Rising) BAT1 BAT2_UV Charge Voltage = 14.5V (FBOUT in FHCM) Charging Current Limit = 4A (IMON_INN) BAT2 BAT1...
- Page 59 LT8708 APPLICATIONS INFORMATION Rev 0 For more information www.analog.com...
- Page 60 LT8708 APPLICATIONS INFORMATION 52V Battery Backup Supply Using FHCM and RHCM Detail Charge Voltage = 52.1V (FBOUT in FHCM) Rising to Activate V Charging = 50.2V (VINHIMON Rising Activating FHCM) LOAD Regulation Voltage = 47.4V (FBIN in RHCM) Falling to Activate Backup Operation = 45.9V (VINHIMON Falling Activating RHCM) LOAD LOAD = 36V (Falling) or 37.5V (Rising)
- Page 61 LT8708 APPLICATIONS INFORMATION Rev 0 For more information www.analog.com...
- Page 62 LT8708 APPLICATIONS INFORMATION Supercapacitor Backup Supply Using CCM Detail Charge Voltage = 15V (FBOUT) Overvoltage Rising Threshold in Backup Operation = 13.3V (VINHIMON Rising) BACKUP Regulation Voltage = 11V (FBIN) Overvoltage Falling Threshold in Backup Operation = 12.9V (VINHIMON Falling) BACKUP BACKUP = 5.42V (Falling) or 5.65V (Rising)
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Page 63: Package Description
LT8708 PACKAGE DESCRIPTION UHG Package 40-Lead Plastic QFN (5mm × 8mm) (Reference LTC DWG # 05-08-1528 Rev Ø) 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 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 1.00 TYP... -
Page 64: Typical Application
LT8708 TYPICAL APPLICATION Supercapacitor Backup Supply Using CCM TO LOADS (REGULATE TO 11V WHEN IN BACKUP) 25mΩ 2.2 H 25mΩ OUT1 OUT2 10Ω TO DIODE TO DIODE 1µF 1.2k ×6 ×6 2Ω 5mΩ 2Ω 162k 71.5k 0.22µF 0.22µF 10Ω 1µF 100Ω...
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