LT8705 Datasheet PDF - Linear Technology

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LT8705
Linear Technology

Part Number LT8705
Description 80V VIN and VOUT Synchronous 4-Switch Buck-Boost DC/DC Controller
Page 30 Pages


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Electrical Specifications Subject to Change
LT8705
80V VIN and VOUT
Synchronous 4-Switch Buck-
Boost DC/DC Controller
FEATURES
n Single Inductor Allows VIN Above, Below, or Equal
to Regulated VOUT
n VIN Range 2.8V (Need EXTVCC > 6.4V) to 80V
n VOUT Range: 1.3V to 80V
n Quad N-Channel MOSFET Gate Drivers
n Synchronous Rectification: Up to 98% Efficiency
n Input and Output Current Monitor Pins
n Synchronizable Fixed Frequency: 100kHz to 400kHz
n Integrated Input Current, Input Voltage, Output
Current and Output Voltage Feedback Loops
n Clock Output Usable To Monitor Die Temperature
n Available in 38-Lead (5mm × 7mm) QFN and TSSOP
Packages with the TSSOP Modified for Improved
High Voltage Operation
APPLICATIONS
n High Voltage Buck-Boost Converters
n Input or Output Current Limited Converters
DESCRIPTION
The LT®8705 is a high performance buck-boost switch-
ing regulator controller that operates from input voltages
above, below or equal to the output voltage. The part has
integrated input current, input voltage, output current
and output voltage feedback loops. With a wide 2.8V to
80V input and 1.3V to 80V output range, the LT8705 is
compatible with most solar, automotive, telecom and
battery-powered systems.
The operating mode of the controller is determined
through the MODE pin. The MODE pin can select among
discontinuous mode, forced continuous mode and Burst
Mode® operation. The LT8705 also features programmable
UVLO and switching currents, along with input and output
current monitoring with programmable maximum levels.
L, LT, LTC, LTM, Linear Technology, Burst Mode, µModule and the Linear logo are registered
trademarks of Linear Technology Corporation. All other trademarks are the property of their
respective owners.
http://www.DataSheet4U.com/
TYPICAL APPLICATION
Telecom Voltage Stabilizer
VIN
36V TO
80V
1µF
+ 220µF
×2
M1
×2
4.7µF
×4
TO
DIODE
0.22µF
×2
22µH
M2
M3
×2
1nF 10Ω 10mΩ
1nF 10Ω
×2
M4
TO
DIODE
0.22µF
TG1 BOOST1 SW1 BG1 CSP
CSNIN
CSN
GND BG2 SW2 BOOST2 TG2
CSPOUT
CSPIN
CSNOUT
100k
VIN
SHDN
SWEN
LDO33
MODE
LT8705
EXTVCC
FBOUT
INTVCC
GATEVCC
SRVO_FBIN
FBIN SRVO_FBOUT
RT SRVO_IIN
71.5k
SS
SRVO_IOUT
IMON_IN
20k
4.7µF
VC
215k 56.2k
1µF 220pF
3.3nF
CLKOUT
202kHz
SYNC
IMON_OUT
4.7µF
×6
VOUT
+
48V
220µF 5A
×2
392k
10k
4.7µF
4.7µF
TO TO
BOOST1 BOOST2
Efficiency and Power Loss
100 6
5
95
4
90 3
2
85
VOUT = 48V 1
ILOAD = 2A
80 0
30 40 50 60 70 80
VIN (V)
8705 TA01b
8705 TA01
For more information www.linear.com/8705
8705p
1



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LT8705
ABSOLUTE MAXIMUM RATINGS (Note 1)
VCSP-VCSN, VCSPIN-VCSNIN,
VCSPOUT-VCSNOUT...................................... –0.3V to 0.3V
SS, CLKOUT, CSP, CSN Voltage.................... –0.3V to 3V
VC Voltage (Note 2).................................... –0.3V to 2.2V
RT, LDO33, FBOUT Voltage........................... –0.3V to 5V
IMON_IN, IMON_OUT Voltage...................... –0.3V to 5V
SYNC Voltage............................................. –0.3V to 5.5V
INTVCC, GATEVCC Voltage............................. –0.3V to 7V
VBOOST1-VSW1, VBOOST2-VSW2...................... –0.3V to 7V
SWEN, MODE Voltage................................... –0.3V to 7V
SRVO_FBIN, SRVO_FBOUT Voltage............ –0.3V to 30V
SRVO_IIN, SRVO_IOUT Voltage.................. –0.3V to 30V
FBIN, SHDN Voltage.................................... –0.3V to 30V
CSNIN, CSPIN, CSPOUT, CSNOUT Voltage...–0.3V to 80V
VIN, EXTVCC Voltage................................... –0.3V to 80V
SW1, SW2 Voltage.......................................81V (Note 7)
BOOST1, BOOST2 Voltage.......................... –0.3V to 87V
BG1, BG2, TG1, TG2............................................ (Note 6)
Operating Junction Temperature Range
LT8705E (Notes 1, 3).......................... –40°C to 125°C
LT8705I (Notes 1, 3)........................... –40°C to 125°C
Storage Temperature Range................... –65°C to 150°C
Lead Temperature (Soldering, 10 sec)
FE Package........................................................ 300°C
PIN CONFIGURATION
TOP VIEW
SHDN 1
CSN 2
CSP 3
LDO33 4
FBIN 5
FBOUT 6
IMON_OUT 7
VC 8
SS 9
CLKOUT 10
SYNC 11
RT 12
38 37 36 35 34 33 32
39
GND
13 14 15 16 17 18 19
31 CSPOUT
30 CSNOUT
29 EXTVCC
28 SRVO_FBOUT
27 SRVO_IOUT
26 SRVO_IIN
25 SRVO_FBIN
24 NC
23 BOOST1
22 TG1
21 SW1
20 NC
UHF PACKAGE
38-LEAD (5mm × 7mm) PLASTIC QFN
TJMAX = 125°C, θJA = 34°C/W
EXPOSED PAD (PIN 39) IS GND, MUST BE SOLDERED TO PCB
http://www.DataSheet4U.com/
INTVCC 1
MODE 2
IMON_IN 3
SHDN 4
CSN 5
CSP 6
LDO33 7
FBIN 8
FBOUT 9
IMON_OUT 10
VC 11
SS 12
CLKOUT 13
SYNC 14
RT 15
GND 16
BG1 17
GATEVCC 18
BG2 19
TOP VIEW
39
GND
38 VIN
37 CSPIN
36 CSNIN
34 CSPOUT
32 CSNOUT
30 EXTVCC
28 BOOST1
26 TG1
24 SW1
22 SW2
21 TG2
20 BOOST2
FE PACKAGE
VARIATION: FE38(31)
38-LEAD PLASTIC TSSOP
TJMAX = 125°C, θJA = 25°C/W
EXPOSED PAD (PIN 39) IS GND, MUST BE SOLDERED TO PCB
8705p
2 For more information www.linear.com/8705



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LT8705
ORDER INFORMATION
LEAD FREE FINISH
TAPE AND REEL
PART MARKING*
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LT8705EUHF#PBF
LT8705EUHF#TRPBF
8705
38-Lead (5mm × 7mm) Plastic QFN
–40°C to 125°C
LT8705IUHF#PBF
LT8705IUHF#TRPBF
8705
38-Lead (5mm × 7mm) Plastic QFN
–40°C to 125°C
LT8705EFE#PBF
LT8705EFE#TRPBF
LT8705FE
38-Lead Plastic TSSOP
–40°C to 125°C
LT8705IFE#PBF
LT8705IFE#TRPBF
LT8705FE
38-Lead Plastic TSSOP
–40°C to 125°C
Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.
For more information on lead free part marking, go to: http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/
E LECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VIN = 12V, SHDN = 3V unless otherwise noted. (Note 3)
PARAMETER
CONDITIONS
MIN TYP MAX
Voltage Supplies and Regulators
VIN Operating Voltage Range
VIN Quiescent Current
VIN Quiescent Current in Shutdown
EXTVCC Switchover Voltage
EXTVCC Switchover Hysteresis
INTVCC Current Limit
INTVCC Voltage
INTVCC Load Regulation
INTVCC, GATEVCC Undervoltage Lockout
INTVCC, GATEVCC Undervoltage Lockout Hysteresis
INTVCC Regulator Dropout Voltage
LDO33 Pin Voltage
EXTVCC = 0V
EXTVCC = 7.5V
Not Switching, VEXTVCC = 0
VSHDN = 0V
IINTVCC = 20mA, VEXTVCC Rising
l 5.5
l 2.8
l 6.15
2.65
0
6.4
0.18
80
80
4.2
1
6.6
Maximum Current Draw from INTVCC and LDO33
Pins Combined. Regulated from V or EXTV (12V)http://www.DataSheet4U.com/
IN CC
INTVCC = 5.25V
INTVCC = 4.5V
l
l
90
28
127 165
42 55
Regulated
Regulated
from
from
VEXINT,VIICNCTV(1CC2V=),2I0INmTAVCC
=
20mA
l 6.15 6.35 6.55
l 6.15 6.35 6.55
IINTVCC = 0mA to 50mA
–0.5 –1.5
INTVCC Falling, GATEVCC Connected to INTVCC
l 4.45 4.65 4.85
GATEVCC Connected to INTVCC
160
VIN-VINTVCC, IINTVCC = 20mA
245
5mA from LDO33 Pin
l 3.23 3.295 3.35
LDO33 Pin Load Regulation
LDO33 Pin Current Limit
ILDO33 = 0.1mA to 5mA
–0.25 –1
l 12 17.25 22
LDO33 Pin Undervoltage Lockout
LDO33 Falling
2.96 3.04 3.12
LDO33 Pin Undervoltage Lockout Hysteresis
35
Switching Regulator Control
Maximum Current Sense Threshold (VCSP – VCSN)
Maximum Current Sense Threshold (VCSN – VCSP)
Gain from VC to Maximum Current Sense Voltage
(VCSP-VCSN) (A5 in the Block Diagram)
SHDN Input Voltage High
Boost Mode, Minimum M3 Switch Duty Cycle
Buck Mode, Minimum M2 Switch Duty Cycle
Boost Mode
Buck Mode
SHDN Rising to Enable the Device
l 102 117 132
l 69 86 102
150
–150
l 1.184 1.234 1.284
SHDN Input Voltage High Hysteresis
50
SHDN Input Voltage Low
Device Disabled, Low Quiescent Current
l
0.35
UNITS
V
V
mA
µA
V
V
mA
mA
V
V
%
V
mV
mV
V
%
mA
V
mV
mV
mV
mV/V
mV/V
V
mV
V
For more information www.linear.com/8705
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LT8705
E LECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VIN = 12V, SHDN = 3V unless otherwise noted. (Note 3)
PARAMETER
CONDITIONS
MIN TYP MAX
SHDN Pin Bias Current
SWEN Rising Threshold Voltage (Note 5)
VSHDN = 3V
VSHDN = 12V
01
11 22
l 1.156 1.206 1.256
SWEN Threshold Voltage Hysteresis (Note 5)
22
MODE Pin Forced Continuous Mode Threshold
l 0.4
MODE Pin Burst Mode Range
l 1.0
1.7
MODE Pin Discontinuous Mode Threshold
l 2.3
Soft-Start Charging Current
VSS = 0.5V
Soft-Start Discharge Current
VSS = 0.5V
Voltage Regulator Loops (Refer to Block Diagram to Locate Amplifiers)
13 19 25
9.5
Regulation Voltage for FBOUT
Regulation Voltage for FBIN
Line Regulation for FBOUT and FBIN Error Amp Reference
Voltage
VC = 1.2V
VC = 1.2V
VIN = 12V to 80V
l 1.193 1.207 1.217
l 1.187 1.205 1.220
0.002 0.005
FBOUT Pin Bias Current
Current Out of Pin
15
FBOUT Error Amp EA4 gm
FBOUT Error Amp EA4 Voltage Gain
315
220
FBIN Pin Bias Current
Current Out of Pin
10
FBIN Error Amp EA3 gm
FBIN Error Amp EA3 Voltage Gain
http://www.DataSheet4U.com/
130
90
SRVO_FBIN Activation Threshold (Note 5)
SRVO_FBIN Activation Threshold Hysteresis (Note 5)
SRVO_FBOUT Activation Threshold (Note 5)
SRVO_FBOUT Activation Threshold Hysteresis (Note 5)
SRVO_FBIN, SRVO_FBOUT Low Voltage (Note 5)
(VVFFBBOIUNTF=alVlinIMgO)N_I(NR=egVuIlMatOioNn_OVUoTlt=ag0eVfor FBIN),
VFBOUT = VIMON_IN = VIMON_OUT = 0V
(VFBOUT Rising) – (Regulation Voltage for FBOUT),
VFBIN = 3V, VIMON_IN = VIMON_OUT = 0V
VFBIN = 3V, VIMON_IN = 0V, VIMON_OUT = 0V
I = 100μA
56 72 89
33
–37 –29 –21
15
l 110 330
SRVO_FBIN, SRVO_FBOUT Leakage Current (Note 5)
VSRVO_FBIN = VSRVO_FBOUT = 2.5V
Current Regulation Loops (Refer to Block Diagram to Locate Amplifiers)
l 01
Regulation Voltages for IMON_IN and IMON_OUT
Line Regulation for IMON_IN and IMON_OUT Error Amp
Reference Voltage
VC = 1.2V
VIN = 12V to 80V
l 1.191 1.208 1.223
0.002 0.005
CSPIN, CSNIN Bias Current
CSPIN, CSNIN Common Mode Operating Voltage Range
BOOST Capacitor Charge Control Block Not Active
ICSPIN + ICSNIN, VCSPIN = VCSNIN = 12V
31
l 1.5
80
CSPIN, CSNIN Differential Operating Voltage Range
l –100
100
VCSPIN-CSNIN to IMON_IN Amplifier A7 gm
VCSPIN – VCSNIN = 50mV, VCSPIN = 5.025V
0.95 1 1.05
l 0.94 1 1.06
IMON_IN Maximum Output Current
l 100
IMON_IN Overvoltage Threshold
l 1.55 1.61 1.67
IMON_IN Error Amp EA2 gm
IMON_IN Error Amp EA2 Voltage Gain
185
130
UNITS
µA
µA
V
mV
V
V
V
µA
µA
V
V
%/V
nA
µmho
V/V
nA
µmho
V/V
mV
mV
mV
mV
mV
µA
V
%/V
µA
V
mV
mmho
mmho
µA
V
µmho
V/V
8705p
4 For more information www.linear.com/8705



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