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Analog Devices Semiconductor Electronic Components Datasheet

LTC7818 Datasheet

Buck/Buck/Boost Synchronous Controller

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LTC7818
40V, Low IQ, 3MHz,
Triple Output Buck/Buck/Boost Synchronous Controller
FEATURES
n Dual Buck Plus Single Boost Synchronous Controllers
n Low Operating IQ:
n 14μA (14V to 3.3V, Channel 1 On)
n Outputs Remain in Regulation Through Cold Crank
Down to 1V Input Supply Voltage
n Wide Bias Input Voltage Range: 4.5V to 40V
n Buck and Boost Output Voltages Up to 40V
n Spread Spectrum Operation
n RSENSE or DCR Current Sensing
n Programmable Fixed Frequency (100kHz to 3MHz)
n PassThru™/100% Duty Cycle Capable for
Synchronous Boost MOSFET
n Phase-Lockable Frequency (100kHz to 3MHz)
n Selectable Continuous, Pulse-Skipping, or Low
Ripple Burst Mode Operation at Light Loads
n Boost Channel Current Monitor Output
n Low Shutdown IQ: 1.5μA
n Small 40-Lead 6mm × 6mm QFN Package
APPLICATIONS
n Automotive and Transportation
n Industrial
n Military/Avionics
DESCRIPTION
The LTC®7818 is a high performance triple output (buck/
buck/boost) synchronous DC/DC switching regulator con-
troller that drives all N-channel power MOSFET stages.
Its constant-frequency current mode architecture allows
a phase-lockable switching frequency of up to 3MHz.
The LTC7818 operates from a wide 4.5V to 40V input
supply range. When biased from the output of the boost
converter or another auxiliary supply, the LTC7818 can
operate from an input supply as low as 1V after start-up.
The LTC7818 synchronous boost PassThru capability
minimizes losses in automotive start-stop applications.
The very low no-load quiescent current extends operating
run time in battery powered systems. OPTI-LOOP® com-
pensation allows the transient response to be optimized
over a wide range of output capacitance and ESR values.
The LTC7818 features a precision 0.8V reference for the
bucks, 1.2V reference for the boost and a power good
output indicator.
The LTC7818 additionally features spread spectrum oper-
ation which significantly reduces the peak radiated and
conducted noise on both the input and output supplies,
making it easier to comply with electromagnetic interfer-
ence (EMI) standards.
All registered trademarks and trademarks are the property of their respective owners. Protected
by U.S. Patents including 5481178, 5705919, 5929620, 6144194, 6177787, 6580258.
TYPICAL APPLICATION
VOUT3
REGULATED TO 10V
WHEN VIN < 10V
FOLLOWS VIN
WHEN VIN >10V
150µF
22µF
VIN
1V TO 38V
STARTUP
ABOVE 5V
1.5mΩ 1.4µH
150µF
0.1µF
VOUT3
0.1µF
4.7µF
BOOST1,2,3
VFB3
TG3
BOOST3
VBIAS
TG1
BOOST1
SW3
SW1
BG3
BG1
LTC7818
SENSE3
SENSE3+
RUN1,2,3
ITH1,2,3
TRACK/SS1,2,3
INTVCC
VPRG3
SENSE1+
SENSE1–
VFB1
TG2
BOOST2
SW2
BG2
MODE
PLLIN/SPREAD
FREQ
GND
SENSE2+
SENSE2
VFB2
EXTVCC
7818 TA01a
0.1µF
0.9µH
2mΩ
VOUT3
0.1µF
1.8µH 3mΩ
VOUT2
22µF
VOUT1
3.3V
12A
330µF
210k
68.1k
10µF
VOUT2
5V
10A
330µF
357k
68.1k
Document Feedback
For more information www.analog.com
ALTuCLtCo7Trm8aC1n7o8k8ti1AvR8euetsRWopemaosvnopestoifevonerstomeWataoCvaoelfCdoorCmldrank
VOLTAGE
2V/DIV
VBATT
VOUT3
VOUT2
VOUT1
0V
TIME (10ms/DIV)
7818 TA01b
Rev. A
1


Analog Devices Semiconductor Electronic Components Datasheet

LTC7818 Datasheet

Buck/Buck/Boost Synchronous Controller

No Preview Available !

LTC7818
TABLE OF CONTENTS
Features...................................................... 1
Applications................................................. 1
Typical Application......................................... 1
Description.................................................. 1
Absolute Maximum Ratings............................... 3
Order Information........................................... 3
Pin Configuration........................................... 3
Electrical Characteristics.................................. 4
Typical Performance Characteristics.................... 7
Pin Functions............................................... 11
Functional Diagram....................................... 13
Operation................................................... 14
Main Control Loop................................................... 14
Power and Bias Supplies (VBIAS, EXTVCC,
and INTVCC)............................................................. 14
Shutdown and Start-Up (RUN1, RUN2, RUN3
and TRACK/SS1, TRACK/SS2, SS3 Pins)................ 14
Light Load Operation: Burst Mode Operation, Pulse-
Skipping, or Forced Continuous Mode (MODE Pin).......15
Frequency Selection, Spread Spectrum, and Phase-
Locked Loop (FREQ and PLLIN/SPREAD Pins)........ 16
Boost Controller Operation When VIN > VOUT.......... 16
Boost Controller at Low Input Voltage..................... 17
Buck Controller Output Overvoltage Protection....... 17
Buck Foldback Current............................................. 17
Channel 1 Power Good (PGOOD1)........................... 17
Boost Overvoltage Indicator (OV3).......................... 17
Applications Information................................. 18
Inductor Value Calculation....................................... 18
Inductor Core Selection........................................... 18
Current Sense Selection.......................................... 18
Low Value Resistor Current Sensing........................ 19
Inductor DCR Current Sensing.................................20
Setting the Operating Frequency............................. 21
Selecting the Light Load Operating Mode................22
Power MOSFET Selection........................................23
Boost CIN and COUT Selection.................................. 24
Buck CIN and COUT Selection................................... 24
Setting the Buck Output Voltage..............................25
Setting Boost Output Voltage (VPRG3 Pin).............26
RUN Pins and Undervoltage Lockout.......................26
Soft-Start and Tracking (TRACK/SS1, TRACK/
SS2, SS3 Pins)........................................................26
Single Output Two-Phase Operation........................ 27
INTVCC Regulators................................................... 28
Topside MOSFET Driver Supply (CB, DB).................29
Minimum On-Time Considerations..........................29
Boost Channel Current Monitor (IMON3).................29
Fault Conditions: Buck Current Limit and Foldback....... 30
Fault Conditions: Buck Overvoltage Protection
(Crowbar)................................................................. 30
Fault Conditions: Overtemperature Protection.........30
Phase-Locked Loop and Frequency Synchronization... 30
Efficiency Considerations........................................ 31
Checking Transient Response.................................. 32
Buck Design Example.............................................. 32
PC Board Layout Checklist......................................34
PC Board Layout Debugging....................................35
Typical Applications....................................... 37
Package Description...................................... 42
Revision History........................................... 43
Typical Application........................................ 44
Related Parts............................................... 44
Rev. A
2
For more information www.analog.com



Part Number LTC7818
Description Buck/Buck/Boost Synchronous Controller
Maker Analog Devices
Total Page 3 Pages
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LTC7818 Datasheet PDF





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