LTC3899
60V Low I , Triple
Q
Output, Buck/Buck/Boost
Synchronous Controller
DESCRIPTION
FEATURES
DualBuckPlusSingleBoost SynchronousControllers The LTC®3899 is a high performance triple output (buck/
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Wide Bias Input Voltage Range: 4.5V to 60V
Outputs Remain in Regulation Through Cold Crank
Down to a 2.2V Input Supply Voltage
buck/boost) DC/DC switching regulator controller that
drives all N-channel synchronous power MOSFET stages.
The constant frequency current mode architecture allows
aphase-lockablefrequencyofupto850kHz. TheLTC3899
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Buck and Boost Output Voltages Up to 60V
Adjustable Gate Drive Level 5V to 10V (OPTI-DRIVE) operates from a wide 4.5V to 60V input supply range.
No External Bootstrap Diodes Required
Low Operating I : 29μA (One Channel On)
When biased from the output of the boost converter or
another auxiliary supply, the LTC3899 can operate from
an input supply as low as 2.2V after start-up.
Q
100% Duty Cycle for Boost Synchronous MOSFET
Phase-Lockable Frequency (75kHz to 850kHz)
Programmable Fixed Frequency (50kHz to 900kHz)
Very Low Dropout Operation: 99% Duty Cycle (Bucks)
The gate drive for the LTC3899 can be programmed from
5V to 10V to allow the use of logic-level or standard-level
FETs and to maximize efficiency. Internal switches in the
top gate drivers eliminate the need for external bootstrap
diodes. The 29μA no-load quiescent current extends op-
eratingruntimeinbattery-poweredsystems.OPTI-LOOP®
compensationallowsthetransientresponsetobeoptimized
over a wide range of output capacitance and ESR values.
Low Shutdown I : 3.6μA
Q
Fixed or Adjustable Boost Output Voltage Saves I
Q
Small 38-Lead 5mm × 7mm QFN and TSSOP Packages
APPLICATIONS
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Automotive Always-On and Start-Stop Systems
L, LT, LTC, LTM, Burst Mode, OPTI-LOOP, Linear Technology and the Linear logo are
registered trademarks of Linear Technology Corporation. All other trademarks are the property
of their respective owners. Protected by U.S. Patents including 5481178, 5705919, 5929620,
6144194, 6177787, 6580258.
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Distributed DC Power Systems
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Multioutput Buck-Boost Applications
TYPICAL APPLICATION
High Efficiency Wide Input Range Dual 5V/8.5V Converter
Efficiency vs Output Current
V
OUT3
95
REGULATED AT 10V
V
V
= 12V
= 5V
IN
OUT
33µF
WHEN V < 10V
IN
RUN1, 2, 3
V
BIAS
TG1
FOLLOWS V WHEN
IN
94
93
92
91
90
89
88
Burst Mode OPERATION
V
FB3
V
IN
> 10V
0.1µF
TG3
BOOST1
SW1
4.9µH
V
5V
5A
9mΩ
OUT1
0.1µF
BOOST3
SW3
1.2µH
3mΩ
V
BG1
IN
2.2V TO 60V
(START-UP
ABOVE 5V)
LTC3899
33µF
BG3
+
–
SENSE1
SENSE1
357k
–
+
SENSE3
SENSE3
GATE DRIVE (DRV
)
V
CC
FB1
5V
6V
8V
68.1k
220µF
DRV
CC
INTV
CC
4.7µF
0.1µF
10V
TG2
0.1µF
0.01
0.1
1
10
BOOST2
SW2
ITH1,2,3
6.5µH
V
8.5V
3A
15mΩ
OUT2
OUTPUT CURRENT(A)
3899 TA01b
BG2
DRVSET
VPRG3
+
–
SENSE2
SENSE2
649k
V
FB2
GND
68.1k
68µF
3899 TA01a
3899fa
1
For more information www.linear.com/LTC3899