LTC3869/LTC3869-2
Dual, 2-Phase
Synchronous Step-Down
DC/DC Controllers
FEATURES
DESCRIPTION
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Dual, 180° Phased Controllers Reduce Required
The LTC®3869 is a high performance dual synchronous
step-down switching regulator controller that drives all
N-channelsynchronouspowerMOSFETstages.Aconstant
frequency current mode architecture allows a phase-
lockable frequency of up to 780kHz. Power loss and noise
due to the ESR of the input capacitors are minimized by
operating the two controller output stages out-of-phase.
OPTI-LOOP® compensation allows the transient response
to be optimized over a wide range of output capacitance
and ESR values. The LTC3869 features a precision 0.6V
reference and a power good output indicator. A wide 4V
to 38V input supply range encompasses most battery
chemistries. Independent TK/SS pins for each controller
ramp the output voltage during start-up. Current foldback
limitsMOSFETheatdissipationduringshort-circuitcondi-
tions. The MODE/PLLIN pin selects among Burst Mode®
operation, pulse-skipping mode, or continuous inductor
current mode and allows the IC to be synchronized to an
external clock.
Input Capacitance and Power Supply Induced Noise
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Accurate Multiphase Current Matching
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R
SENSE
or DCR Current Sensing
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0ꢀ.75 0ꢀꢁ6 ꢂutput 6oltage Accuracy
Phase-Lockable Fixed Frequency 270kHz to .80kHz
High Efficiency: Up to 95%
Dual N-channel MOSFET Synchronous Drive
Wide V Range: 4V to 38V (40V Max) Operation
IN
Wide V
Range: 0.6V to 12.5V Operation
OUT
Adjustable Soft-Start Current Ramping or Tracking
Foldback Output Current Limiting
Output Overvoltage Protection
Power Good Output Voltage Monitor
5V Low Dropout Regulator
Small 28-Lead QFN and Narrow SSOP Packages
APPLICATIONS
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Server Systems
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Telecom Systems
TheLTC3869ispincompatiblewithLTC3850andis available
inbothlowprofile28-leadQFNandnarrowSSOPpackages.
L, LT, LTC, LTM, Linear Technology, the Linear logo, OPTI-LOOP, Burst Mode and PolyPhase
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Industrial and Medical Instruments
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High Power Battery-Operated Devices
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DC Power Distribution Systems
are registered trademarks and No R
is a trademark of Linear Technology Corporation. All
SENSE
other trademarks are the property of their respective owners. Protected by U.S. Patents including
5481178, 5705919, 5929620, 6100678, 6144194, 6177787, 6580258, 6498466, 6611131.
TYPICAL APPLICATION
High Efficiency Dual 76/3ꢀ36 Step-Down Converter
Efficiency and Power Loss
100
90
80
70
60
50
40
30
20
10
0
1300
1200
1100
1000
900
V
IN
V
V
= 12V, V
= 12V, V
= 3.3V
= 5V
IN
IN
OUT
OUT
7V TO
24V
+
22µF
1µF
4.7µF
V
PGOOD INTV
IN
CC
TG2
TG1
EFFICIENCY
0.1µF
0.1µF
BOOST1
SW1
BOOST2
SW2
3.2µH
2.2µH
800
LTC3869
BG1
BG2
700
f
IN
MODE/PLLIN
PGND
FREQ
500kHz
600
I
LIM
+
+
POWER LOSS
SENSE1
SENSE2
RUN2
SENSE2
500
RUN1
–
–
V
V
OUT1
5V
5A
SENSE1
400
OUT2
0.01
0.1
1
10
3.3V
V
V
FB1
TH1
FB2
TH2
5A
LOAD CURRENT (A)
147k
90.9k
I
I
3869 TA01b
470pF
15k
470pF
15k
TK/SS1 SGND TK/SS2
+
+
20k
20k
56µF
122k
47µF
0.1µF
0.1µF
3869 TA01
3869f
1