Features
n Dual, 180° Phased Controllers Reduce Required
Input Capacitance and Power Supply Induced Noise
n Accurate Multiphase Current Matching
n RSENSE or DCR Current Sensing
n ±0.75% 0.6V Output Voltage Accuracy
n Phase-Lockable Fixed Frequency 250kHz to 780kHz
n High Efficiency: Up to 95%
n Dual N-channel MOSFET Synchronous Drive
n Wide VIN Range: 4V to 38V (40V Max) Operation
n Wide VOUT Range: 0.6V to 12.5V Operation
n Adjustable Soft-Start Current Ramping or Tracking
n Foldback Output Current Limiting
n Output Overvoltage Protection
n Power Good Output Voltage Monitor
n 5V Low Dropout Regulator
n Small 28-Lead QFN and Narrow SSOP Packages
Applications
n Server Systems
n Telecom Systems
n Industrial and Medical Instruments
n High Power Battery-Operated Devices
n DC Power Distribution Systems
LTC3869/LTC3869-2
Dual, 2-Phase
Synchronous Step-Down
DC/DC Controllers
Description
The LTC®3869 is a high performance dual synchronous
step-down switching regulator controller that drives all
N-channel synchronous power MOSFET stages. A constant
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. 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 limits MOSFET heat dissipation
during short-circuit conditions. 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.
The LTC3869 is available in low profile 4mm × 4mm and
4mm × 5mm QFN packages. The LTC3869-2 is available
in an SSOP-28 package. The LTC3869 is pin-compatible
with the LTC3850.
L, LT, LTC, LTM, Linear Technology, the Linear logo, µModule, OPTI-LOOP, Burst Mode
and PolyPhase are registered trademarks and No RSENSE is a trademark of Linear Technology
Corporation. All 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 5V/3.3V Step-Down Converter
VIN
7V TO
+
4.7µF
24V
22µF
VIN
INTVCC
TG1
TG2
BOOST1
SW1
BG1
LTC3869
BOOST2
SW2
BG2
PGND
VOUT1
5V
5A
147k
+
47µF
SENSE1+
SENSE2+
SENSE1–
SENSE2–
VFB1
VFB2
ITH1
FREQ
470pF
20k
ITH2
TK/SS1 SGND TK/SS2
15k
0.1µF
0.1µF
470pF
122k
15k
90.9k +
VOUT2
3.3V
5A
56µF
20k
PINS NOT USED IN
THIS CIRCUIT:
ILIM, MODE/PLLIN,
PGOOD, RUN1, RUN2
3869 TA01
For more information www.linear.com/LTC3869
Efficiency and Power Loss
100
90
80
70
60
50
40
30
20
10
0
0.01
VIN = 12V, VOUT = 3.3V
VIN = 12V, VOUT = 5V
1300
1200
1100
EFFICIENCY
1000
900
800
700
600
POWER LOSS 500
0.1
1
LOAD CURRENT (A)
400
10
3869 TA01b
38692fb
1
