Document
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 phaselockable 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 (%)
POWER LOSS (mW)
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
LTC3869/LTC3869-2
Absolute Maximum Ratings (Note 1)
Input Supply Voltage: VIN............................ 40V to –0.3V Top Side Driver Voltages:
BOOST1, BOOST2....................................... 46V to –0.3V
Switch Voltage: SW1, SW2............................ 40V to –5V
INTVCC, RUN1, RUN2, PGOOD, EXTVCC, BOOST1-SW1, BOOST2-SW2........................ 6V to –0.3V SENSE1+, SENSE2+, SENSE1–, SENSE2– Voltages.......................................13V to –0.3V
MODE/PLLIN, ILIM, TK/SS1, TK/SS2, FREQ Voltages....................................... INTVCC to –0.3V
ITH1, ITH2, VFB1, VFB2 Voltages.............. INTVCC to –0.3V INTVCC Peak Output Current.................................100mA Operating Junction Temperature Range
(Note 2)................................................... –40°C to 125°C
Junction Temperature (Note 3).............................. 125°C
Storage Temperature Range................... –65°C to 150°C
Lead Temperature (Soldering, 10 sec)
GN Package....................................................... 300°C
Pin Configuration
TOP VIEW
SENSE1+ RUN1 FREQ MODE/PLLIN SW1 TG1
28 27 26 25 24 23
SENSE1– 1
22 BOOST1
TK/SS1 2
21 BG1
ITH1 3 VFB1 4 VFB2 5 ITH2 6 TK/SS2 7 SENSE2– 8
SGND 29
20 VIN 19 INTVCC 18 BG2 17 PGND 16 BOOST2 15 TG2
9 10 11 12 13 14
SENSE2+ RUN2 ILIM
EXTVCC PGOOD
SW2
UFD PACKAGE 28-LEAD (4mm × 5mm) PLASTIC QFN
TJMAX = 125°C, θJA = 34°C/W, EXPOSED PAD (PIN 29) IS SGND, MUST BE
SOLDERED TO PCB
TOP VIEW
RUN1 1 SENSE1+ 2 SENSE1– 3
VFB1 4 TK/SS1 5
ITH1 6 SGND 7
ITH2 8 TK/SS2 9
VFB2 10 SENSE2– 11 SENSE2+ 12
RUN2 13 EXTVCC 14
28 FREQ 27 MODE/PLLIN 26 SW1 25 TG1 24 BOOST1 23 BG1 22 VIN 21 INTVCC 20 BG2 19 PGND 18 BOOST2 17 TG2 16 SW2 15 PGOOD
GN PACKAGE 28-LEAD PLASTIC SSOP
TJMAX = 125°C, θJA = 80°C/W
TOP VIEW
SENSE1– SENSE1+ RUN1 FREQ MODE/PLL.