LTC3850/LTC3850-1
Dual, 2-Phase
Synchronous Step-Down
Switching Controller
DESCRIPTION
The LTC®3850 is a high performance dual synchronous
step-down switching regulator controller that drives all
N-channel power MOSFET stages. A constant-frequency
current mode architecture allows a phase-lockable fre-
quency of up to 780kHz. Power loss and supply noise 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 LTC3850 features a precision 0.8V
reference and a power good output indicator. A wide 4V to
24V(28Vmaximum/30VforLTC3850I)inputsupplyrange
encompasses most battery chemistries and intermediate
bus voltages.
FEATURES
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Dual, 180° Phased Controllers Reduce Required
Input Capacitance and Power Supply Induced Noise
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High Efficiency: Up to 95%
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R
or DCR Current Sensing
SENSE
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1% 0.8V ꢀutput Voltage Accuracy
Phase-Lockable Fixed Frequency 250kHz to 780kHz
Supports Pre-Biased Output
Dual N-Channel MOSFET Synchronous Drive
Wide V Range: 4V to 24V (30V for LTC3850I)
IN
Operation
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Adjustable Soft-Start Current Ramping or Tracking
Foldback Output Current Limiting
Output Overvoltage Protection
Power Good Output Voltage Monitor
28-Pin 4mm × 4mm, 4mm × 5mm QFN and Narrow
SSOP Packages
Independent TK/SS pins for each controller ramp the
output voltages during start-up. Current foldback limits
MOSFET heat dissipation during short-circuit condi-
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.
APPLICATIONS
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Notebook and Palmtop Computers
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Portable Instruments
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Battery-Operated Digital Devices
DC Power Distribution Systems
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TheLTC3850isavailableinlowprofile28-pin4mm×4mm,
4mm × 5mm QFN and narrow SSOP packages.
L, LT, LTC, LTM, OPTI-LOOP and BURST MODE 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, 6100678, 6144194, 6177787, 6304066, 6580258.
TYPICAL APPLICATION
High Efficiency Dual 3.3V/2.5V Step-Down Converter
Efficiency
V
IN
100
95
10000
1000
100
7V TO
24V
22μF
50V
V
V
= 12V
IN
OUT
4.7μF
= 3.3V
EFFICIENCY
V
PGOOD INTV
IN
CC
90
TG1
TG2
0.1μF
0.1μF
85
BOOST1
SW1
BOOST2
SW2
2.2μH
2.2μH
80
75
LTC3850
2.2k
BG2
PGND
BG1
70
65
60
55
50
2.2k
500kHz
MODE/PLLIN
I
FREQ/PLLFLTR
POWER LOSS
1000
LIM
+
–
+
SENSE1
RUN1
SENSE1
SENSE2
0.1μF
0.1μF
RUN2
–
V
SENSE2
OUT1
3.3V
5A
V
OUT2
10
10000
V
FB1
V
FB2
2.5V
10
100
5A
63.4k
43.2k
I
I
LOAD CURRENT (mA)
TH1
TH2
10nF
10k
220pF
15k
220pF
15k
38501 TA01b
TK/SS1 SGND TK/SS2
100μF
6V
100μF
6V
20k
20k
0.1μF
0.1μF
38501 TA01
38501fb
1