LTC3850/LTC3850-1
Dual, 2-Phase Synchronous Step-Down
Switching Controller
FEATURES
n Dual, 180° Phased Controllers Reduce Required
Input Capacitance and Power Supply Induced Noise
n High Efficiency: Up to 95%
n RSENSE or DCR Current Sensing
n ±1% 0.8V Output Voltage Accuracy
n Phase-Lockable Fixed Frequency 250kHz to 780kHz
n Supports Pre-Biased Output
n Dual N-Channel MOSFET Synchronous Drive
n Wide VIN Range: 4V to 24V (30V for LTC3850I)
Operation
n Adjustable Soft-Start Current Ramping or Tracking
n Foldback Output Current Limiting
n Power Good Output Voltage Monitor
n 28-Pin 4mm × 4mm, 4mm × 5mm QFN and Narrow
SSOP Packages
n AEC-Q100 Qualified for Automotive Applications
APPLICATIONS
n Notebook and Palmtop Computers
n Portable Instruments
n Battery-Operated Digital Devices
n DC Power Distribution Systems
All registered trademarks and trademarks are the property of their respective owners. Protected
by U.S. patents, including 5481178, 5705919, 5929620, 6100678, 6144194, 6177787,
6304066, 6580258.
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 (28V maximum/30V for LTC3850I) input supply
range encompasses most battery chemistries and inter-
mediate bus voltages.
Independent TK/SS pins for each controller ramp the
output voltages during start-up. Current foldback limits
MOSFET heat dissipation during short-circuit conditions.
The MODE/PLLIN pin selects among Burst Mode® opera-
tion, pulse-skipping mode, or continuous inductor cur-
rent mode and allows the IC to be synchronized to an
external clock.
The LTC3850 is available in low profile 28-pin 4mm ×
4mm, 4mm × 5mm QFN and narrow SSOP packages.
TYPICAL APPLICATION
VOUT1
3.3V
5A
High Efficiency Dual 3.3V/2.5V Step-Down Converter
2.2µH
2.2k
63.4k
100µF
6V
0.1µF
VIN PGOOD INTVCC
TG1 TG2
500kHz
BOOST1
BOOST2
SW1
LTC3850
BG1
SW2
BG2
MODE/PLLIN
PGND
ILIM FREQ/PLLFLTR
0.1µF
SENSE1+
RUN1
SENSE1–
VFB1
SENSE2+
RUN2
SENSE2–
VFB2
ITH1 ITH2
220pF
TK/SS1 SGND TK/SS2
20k 15k
0.1µF
0.1µF
4.7µF
0.1µF
22µF
50V
2.2µH
2.2k
0.1µF
10nF
10k
220pF
43.2k
15k 20k
VIN
7V TO
24V
VOUT2
2.5V
5A
100µF
6V
38501 TA01
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Efficiency
100
95
VIN = 12V
VOUT = 3.3V
90
EFFICIENCY
85
80
75
70
65 POWER LOSS
60
55
50
10
100 1000
LOAD CURRENT (mA)
10000
1000
100
10
10000
38501 TA01b
Rev. D
1
