LTC3850_15 Datasheet, PDF (1/38 Pages) Linear Technology – 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 _{Output Overvoltage Protection}
n _{Power Good Output Voltage Monitor}
n _{28-Pin 4mm × 4mm, 4mm × 5mm QFN and Narrow}
SSOP Packages
APPLICATIONS
n _{Notebook and Palmtop Computers}
n _{Portable Instruments}
n _{Battery-Operated Digital Devices}
n _{DC Power Distribution Systems}
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.
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 (28V maximum/30V for LTC3850I) input supply range
encompasses most battery chemistries and intermediate
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 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.
The LTC3850 is available in low profile 28-pin 4mm × 4mm,
4mm × 5mm QFN and narrow SSOP packages.
TYPICAL APPLICATION
V_OUT1
3.3V
5A
High Efficiency Dual 3.3V/2.5V Step-Down Converter
2.2µH
2.2k
63.4k
100µF
6V
0.1µF
V_IN PGOOD INTV_CC
TG1
TG2
BOOST1
BOOST2
SW1
SW2
LTC3850
BG1
BG2
500kHz MODE/PLLIN
PGND
I_LIM
FREQ/PLLFLTR
0.1µF
SENSE1⁺
RUN1
SENSE1^–
V_FB1
SENSE2⁺
RUN2
SENSE2^–
V_FB2
I_TH1
I_TH2
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
V_IN
7V TO
24V
V_OUT2
2.5V
5A
100µF
6V
38501 TA01
Efficiency
100
V_IN = 12V
95 V_OUT = 3.3V
90
85
80
75
EFFICIENCY
70
65
60
55
50
10
POWER LOSS
100
1000
LOAD CURRENT (mA)
10000
1000
100
10
10000
38501 TA01b
38501fc
1