LTC3850-2 Datasheet, PDF (1/36 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 30V 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 Narrow SSOP Package}
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.
LTC3850-2
Dual, 2-Phase
Synchronous Step-Down
Switching Controller
DESCRIPTION
The LTC^®3850-2 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
frequency 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 LTC3850-2 features a precision 0.8V
reference and a power good output indicator. A wide 4V
to 30V 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 LTC3850-2 is identical to the LTC3850-1, except they
have different pin assignments.
TYPICAL APPLICATION
V_OUT1
3.3V
5A
2.2μH
2.2k
63.4k
100μF
6V
High Efficiency Dual 3.3V/2.5V Step-Down Converter
0.1μF
V_IN PGOOD INTV_CC
TG1
TG2
BOOST1
BOOST2
SW1
SW2
LTC3850-2
BG1
BG2
500kHz MODE/PLLIN
PGND
EXT_VCC 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
26V
V_OUT2
2.5V
5A
100μF
6V
38502 TA01
Efficiency
100
V_IN = 12V
95 V_OUT = 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
38502 TA01b
38502f
1