LTC3851_15 Datasheet, PDF (1/28 Pages) Linear Technology – Synchronous Step-Down Switching Regulator Controller

FEATURES
n _{Wide VIN Range: 4V to 38V Operation}
n _{RSENSE or DCR Current Sensing}
n _{±1% Output Voltage Accuracy}
n _{Phase-Lockable Fixed Frequency: 250kHz to 750kHz}
n _{Dual N-Channel MOSFET Synchronous Drive}
n _{Very Low Dropout Operation: 99% Duty Cycle}
n _{Adjustable Output Voltage Soft-Start or Tracking}
n _{Output Current Foldback Limiting}
n _{Output Overvoltage Protection}
n _{5V Internal Regulator}
n _OPTI-LOOP^® _{Compensation Minimizes COUT}
n _{Selectable Continuous, Pulse-Skipping or}
Burst Mode^® Operation at Light Loads
n _{Low Shutdown IQ: 20μA}
n _{VOUT Range: 0.8V to 5.5V}
n _{Thermally Enhanced 16-Lead MSOP, 16-Lead Narrow}
SSOP or 3mm × 3mm QFN Package
APPLICATIONS
n _{Automotive Systems}
n _{Telecom Systems}
n _{Industrial Equipment}
n _{Distributed DC Power Systems}
LTC3851
Synchronous
Step-Down Switching
Regulator Controller
DESCRIPTION
The LTC^®3851 is a high performance synchronous
step-down switching regulator controller that drives
an all N-channel synchronous power MOSFET stage. A
constant frequency current mode architecture allows a
phase-lockable frequency of up to 750kHz.
OPTI-LOOP compensation allows the transient response
to be optimized over a wide range of output capacitance
and ESR values. The LTC3851 features a precision 0.8V
reference that is compatible with a wide 4V to 38V input
supply range.
The TK/SS pin ramps 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 at light loads and allows
the IC to be synchronized to an external clock.
The LTC3851-1 is a version with a power good output
signal instead of adjustable current limit.
L, LT, LTC, LTM, Burst Mode and OPTI-LOOP are registered trademarks of Linear Technology
Corporation. All other trademarks are the property of their respective owners. Protected by
U.S. Patents including 5408150, 5481178, 5705919, 5929620, 6304066, 6498466, 6580258,
6611131.
TYPICAL APPLICATION
High Efficiency Synchronous Step-Down Converter
82.5k
I_LIM
V_IN
0.1μF
0.1μF
FREQ/PLLFLTR TG
RUN
SW
LTC3851
TK/SS BOOST
2200pF
15k
INTV_CC
I_TH
330pF
BG
GND
SENSE⁺
MODE/PLLIN
SENSE^–
V_FB
0.1μF
4.7μF
0.68μH
3.01k
V_IN
22μF ^{4.5V TO 36V}
V_OUT
3.3V
15A
330μF
s2
0.047μF 30.1k
154k
48.7k
3851 TA01a
Efficiency and Power Loss
vs Load Current
100
V_IN = 12V
95 V_OUT = 3.3V
90
EFFICIENCY
85
80
10000
1000
75
POWER LOSS
70
65
100
60
55
50
10
10
100
1000 10000 100000
LOAD CURRENT (mA)
3851TA01b
3851fb
1