LTC3851-1_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 _{Power Good Output Voltage Monitor}
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 _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}
or 3mm × 3mm QFN Package
APPLICATIONS
n _{Automotive Systems}
n _{Telecom Systems}
n _{Industrial Equipment}
n _{Distributed DC Power Systems}
LTC3851-1
Synchronous
Step-Down Switching
Regulator Controller
DESCRIPTION
The LTC^®3851-1 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 LTC3851-1 features a precision 0.8V
reference and a power good indicator. A wide 4V to 38V (40V
absolute maximum) input supply range encompasses most
battery configurations and intermediate bus voltages.
The TK/SS pin ramps the output voltage during start-up
and shutdown with coincident or ratiometric tracking.
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 identical to the LTC3851 except that the
I_LIM pin is replaced by PGOOD.
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
INTV_CC
82.5k
100k
PGO0D
V_IN
0.1μF
0.1μF
FREQ/PLLFLTR TG
RUN
SW
LTC3851-1
TK/SS BOOST
0.1μF
0.68μH
3.01k
22μF
V_IN
4.5V TO 38V
V_OUT
3.3V
15A
330μF
s2
2200pF
15k
INTV_CC
I_TH
330pF
BG
GND
SENSE⁺
MODE/PLLIN
SENSE^–
V_FB
4.7μF
0.047μF 30.1k
154k
48.7k
38511 TA01a
Efficiency and Power Loss
vs Load Current
100
V_IN = 12V
95 V_OUT = 3.3V
90
EFFICIENCY
10000
85
1000
80
POWER LOSS
75
70
65
100
60
55
50
10
10
100
1000 10000 100000
LOAD CURRENT (mA)
38511TA01b
38511fa
1