LTC3851A_15 Datasheet, PDF (1/30 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}
LTC3851A
Synchronous
Step-Down Switching
Regulator Controller
Description
The LTC^®3851A 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 LTC3851A 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 al-
lows the IC to be synchronized to an external clock. The
LTC3851A contains an improved PLL compared to the
LTC3851.
The LTC3851A-1 is a version with a power good output
signal instead of adjustable current limit.
L, LT, LTC, LTM, Burst Mode, OPTI-LOOP, Linear Technology and the Linear logo are registered
trademarks and No R_SENSE, UltraFast are 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
LTC3851A
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
×2
0.047µF 30.1k
154k
48.7k
3851A 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)
3851A TA01b
3851afa
1