LTC3851
1
3851fb
TYPICAL APPLICATION
FEATURES
APPLICATIONS
DESCRIPTION
Synchronous
Step-Down Switching
Regulator Controller
The LTC
®
3851 is a high performance synchronous
step-down switching regulator controller that drives
an all N-channel synchronous power MOSFET stage. A
con stant 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.
High Effi ciency Synchronous Step-Down Converter
n
Wide V
IN
Range: 4V to 38V Operation
n
R
SENSE
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 C
OUT
n
Selectable Continuous, Pulse-Skipping or
Burst Mode
®
Operation at Light Loads
n
Low Shutdown I
Q
: 20µA
n
V
OUT
Range: 0.8V to 5.5V
n
Thermally Enhanced 16-Lead MSOP, 16-Lead Narrow
SSOP or 3mm × 3mm QFN Package
n
Automotive Systems
n
Telecom Systems
n
Industrial Equipment
n
Distributed DC Power Systems
Effi ciency and Power Loss
vs Load Current
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.
I
LIM
RUN
TK/SS
I
TH
FREQ/PLLFLTR
V
IN
TG
SW
INTV
CC
MODE/PLLIN
BG
SENSE
+
SENSE
–
V
FB
GND
0.1µF
0.047µF
3.01k
LTC3851
22µF
V
IN
4.5V TO 36V
V
OUT
3.3V
15A
3851 TA01a
0.68µH
30.1k
330pF
2200pF
0.1µF
330µF
s2
BOOST
15k
154k
48.7k
82.5k
0.1µF
4.7µF
LOAD CURRENT (mA)
10
70
EFFICIENCY (%)
POWER LOSS (mW)
75
80
85
90
100 1000 10000 100000
3851TA01b
65
60
55
50
95
100
1000
100
10
10000
V
IN
= 12V
V
OUT
= 3.3V
EFFICIENCY
POWER LOSS