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LTC3851-1

Description
Synchronous Step-Down Switching Regulator Controller
File Size342KB,28 Pages
ManufacturerLinear ( ADI )
Websitehttp://www.analog.com/cn/index.html
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LTC3851-1 Overview

Synchronous Step-Down Switching Regulator Controller

FEATURES
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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.
Wide V
IN
Range: 4V to 38V Operation
R
SENSE
or DCR Current Sensing
±1% Output Voltage Accuracy
Power Good Output Voltage Monitor
Phase-Lockable Fixed Frequency: 250kHz to 750kHz
Dual N-Channel MOSFET Synchronous Drive
Very Low Dropout Operation: 99% Duty Cycle
Adjustable Output Voltage Soft-Start or Tracking
Output Current Foldback Limiting
Output Overvoltage Protection
OPTI-LOOP
®
Compensation Minimizes C
OUT
Selectable Continuous, Pulse-Skipping or
Burst Mode
®
Operation at Light Loads
Low Shutdown I
Q
: 20μA
V
OUT
Range: 0.8V to 5.5V
Thermally Enhanced 16-Lead MSOP
or 3mm
×
3mm QFN Package
APPLICATIONS
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Automotive Systems
Telecom Systems
Industrial Equipment
Distributed DC Power Systems
TYPICAL APPLICATION
High Efficiency Synchronous Step-Down Converter
100k
INTV
CC
82.5k
0.1μF
PGO0D
V
IN
0.68μH
0.1μF
3.01k
INTV
CC
I
TH
15k
330pF
PLLIN/MODE
SENSE
V
FB
BG
GND
SENSE
+
0.047μF
30.1k
154k
4.7μF
FREQ/PLLFLTR TG
RUN
SW
LTC3851-1
BOOST
TK/SS
22μF
V
IN
4.5V TO 38V
V
OUT
3.3V
15A
330μF
2
Efficiency and Power Loss
vs Load Current
100
V
IN
= 12V
95 V
OUT
= 3.3V
EFFICIENCY
POWER LOSS (mW)
1000
POWER LOSS
10000
90
EFFICIENCY (%)
85
80
75
70
65
60
55
50
10
0.1μF
2200pF
100
48.7k
38511 TA01a
100
1000
10000
LOAD CURRENT (mA)
10
100000
38511TA01b
38511f
1

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