LTC3823
TM
Fast No R
Step-Down
SENSE
Synchronous DC/DC Controller
with Differential Output Sensing,
Tracking and PLL
FEATURES
DESCRIPTION
TheLTC®3823isasynchronousstep-downswitchingregu-
latorcontrollerwithtrueremotedifferentialoutputsensing
andoutputvoltageup/downtrackingcapability.Itsadvanced
functionsandhighaccuracyreferenceareidealforpowering
high performance server, ASIC and computer memory
systems.
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Wide V Range: 4.5V to 36V
IN
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0.67%, 0.6V Reference Voltage
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Output Voltage Tracking Capability
True Remote Sensing Differential Amplifier
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Sense Resistor Optional
True Current Mode Control
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2% to 90% Duty Cycle at 200kHz
The LTC3823 uses a constant on-time, valley current
mode control architecture to deliver very low duty fac-
tors without requiring a sense resistor. The operating
frequency is selected by an external resistor and is com-
pensatedforvariationsininputsupplyvoltage. Aninternal
phase-locked loop allows the IC to be synchronized to an
external clock.
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t
< 100ns
ON(MIN)
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Phase-Locked Loop Frequency Synchronization
Powerful Dual N-Channel MOSFET Driver
Adjustable Cycle-by-Cycle Current Limit
Adjustable Switching Frequency
Programmable Soft-Start
Current Foldback Protection (Disabled at Start-Up)
Output Overvoltage Protection
Micropower Shutdown: 30μA
Power Good Output Voltage Monitor Tracks the
Reference Input Pin
Available in (5mm × 5mm) 32-Lead QFN and
28-Lead SSOP Narrow Packages
Fault protection is provided by an overvoltage compara-
tor and input undervoltage lockout. The regulator current
limit is user programmable. A wide supply range allows
voltages as high as 36V to be stepped down to as low as
a 0.6V output. When using remote sense, output voltages
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up to 3.3V can be developed, and up to 90% of V without
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remote sense. Power supply sequencing is accomplished
APPLICATIONS
using an external soft-start timing capacitor.
L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and
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Distributed Power Systems
Server Power Supplies
No R
is a trademark of Linear Technology Corporation. All other trademarks are the
SENSE
property of their respective owners. Protected by U.S. Patents including 5481178, 5847554,
6580258, 6304066, 6476589, 6774611.
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TYPICAL APPLICATION
Efficiency and Power Loss
vs Load Current
High Efficiency Step-Down Converter
97
96
95
94
93
92
91
90
89
88
87
10
1
PGOOD
I
ON
V
V
= 5V
IN
OUT
68k
V
= 2.5V
IN
5V TO 28V
V
0.01μF
IN
FIGURE 12 CIRCUIT
10k
10μF
35V
s3
Si4884
1.8μH
TG
PLLFLTR
PLLIN
V
OUT
EFFICIENCY
0.1μF
SW
2.5V
10A
TRACK/SS
0.22μF
BOOST
+
180μF
4V
s2
I
TH
POWER LOSS
10k
LTC3823
CMDSH-3
1000pF
V
0.1
0.01
SGND
RUN
INTV
DRV
CC
CC
Si4874
B340A
V
ON
BG
OUT
+
SENSE
V
RNG
10μF
V
–
DIFFOUT
SENSE
9.5k
0.1
1
10
3823 TA01b
PGND
LOAD CURRENT (A)
V
FB
+
V
V
OUTSENSE
3k
–
OUTSENSE
3823 TA01a
3823fd
1