LTC3856
2-Phase Synchronous
Step-Down DC/DC
Controller with Diffamp
FeaTures
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DescripTion
PolyPhase® Controller Reduces Input and Output
The LTC®3856 is a single output, dual channel PolyPhase
synchronous step-down DC/DC controller that drives all
N-channel power MOSFET stages. This device includes a
high speed differential amplifier for remote output volt-
age sense. Power loss and supply noise are minimized by
operating the two controller output stages out-of-phase
and up to 12-phase operation can be achieved.
Capacitance and Power Supply Induced Noise
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Wide V Range: 4.5V to 38V Operation
IN
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±±.ꢀ5ꢁ% ±.ꢂV Reꢃerence Voltage Accuracy
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High Eꢃficiency: Up to 95ꢁ
Programmable Burst Mode® Operation or
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Stage Shedding™ ꢃor Highest Light Load Eꢃficiency
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Active Voltage Positioning (AVP)
The LTC3856 monitors the output current by sensing
the voltage drop across the output inductor (DCR) or by
using a sense resistor. DCR temperature compensation
maintains an accurate current sense threshold over a
broad temperature range. A constant-frequency, current
mode architecture allows a phase-lockable frequency of
up to 770kHz.
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R
SENSE
or DCR Current Sensing
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Programmable DCR Temperature Compensation
Phase-Lockable Fixed Frequency: 25±kHz to ꢀꢀ±kHz
True Remote Sense Diꢃꢃerential Amplifier
Dual N-Channel MOSFET Synchronous Drive
V
V
Range: 0.6V to 5V without Differential Amplifier
Range: 0.6V to 3.3V with Differential Amplifier
OUT
OUT
A wide 4.5V to 38V input supply range encompasses
most intermediate bus voltages and battery chemistries.
Burst Mode operation, continuous or Stage Shedding
modes are supported. A TK/SS pin shared by both chan-
nels ramps the output voltage during start-up.
L, LT, LTC, LTM, Linear Technology, the Linear logo, PolyPhase, Burst Mode and OPTI-LOOP
are registered trademarks and Stage Shedding is a trademark of Linear Technology Corporation.
All other trademarks are the property of their respective owners. Protected by U.S. Patents,
including 5481178, 5705919, 5929620, 6100678, 6144194, 6177787, 6304066, 6498466,
6580258, 6611131, 6674274.
Adjustable Soft-Start or V
Tracking
OUT
Stackable for Up to 12-Phase Operation
32-Pin (5mm × 5mm) QFN and 38-Pin TSSOP Packages
applicaTions
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Telecom and Datacom Systems
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Industrial and Medical Instruments
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DC Power Distribution Systems
Computer Systems
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Typical applicaTion
Eꢃficiency and Power Loss
vs Output Current
High Eꢃficiency 1.5V/5±A Step-Down Converter
V
100
90
100
10
1
IN
V
V
= 12V
4.5V TO
20V
IN
OUT
10µF
s 4
30.1k
= 1.5V
DIFFOUT
TG1
BOOST1
SW1
V
IN
S
0.33µH
S
Burst Mode
OPERATION
V
FB
0.1µF
80
ILIM
20k
LTC3856
S
70
RUN
BG1
S
S
PLLIN
PGOOD
CLKOUT
PHASMD
MODE
ITEMP
FREQ
60
50
+
SENSE1
–
SENSE1
TG2
BOOST2
SW2
40
30
20
10
0
S
0.33µH
V
1.5V
50A
OUT
0.1µF
S
S
S
0
BG2
122k
EXTV
INTV
S
S
CC
CC
+
100µF
s 8
DIFFN
DIFFP
SENSE2
SENSE2
4.7µF
–
–1
100
0.1
1
10
I
TH
TK/SS GND AVP ISET
2200pF
1.5k
LOAD CURRENT (A)
0.1µF
3856 TA01b
S
3856 TA01a
3856f
ꢀ