Datasheet

LTC3855
1
3855f
Typical applicaTion
DescripTion
Dual, Multiphase
Synchronous DC/DC Controller
with Differential Remote Sense
The LTC
®
3855 is a dual PolyPhase
®
current mode synchro-
nous step-down switching regulator controller that drives
all N-channel power MOSFET stages. It includes a high
speed differential remote sense amplifier. The maximum
current sense voltage is programmable for either 30mV,
50mV or 75mV, allowing the use of either the inductor DCR
or a discrete sense resistor as the sensing element.
The LTC3855 features a precision 0.6V reference and can
produce output voltages up to 12.5V. A wide 4.5V to 38V
input supply range encompasses most intermediate bus
voltages and battery chemistries. Power loss and supply
noise are minimized by operating the two controller output
stages out of phase. Burst Mode
®
operation, continuous
or pulse-skipping modes are supported.
The LTC3855 can be configured for up to 12-phase op-
eration, has DCR temperature compensation, two power
good signals and two current limit set pins. The LTC3855
is available in low profile 40-pin 6mm × 6mm QFN and
38-lead exposed pad FE packages.
L, LT, LTC, LTM, Linear Technology, the Linear logo, Burst Mode and PolyPhase are registered
trademarks 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, 6580258.
FeaTures
applicaTions
n
Dual, 180° Phased Controllers Reduce Required
Input Capacitance and Power Supply Induced Noise
n
High Efficiency: Up to 95%
n
R
SENSE
or DCR Current Sensing
n
Programmable DCR Temperature Compensation
n
±0.75% 0.6V Output Voltage Accuracy
n
Phase-Lockable Fixed Frequency 250kHz to 770kHz
n
True Remote Sensing Differential Amplifier
n
Dual N-Channel MOSFET Synchronous Drive
n
Wide V
IN
Range: 4.5V to 38V
n
V
OUT
Range: 0.6V to 12.5V without Differential Amplifier
n
V
OUT
Range: 0.6V to 3.3V with Differential Amplifier
n
Clock Input and Output for Up to 12-Phase Operation
n
Adjustable Soft-Start or V
OUT
Tracking
n
Foldback Output Current Limiting
n
Output Overvoltage Protection
n
40-Pin (6mm × 6mm) QFN and 38-Lead FE Packages
n
Computer Systems
n
Telecom Systems
n
Industrial and Medical Instruments
n
DC Power Distribution Systems
High Efficiency Dual 1.8V/1.2V Step-Down Converter
0.1µF
40.2k
0.56µH
470pF
1µF
22µF
330µF
×2
20k
15k
V
OUT1
1.8V
15A
0.1µF
0.4µH
470pF
330µF
×2
20k
7.5k
100k
V
OUT2
1.2V
15A
TG1 TG2
BOOST1 BOOST2
SW1 SW2
BG1
BG2
DIFFP
PGND2
FREQ
SENSE1
+
SENSE2
+
DIFFOUT
SENSE1
SENSE2
V
FB1
V
FB2
I
TH1
I
TH2
V
IN
INTV
CC
TK/SS1 TK/SS2
V
IN
4.5V TO
20V
3855 TA01
DIFFNSGND
0.1µF
0.1µF
LTC3855
PGND1
4.7µF
+
++
20k
Load Step
(Forced Continuous Mode)
V
IN
= 12V
V
OUT
= 1.8V
50µs/DIV
3855 TA01a
I
L
5A/DIV
V
OUT
100mV/DIV
AC-COUPLED
I
LOAD
5A/DIV
300mA TO 5A

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