LTC3855
Dual, Multiphase
Synchronous DC/DC Controller
with Differential Remote Sense
FeaTures
DescripTion
TheLTC®3855isadualPolyPhase® currentmodesynchro-
n
Dual, 180° Phased Controllers Reduce Required
Input Capacitance and Power Supply Induced Noise
High Efficiency: Up to 95%
SENSE
Programmable DCR Temperature Compensation
0ꢀ.5% 0ꢀꢁ6 ꢂutput 6oltage Accuracy
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,
50mVor75mV, allowingtheuseofeithertheinductorDCR
or a discrete sense resistor as the sensing element.
n
n
n
n
n
n
n
n
n
n
n
n
n
n
n
R
or DCR Current Sensing
Phase-Lockable Fixed Frequency 250kHz to ..0kHz
True Remote Sensing Differential Amplifier
Dual N-Channel MOSFET Synchronous Drive
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
noiseareminimizedbyoperatingthetwocontrolleroutput
stages out of phase. Burst Mode® operation, continuous
or pulse-skipping modes are supported.
Wide V Range: 4.5V to 38V
IN
V
V
Range: 0.6V to 12.5V without Differential Amplifier
Range: 0.6V to 3.3V with Differential Amplifier
OUT
OUT
Clock Input and Output for Up to 12-Phase Operation
Adjustable Soft-Start or V
Tracking
OUT
Foldback Output Current Limiting
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.
Output Overvoltage Protection
40-Pin (6mm × 6mm) QFN and 38-Lead FE Packages
applicaTions
n
Computer Systems
n
Telecom Systems
n
Industrial and Medical Instruments
DC Power Distribution Systems
n
Typical applicaTion
High Efficiency Dual 1ꢀ86/1ꢀ26 Step-Down Converter
V
IN
Load Step
(Forced Continuous Mode)
4.5V TO
20V
+
22µF
1µF
4.7µF
V
IN
INTV
CC
TG1
TG2
I
LOAD
0.1µF
0.1µF
5A/DIV
BOOST1
SW1
BOOST2
SW2
0.4µH
0.56µH
300mA TO 5A
BG1
BG2
I
L
PGND1
PGND2
FREQ
5A/DIV
LTC3855
+
+
SENSE1
SENSE1
SENSE2
–
–
SENSE2
V
OUT
20k
V
100mV/DIV
OUT1
1.8V
15A
V
DIFFOUT
OUT2
AC-COUPLED
V
FB1
1.2V
V
FB2
15A
40.2k
I
I
TH1
TK/SS1 DIFFP SGND DIFFN TK/SS2
TH2
470pF
470pF
7.5k
20k
+
+
330µF
×2
330µF
×2
3855 TA01a
20k
100k
15k
50µs/DIV
0.1µF
0.1µF
V
V
= 12V
IN
OUT
= 1.8V
3855 TA01
3855f
ꢀ