LTC3855_15 Datasheet, PDF (1/44 Pages) Linear Technology – Dual, Multiphase Synchronous DC/DC Controller with Differential Remote Sense

LTC3855
Dual, Multiphase
Synchronous DC/DC Controller
with Differential Remote Sense
Features
n _{Dual, 180° Phased Controllers Reduce Required}
Input Capacitance and Power Supply Induced Noise
n _{High Efficiency: Up to 95%}
n _{RSENSE 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 VIN Range: 4.5V to 38V}
n _{VOUT Range: 0.6V to 12.5V without Differential Amplifier}
n _{VOUT 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 VOUT Tracking}
n _{Foldback Output Current Limiting}
n _{Output Overvoltage Protection}
n _{40-Pin (6mm × 6mm) QFN and 38-Lead FE Packages}
Applications
n _{Computer Systems}
n _{Telecom Systems}
n _{Industrial and Medical Instruments}
n _{DC Power Distribution Systems}
Description
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.
Typical Application
High Efficiency Dual 1.8V/1.2V Step-Down Converter
0.56µH
V_OUT1
1.8V
15A
+
40.2k
330µF
×2
+
4.7µF
0.1µF
V_IN
TG1
BOOST1
SW1
INTV_CC
TG2
BOOST2
SW2
BG1
BG2
PGND1
SENSE1⁺
SENSE1^–
LTC3855
PGND2
FREQ
SENSE2⁺
SENSE2^–
DIFFOUT
V_FB1
V_FB2
I_TH1
I_TH2
470pF _{TK/SS1 DIFFP SGND DIFFN TK/SS2}
20k
15k _0.1µF
0.1µF
1µF
0.1µF
20k
470pF
100k ^7.5k
20k
22µF
V_IN
4.5V TO
20V
0.4µH
Load Step
(Forced Continuous Mode)
I_LOAD
5A/DIV
300mA TO 5A
I_L
5A/DIV
V_OUT2
1.2V
15A
+ _330µF
×2
3855 TA01
V_OUT
100mV/DIV
AC-COUPLED
V_IN = 12V
V_OUT = 1.8V
50µs/DIV
3855 TA01a
3855f