LTC3856_15 Datasheet, PDF (1/40 Pages) Linear Technology – 2-Phase Synchronous Step-Down DC/DC Controller with Diffamp

Features
n _PolyPhase^® _{Controller Reduces Input and Output}
Capacitance and Power Supply Induced Noise
n _{Wide VIN Range: 4.5V to 38V Operation}
n _{±0.75%, 0.6V Reference Voltage Accuracy}
n _{High Efficiency: Up to 95%}
n _{Programmable Burst Mode}^® _{Operation or}
Stage Shedding™ for Highest Light Load Efficiency
n _{Active Voltage Positioning (AVP)}
n _{RSENSE or DCR Current Sensing}
n _{Programmable DCR Temperature Compensation}
n _{Phase-Lockable Fixed Frequency: 250kHz to 770kHz}
n _{True Remote Sense Differential Amplifier}
n _{Dual N-Channel MOSFET Synchronous Drive}
n _{VOUT Range: 0.6V to 5V without Differential Amplifier}
n _{VOUT Range: 0.6V to 3.3V with Differential Amplifier}
n _{Adjustable Soft-Start or VOUT Tracking}
n _{Stackable for Up to 12-Phase Operation}
n _{32-Pin (5mm × 5mm) QFN and 38-Pin TSSOP Packages}
Applications
n _{Telecom and Datacom Systems}
n _{Industrial and Medical Instruments}
n _{DC Power Distribution Systems}
n _{Computer Systems}
LTC3856
2-Phase Synchronous
Step-Down DC/DC
Controller with Diffamp
Description
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.
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.
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.
Typical Application
High Efficiency 1.5V/50A Step-Down Converter
30.1k
20k
DIFFOUT V_IN
TG1
V_FB
BOOST1
ILIM _LTC3856 SW1
RUN
BG1
PGOOD
CLKOUT
PHASMD
PLLIN
SENSE1⁺
SENSE1^–
MODE
TG2
ITEMP
BOOST2
FREQ
SW2
122k
EXTV_CC
DIFFN
DIFFP
BG2
INTV_CC
SENSE2⁺
SENSE2^–
I_TH TK/SS GND AVP ISET
2200pF
1.5k ^0.1µF
3856 TA01a
0.1µF
0.1µF
4.7µF
0.33µH
0.33µH
V_IN
10µF ^{4.5V TO}
s4 ^20V
V_OUT
1.5V
50A
100µF
s8
Efficiency and Power Loss
vs Output Current
100
100
V_IN = 12V
90 V_OUT = 1.5V
80
Burst Mode
OPERATION
10
70
60
50
1
40
30
0
20
10
0
0.1
1
–1
10
100
LOAD CURRENT (A)
3856 TA01b
3856f