LTC3871/LTC3871-1
Bidirectional PolyPhase
Synchronous Buck or Boost Controller
FEATURES
nn Unique Architecture Allows Dynamic Regulation of
Input Voltage, Output Voltage or Current
nn VHIGH Voltages Up to 100V
nn VLOW Voltages Up to 30V
nn Synchronous Rectification: Up to 97% Efficiency
nn ADI-Proprietary Advanced Current Mode Control
nn ±1% Voltage Regulation Accuracy Over Temperature
nn Accurate, Programmable Output Current Monitoring
and Regulation for Both Buck and Boost Operation
nn Selectable Buck and Boost Current Sense Limits
nn Programmable DRVCC/EXTVCC Optimizes Efficiency
nn Programmable VHIGH UV and OV Thresholds
nn Programmable VLOW OV Threshold
nn Phase-Lockable Frequency: 60kHz to 460kHz
nn Multiphase/Multi-ICs Operation Up to 12 Phases
nn Selectable CCM/DCM Modes
nn Thermally Enhanced 48-Lead LQFP Package
APPLICATIONS
nn Automotive 48V/12V Dual Battery Systems
nn Backup Power Systems
DESCRIPTION
The LTC®3871/LTC3871-1 is a high performance bidi-
rectional buck or boost switching regulator controller
that operates in either buck or boost mode on demand.
It regulates in buck mode from VHIGH-to-VLOW and boost
mode from VLOW-to-VHIGH depending on a control signal,
making it ideal for 48V/12V automotive dual battery sys-
tems. An accurate current programming loop regulates
the maximum current that can be delivered in either direc-
tion. The LTC3871/LTC3871-1 allows both batteries to
supply energy to the load simultaneously by converting
energy from one battery to the other.
Its proprietary constant-frequency current mode
architecture enhances the signal-to-noise ratio enabling
low noise operation and provides excellent current
matching between phases. Additional features include
discontinuous or continuous mode of operation, OV/UV
monitors, independent loop compensation for buck and
boost operation, accurate output current monitoring and
overcurrent protection. The LTC3871 and LTC3871-1
have different current limit foldback characteristics.
All registered trademarks and trademarks are the property of their respective owners.
TYPICAL APPLICATION
High Efficiency Bidirectional Charger/Power Supply
VHIGH
26V TO 58V
OVHIGH
UVHIGH
EXTVCC
VFBLOW
BUCK BOOST
VLOW
ITHHIGH
ITHLOW
SS
SNS1–
SNSD1+
SNSA1+
BST1
LTC3871/
TG1
LTC3871-1
SW1
BG1
BUCK
IMON
FREQ
OVLOW
DRVCC
V5
VFBHIGH
SNS2–
SNSD2+
SNSA2+
BST2
TG2
SW2
BG2
3871 TA01a
DRVCC
DRVCC
BUCK
VLOW
12V
BATTERY
VLOW
5V/DIV
IL
5A/DIV
VHIGH
10V/DIV
SW
50V/DIV
PINS NOT SHOWN IN THIS CIRCUIT:
CLKOUT, DRVSET, FAULT, ILIM, MODE,
PHSMD, RUN, SETCUR AND SYNC.
Document Feedback
For more information www.analog.com
Buck-to-Boost Transition
BUCK BOOST
50μ/DIV
3871 TA01b
Rev. B
1
