Datasheet

bq78PL116
SLUSAB8B –OCTOBER 2010– REVISED FEBRUARY 2011 www.ti.com
OPERATION
The bq78PL116 battery-management controller serves as a master controller for a Li-Ion battery system
consisting of up to 16 cells in series. Any number of cells may be connected in parallel; other system or safety
issues limit the number of parallel cells. The bq78PL116 provides extraordinarily precise state-of-charge gas
gauging along with first- and second-level pack safety functions. Voltage and current measurements are
performed synchronously and simultaneously for all cells in the system, allowing a level of precision not
previously possible in battery management. Temperature is measured by up to four additional external
temperature sensors. Coulomb counting is captured continuously by a dedicated 18-bit integrating delta-sigma
ADC in the bq78PL116. The CPU in the bq78PL116 is also responsible for system data calculations and
communicating parameters via the SMBus interface.
PowerLAN Communication Link
PowerLAN technology is Texas Instruments’ patented serial network and protocol designed specifically for
battery management in a multicell system environment. The PowerLAN link is used to initiate and report
measurements of cell voltage and temperature, and control cell balancing. The bq78PL116 serves as the master
controller of the PowerLAN link and can interface to multiple bq76PL102 dual-cell battery monitors, which
measure and balance additional cells. The bq78PL116 monitors the first three or four cells, and bq76PL102s can
be added to monitor more series cells.
The PowerLAN link isolates voltages from adjacent bq76PL102 devices to permit high-voltage stack assembly
without compromising precision and accuracy. The PowerLAN link is expandable to support up to 16 cells in
series. Each bq76PL102 handles voltage and temperature measurements, as well as balancing for two cells. The
PowerLAN link provides high ESD tolerance and high immunity to noise generated by nearby digital circuitry or
switching currents. Each bq76PL102 has both a PowerLAN input and PowerLAN output: Received data is
buffered and retransmitted, permitting high numbers of nodes without loss of signal fidelity. Signals are
capacitor-coupled between nodes, providing dc isolation.
Safety
Unique in the battery-management controller market, the bq78PL116 simultaneously measures voltage and
current using independent and highly accurate delta-sigma ADCs. This technique removes virtually all systemic
noise from measurements, which are made during all modes of battery operation: charge, discharge, and rest.
The bq78PL116 also directs all connected bq76PL102 dual-cell battery monitors to measure each cell voltage
simultaneously with the bq78PL116 measurements. Battery impedance and self-discharge characteristics are
thus measured with an unprecedented level of accuracy in real time. The bq78PL116 applies this precise
information to SmartSafety algorithms to detect certain anomalies and conditions which may be indicative of
internal cell faults, before they become serious problems.
The bq78PL116 uses its enhanced measurement system to detect system faults including cell under- and
overvoltage, cell under- and overtemperature, system overvoltage, and system overcurrent. First-level safety
algorithms first attempt to open the MOSFET safety switches. If this fails, second-level safety algorithms activate
the SPROT output, normally used to open a fuse and provide permanent, hard protection for the systems.
External MOSFET control inputs with programmable polarity can also be used to operate the safety MOSFETs
under control of user supplied circuitry. The bq78PL116 continuously monitors these inputs. If any MOSFET fails
to open when commanded; the 2
nd
level safety algorithms also activate the SPROT output. All first- and
second-level safety algorithms have fully programmable time delays to prevent false triggering.
Cell Balancing
Patented PowerPump cell balancing technology drastically increases the useful life of battery packs by
eliminating the cycle life fade of multi-cell packs due to cell imbalance. PowerPump technology efficiently
transfers charge from cell to cell, rather than simply bleeding off charging energy as heat as is typically done with
resistive-bleed balancing circuits. Balancing is configurable and may be performed during any battery operational
modes: charge, discharge, or rest. Compared to resistive bleed balancing, virtually no energy is lost as heat. The
actual balance current is externally scalable and can range from 10 mA to 1 A (100 mA typical) depending on
component selection and system or cell requirements.
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