LTC4015_15 Datasheet, PDF (17/76 Pages) Linear Technology – Multichemistry Buck Battery Charger Controller with Digital Telemetry System

LTC4015
Operation
Introduction
The LTC4015 is a Li-Ion/LiFePO₄/lead-acid battery charger
utilizing a step-down switching controller. It is designed
to efficiently transfer power from a variety of possible
sources, such as wall adapters and solar panels, to a
battery and system load while minimizing power dissi-
pation and easing thermal budgeting constraints. Since
a switching regulator conserves power, the LTC4015
allows the charge current to exceed the source's output
current, making maximum use of the allowable power for
battery charging without exceeding the source's delivery
specifications. By incorporating input voltage and current
measurement and control systems, the switching charger
interfaces seamlessly to these sources without requiring
application software to monitor and adjust system loads.
By decoupling the system load from the battery and pri-
oritizing power to the system, the instant-on PowerPath
architecture ensures that the system is powered immediately
after V_IN is applied, even with a completely dead battery.
Two ideal diode controllers drive external MOSFETs to
provide low loss power paths from V_IN and V_BAT to the
system. Two ideal diodes work with the charger to provide
power from V_BAT to the system without back driving V_IN.
The ideal diode from V_BAT to the system load guarantees
that power is available to the system even if there is insuf-
ficient or absent power from V_IN. The ideal diode from V_IN
to the system load guarantees neither V_BAT or the system
will back drive V_IN.
A wide range of input current settings as well as battery
charge current settings are available by software control
and the values of sense resistors R_SNSI and R_SNSB. A
measurement subsystem periodically monitors and re-
ports system parameters via the I²C serial port. Included
in this subsystem is a Coulomb counter to allow battery
gas gauging.
An interrupt subsystem can be enabled to alert the host
microprocessor of various status change events so that
system parameters can be varied as needed by the system.
Many status change events are maskable for maximum
flexibility.
To eliminate battery drain between manufacture and sale,
a ship-and-store feature reduces the already low battery
drain and optionally disconnects power from downstream
circuitry.
The input undervoltage current loop (UVCL) can be engaged
to help keep the input voltage from decreasing beyond a
minimum voltage when a resistive cable or power limited
supply such as a solar panel is providing input power to
the LTC4015. A maximum power point algorithm using this
control loop has been preprogrammed into the LTC4015
to maximize power extraction from solar panels and other
resistive sources.
Finally, the LTC4015 has a digital subsystem that provides
substantial adjustability so that power levels and status
information can be controlled and monitored via the simple
2-wire I²C serial port.
LTC4015 Digital System Overview
The LTC4015 contains an advanced digital system which
can be optionally accessed using the I²C serial port. The
LTC4015 digital system can be used extensively in the
application or not at all, as dictated by the application
requirements. This data sheet provides extensive details
of the digital functions of the LTC4015, though much of
this detail is not required for simpler applications.
Use of the serial port is completely optional. Even without
use of the serial port, the LTC4015 is a fully functioning high
performance battery charger which is highly configurable
using external components and pin connections. Chem-
istry/algorithm, cell count, charge current, input current
regulation (ICL), V_IN undervoltage regulation (UVCL),
maximum power point tracking (MPPT), and switching
charger frequency and compensation are all externally
configurable without using the serial port.
For applications requiring the LTC4015’s advanced digital
features, the serial port provides a means to use the Cou-
lomb counter, read status and ADC telemetry data from
the measurement system, monitor charger operation,
configure charger settings (e.g. charge voltage, charge
current, temperature response, etc), enable/disable/read/
clear alerts, activate low power ship mode, and enable/
disable the battery charger.
Detailed information about the digital system and the serial
port registers, as well as digital system usage examples,
can be found in the section LTC4015 Digital System.
4015f
For more information www.linear.com/LTC4015
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