LTC4015_15 Datasheet, PDF (27/76 Pages) Linear Technology – Multichemistry Buck Battery Charger Controller with Digital Telemetry System

LTC4015
Operation
Li-Ion/LiFePO₄ Battery Charger Operation
The LTC4015 provides full featured, inherently safe,
constant-current/constant-voltage Li-Ion/LiFePO₄ battery
charging. Features include battery presence detection,
automatic recharge, maximum charge time safety timer,
precharge (Li-Ion only), rapid absorb charge (LiFePO₄
only), programmable CV timer and C/x termination, therm-
istor temperature controlled charging, programmable
end-of-charge indication, programmable charge voltage,
programmable charge current, J.E.I.T.A. support, battery
series resistance measurement, detailed status reporting,
and programmable interrupt generation.
LTC4015 Charge Algorithm Overview
The LTC4015 charge algorithms are based on a constant-
current constant-voltage charging (CC-CV)technique. The
battery is charged at a constant-current (CC) until the
battery reaches its charge voltage (V_CHARGE) whereupon
the delivered charge current is automatically reduced to
maintain the battery at a constant V_CHARGE (CV).
Under voltage current limiting (UVCL) is used to automati-
cally reduce charge current to help keep V_IN from falling
below a minimum voltage. Input current limiting (ICL) is
used to automatically limit charge current to help keep
Input current below a maximum level. However, UVCL
and ICL can only reduce charge current. The total load
current from V_IN cannot be limited by the LTC4015 if the
load on the system exceeds the ICL setpoint.
Li-Ion Charge Algorithm Overview
(See Figure 5A for Li-Ion battery charging state diagram)
The charge algorithm begins with a battery detection test
and proceeds to constant-current constant-voltage (CC-
CV) charging. If the Li-Ion battery voltage is very low the
charger will charge at a reduced (precharge) CC rate until
the battery voltage reaches an acceptable level. Then it will
be charged at the full CC rate. CC-CV charging continues
until the charge cycle terminates based on time (default)
or battery current (C/x for Li-Ion programmable option).
LiFePO4 Charge Algorithm (without Absorption
Phase) Overview
(See Figure 5B for LiFePO₄ battery charging state diagram)
The charge algorithm begins with a battery detection test
and proceeds to constant-current constant-voltage (CC-
CV) charging. CC-CV charging continues until the charge
cycle terminates based on time in CV mode (default) or
battery current (C/x for LiFePO₄ programmable option).
Remaining in constant-voltage mode without termination
is also a LiFePO₄ programmable option.
LiFePO4 Charge Algorithm (with Absorption Phase)
Overview
(See Figure 5B for Li-FePO₄ battery charging state diagram)
An absorb phase can allow accelerated charging by raising
the charge voltage, which may result in a higher CC rate,
for a portion of the charge cycle. The charge algorithm
begins with a battery detection test and proceeds to CC-CV
charging with a charge voltage of V_ABSORB, which is an
absorb delta added to V_CHARGE. CC-CV absorption charging
continues until the V_ABSORB is reached and charge current
has dropped below the C/x threshold, or the maximum
absorb phase time has passed. Upon exiting the absorb
phase the charge voltage is reduced from V_ABSORB to
V_CHARGE. CC-CV charging continues until the charge cycle
terminates based on time in CV mode (default) or charge
current (C/x) (LiFePO₄ programmable option). Remaining
in constant-voltage mode without termination is also a
LiFePO₄ programmable option.
For more information www.linear.com/LTC4015
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