LM3647 Datasheet, PDF (5/17 Pages) National Semiconductor (TI) – Universal Battery Charger for Li-Ion, Ni-MH and Ni-Cd Batteries

4.0 Functional Description
4.1 General
The LM3647 can be configured to charge three different
types of batteries: Ni-Cd, Ni-MH and Li-Ion. The charger be-
havior for Ni-Cd and Ni-MH is similar but the charge curves
will appear slightly different due to the differences in chemis-
try. The Ni-Cd/Ni-MH charging algorithm is divided into four
phases:
Soft Start: The LM3647 detects that a battery is connected
and verifies that the temperature is within limit.
Charging starts with a current of 0.2C and switch-
es into next phase on timeout. Error termination
will be triggered by Maximum Battery Voltage
(CEL-pin > 3.017V) or if the battery voltage never
reaches the Defective Battery Level (CEL-pin <
1.2V).
Fast Charge: Constant current is applied to the battery and
the LM3647 monitors voltage and temperature
(optional). Switch into next phase will appear as a
voltage drop in the charging curve: (Ni-Cd ~
50mV/cell) and (Ni-MH ~ 17mV/cell). Error termi-
nation will be triggered by over-temperature.
Topping Charge: A current of 0.2C is applied to the battery
for a user defined time (RC network at SEL4)
Maintenance Charge: Is user selectable and is a fixed per-
centage of the Fast Charge rate.
Discharge before charge is user selectable.
Ni-Cd Charging Curve:
Voltage
Time
Discharge Soft Start Fast Charge
Topping
Charge
Maintenance
Charge
Ni-MH Charging Curve:
Voltage
Time
Discharge Soft Start Fast Charge
Topping
Charge
Maintenance
Charge
The Li-Ion charging algorithm is also divided into four phas-
es:
s Qualification: The LM3647 detects that a battery is con-
nected and verifies that the temperature (optional but
highly recommended for safety reasons) is within limit.
Charging starts with a current of 0.2C and switches into
next phase on timeout (~ 1 minute). Error termination will
be triggered if the battery voltage does not reach the Li-
Ion Battery Qualification Level (CEL-pin < 1.2V) within
one minute.
s Fast Charge Constant Current: Battery voltage will rise
until Maximum Battery Voltage (CEL-pin = 2.675V or
2.74V depending on SEL3) is reached.
s Fast Charge Constant Voltage: Keeps the voltage con-
stant until the current has decreased below the threshold
(CS at 2.3V).
s Maintenance Charge: Is user selectable and is a fixed
percentage of the Fast Charge rate.
Voltage
Current
Qualification Fast Charge
Fast Charge
Constant Current Constant Voltage
Maintenance
Charge
Time
4.2 Advanced Pin Descriptions
SEL1 is a selection pin to set the LM3647 in different charge
behavior. The pin has three states: tied to Vcc, GND, or un-
connected (Hi-Z). When the charger is configured to charge
Ni-Cd or Ni-MH batteries, this pin determines if the charger
discharges the battery before charging or if the charger shall
only maintenance charge the battery. When the charger is
configured for Li-Ion batteries, this pin determines how the
charger behaves during maintenance charge.
SEL2 is a selection pin to determine the battery type to be
charged. The pin has three states: tied to Vcc (Ni-MH), GND
(Ni-Cd), or unconnected (Li-lon).
SEL3 is a selection pin used to set charger hardware modes.
The pin has two states: tied to Vcc or GND. When configured
for Ni-Cd/Ni-MH batteries, this pin determines whether the
PWM is fast and has current feedback, or slow and has ex-
ternal current control. When configured for Li-Ion batteries,
this pin changes the regulation point for maximum voltage,
2.675V (4.1V Cell) or 2.74V (4.2V Cell).
Note: SEL3 must be hard wired to Vcc if a charger that sup-
ports both Li-Ion and Ni-Cd Ni-MH is implemented.
SEL4 is connected to a RC-network that determines the
charge time-outs. This RC-network is also connected to the
output LED1.
RCIN is a high-speed timing pin, used to drive the charger at
the right frequency connected to a RC-network.
GND is the ground pin.
Vcc is the power-supply pin. This pin should have a 100nF
capacitor tied to GND.
RESET is a reset pin.
LED1 is an active-low output used to indicate charge phase.
It is also used when measuring the charge timeout value.
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