LM3647 datasheet(5/17 Pages) NSC

5 / 17 page

www.national.com

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:

Ni-MH Charging Curve:

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.

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.

Voltage

Time

Discharge

Soft Start

Fast Charge

Topping

Charge

Maintenance

Charge

Voltage

Time

Discharge

Soft Start

Fast Charge

Topping

Charge

Maintenance

Charge

Voltage

Time

Qualification

Fast Charge

Constant Current

Fast Charge

Constant Voltage

Maintenance

Charge

Current

LM3647 Datasheet(PDF) 5 Page - National Semiconductor (TI)

LM3647 Datasheet(HTML) 5 Page - National Semiconductor (TI)

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17

Datasheet Download

Link URL