LM3647 Datasheet, PDF (9/17 Pages) National Semiconductor (TI) – Universal Battery Charger for Li-Ion, Ni-MH and Ni-Cd Batteries

CURRENT-LIMITER
PWM
R6
10k
R22
10k
R5
10k
C9
1uF
DC-PWM
C1
C2
1uF
1uF
Slow PWM-mode:
The PWM-pin turns the external current source on and off at
a rate of 0.1Hz. (This example is just one of many possible
design solutions.) The PWM-pin (SLOW_PWM) turns the
transistor Q1 on and off. When the transistor is off the current
source is on, and when the transistor is on the current source
is off (V_OUT at approximate 0.7V). The value of R1 de-
pends on the size of the charge current (see formula):
I _out =
1.25 - V_d
R1
V_d = Voltage Drop Across D1
The PWM duty cycle for the different charge cycles are listed
below:
Charge Phase:
Soft Start
Fast Charge
Topping Charge
Maintenance Charge
PWM Duty Cycle:
10%
100%
10%
5%
4.3.9 User Interface
The user interface consists of three LEDs and one buzzer.
The LEDs have four different states:
On, off, slow flash (~1 Hz) and fast flash (~10 Hz). The buzz-
er has three different states: off, one short beep (~100ms)
and one long beep (~1s).
The user interface is designed in a flexible way. Use of the
buzzer or the LEDs is optional, depending on design require-
ments. It is possible to use the LM3647 with one, two or all
three LEDs.
A single Charged Status LED can be implemented with a 2-
input NAND gate on LED1 and LED3. In this implemention,
note that a pull-up resistor is required on LED1 and LED3.
Ni-Cd/Ni-MH User Interface Scheme
Charge phase
No battery
New battery / Temp-test
Softstart charge
Charging
Topping charge
Maintenance
Discharge
Temperature error
Error
LED1 status
Off
Fast flash
Slow flash
On
On
On
Off
2 Fast flashes
Fast flash
LED2 status
Off
Off
Off
Slow flash
Fast flash
Off
Slow flash
Off
Off
LED3 status
Off
Off
Off
Off
Off
On
Off
On
Fast flash
Buzzer status
Off
Short beep
Off
Off
Off
Long beep
Off
Short beep
Short beep
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