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U2405B
Fast Charge Controller for Drained NiCd/NiMH Batteries
Description
The fast-charge battery controller circuit, U2405B, uses
bipolar technology. The IC enables the designer to create
an efficient and economic charge system. The U2405B
incorporates intelligent multiple-gradient battery-
voltage monitoring and mains phase control for power
management. With automatic top-off charging, the
Features
D Preformation algorithm for drained batteries
D Multiple gradient monitoring
D Temperature window (Tmin/Tmax)
D Exact battery voltage measurement without charge
D Phase control for charge-current regulation
D Top-off and trickle charge function
D Two LED outputs for charge status indication
D Disabling of d2V/dt2 switch-off criteria
during battery formation
D Battery-voltage check
18 (20) 17 (19) 16 (18)
14 (15)
integrated circuit ensures that the charge device stops
regular charging before the critical stage of overcharging
is achieved. It incorporates an additional algorithm for
reactivating fully drained batteries especially after long-
time storage. It has two LED driver indications for charge
and temperature status.
Applications
D Portable power tools
D Laptop/notebook personal computer
D Cellular/cordless phones
D Emergency lighting systems
D Hobby equipment
D Camcorder
Package: DIP18, SO20
13 (14)
12 (13) 11 (12)
4 (4)
1 (1)
Sync
ö
C
ö
R
Phase control
Vöi
Trigger output
Power - on control
VRef
6.5 V/10 mA
Oscillator
Control unit
Gradient
d2V/dt2 and –dV
15 (17)
2 (2)
Power supply
VS = 8 to 26 V
160 mV
Ref
Temp. control
Tmax Sensor
94 8585
5 (5) 6 (6)
7 (8) 8 (9)
Figure 1. Block diagram
Status control
Scan path
Battery
detection
VRef = 5 V
VBatt Monitor
0.1 to 4 V
3 (3)
10 (11)
Charge break
output
9 (10)
( ) SO 20, Pins 7 and 16 NC
TELEFUNKEN Semiconductors
Rev. A2, 14-Nov-96
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U2405B
Pin Description
Package: DIP18
Output 1
GND 2
LED2 3
Vöi 4
OPO 5
OPI 6
Tmax 7
Sensor 8
tp 9
93 7723 e
Package: SO20
Output 1
GND 2
LED2 3
Vöi 4
OPO 5
OPI 6
NC 7
Tmax 8
Sensor 9
tp 10
94 8594
2 (17)
18 Vsync
17
ö
C
16
ö
R
15 VS
14 VRef
13 Osc
12 STM.
11 LED1
10 VBatt
20 Vsync
19
ö
C
18
ö
R
17 VS
16 NC
15 VRef
14 Osc
13 STM.
12 LED1
11 VBatt
Pin Symbol
Function
1 Output Trigger output
2 GND Ground
3 LED2 Display output “Green”
4 Vöi Phase angle control input voltage
5 OPO Operational amplifier output
6 OPI Operational amplifier input
7 Tmax Maximum temperature
8 Sensor Temperature sensor
9 tp Charge break output
10 VBatt Battery voltage
11 LED1 LED display output “Red”
12 STM. Test mode switch (status control)
13 Osc Oscillator
14 VRef Reference output voltage
15 VS Supply voltage
16
ö
R
Ramp current adjustment –
resistance
17
ö
C
Ramp voltage – capacitance
18 Vsync. Mains synchronization input
Pin Symbol
Function
1 Output Trigger output
2 GND Ground
3 LED2 Display output “Green”
4 Vöi Phase angle control input voltage
5 OPO Operational amplifier output
6 OPI Operational amplifier input
7 NC Not connected
8 Tmax Maximum temperature
9 Sensor Temperature sensor
10 tp Charge break output
11 VBatt Battery voltage
12 LED1 LED display output “Red”
13 STM. Test mode switch (status control)
14 Osc Oscillator
15 VRef Reference output voltage
16 NC Not connected
17 VS Supply voltage
18
ö
R
Ramp current adjustment –
resistance
19
ö
C
Ramp voltage – capacitance
20 Vsync. Mains synchronization input
TELEFUNKEN Semiconductors
Rev. A2, 14-Nov-96

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U2405B
Figure 2. Block diagram with external circuit (DIP pinning)
TELEFUNKEN Semiconductors
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U2405B
General Description
The integrated circuit, U2405B, is designed for charging
Nickel-Cadmium (NiCd) and Nickel-Metal-Hydride
(NiMH) batteries. Fast charging results in voltage lobes
when fully charged (figure 3). It supplies two
identifications ( i. e., + d2V/dt2, and – DV ) to end the
charge operation at the proper time.
As compared to the existing charge concepts where the
* *charge is terminated after voltage lobes according
to – DV and temperature gradient identification, the
U2405B takes into consideration the additional changes
in positive charge curves, according to the second
derivative of the voltage with respect to time (d2V/dt2).
The charge identification is the sure method of switching
off the fast charge before overcharging the battery. This
helps to give the battery a long life by hindering any
marked increase in cell pressure and temperature.
Even in critical charge applications, such as a reduced
charge current or with NiMH batteries where weaker
charge characteristics are present multiple gradient
control results in very efficient switch-off.
An additional temperature control input increases not
only the performances of the charge switching
characteristics but also prevents the general charging of
a battery whose temperature is outside the specified
window.
A specific preformation algorithm is implemented for
reactivating fully drained batteries especially in the case
of batteries that have been stored for a long time.
A constant charge current is necessary for continued
charge-voltage characteristic. This constant current
regulation is achieved with the help of internal amplifier
phase control and a simple shunt-current control tech-
nique.
All functions relating to battery management can be
achieved with DC-supply charge systems. A DC-DC-
converter or linear regulator should take over the function
of power supply. For further information please refer to
the applications.
Battery
voltage
5V
Battery insertion
preformation
ÎÎ1.6 V
DV
Fast charge stop
) d2V
dt2
Top-off charge stop
without
charge control
DV
) Dd2V
dt2
,
V
I (RB1)
95 10616
t1 = 5 min
Fast charge rate IO
Top-off
charge rate
1/4 IO
t2 = 20 min
Figure 3. Charge function diagram, fosc = 800 Hz
Trickle
charge rate
1/256 IO
t
4 (17)
TELEFUNKEN Semiconductors
Rev. A2, 14-Nov-96

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U2405B
Flow Chart Explanation, fosc = 800 Hz
(Figures 2, 3 and 4)
Battery pack insertion disables the voltage lock at battery
detection input Pin 10. All functions in the integrated
circuit are reset. For further description, DIP-pinning is
taken into consideration.
Battery Insertion and –DV
Monitoring
After battery insertion fast charge Io begins when the
input voltage VBatt is higher than 1.6 V. For the first
5 minutes the d2V/dt2-gradient recognition is suppressed,
DV monitoring is activated. In case the detected VBatt
voltage is less then 1.6 V, the special preformation
procedure will be activated. The reference level with
respect to the cell voltage can be adjusted by the resistor
RB3 (see figure 2).
Preformation Procedure
Before fast charge of fully drained or long time stored
batteries begin, a reactivation is necessary. The
preformation current is dependent on pull-up resistor
RB1. The fast charge starts only after the VBatt is higher
than 1.6 V level. During the first 10 minutes the green
LED2 is blinking. If, after 10 minutes, VBatt voltage has
not reached the reference level, the indication changes to
red blinking LED1. The charge will continue with
preformation rate I (RB1). In case VBatt increases to 1.6 V
reference level, the fast charge rate current, Io, is
switched-on and the green LED2 is blinking.
DV Cut-Off (Monitoring)
When the signal at Pin 10 of the DA converter is 12 mV
below the actual value, the comparator identifies it as a
voltage drop of –DV. The validity of –DV cut-off is
considered only if the actual value is below 12 mV for
three consecutive cycles of measurement.
d2V/dt2-Gradient
If there is no charge stop within the first 5 minutes after
battery insertion, then d2V/dt2 monitoring will be active.
In this actual charge stage, all stop-charge criteria are
active.
When close to the battery’s capacity limit, the battery
voltage curve will typically rise. As long as the +d2V/dt2
stop-charging criteria are met, the device will stop the fast
charge activities.
Top-Off Charge Stage
By charge disconnection through the + d2V/dt2 mode, the
device switches automatically to a defined protective
top-off charge with a pulse rate of 1/4 IO (pulse time,
tp = 5.12 s, period, T = 20.48 s).
The top-off charge time is specified for a time of
20 minutes @ 800 Hz.
Trickle Charge Stage
When top-off charge is terminated, the device switches
automatically to trickle charge with 1/256 IO (tp = 5.12 s,
period = 1310.72 s). The trickle continues until the
battery pack is removed.
Basic Description
Power Supply, Figure 2
The charge controller allows the direct power supply of
8 to 26 V at Pin 15. Internal regulation limits higher input
voltages. Series resistance, R1, regulates the supply
current, IS, to a maximum value of 25 mA. Series
resistance is recommended to suppress the noise signal,
even below 26 V limitation. It is calculated as follows.
wR1min
Vmax–26 V
25 mA
vR1max
Vmin– 8 V
Itot
where
Itot = IS + IRB1 + I1
Vmax, Vmin = Rectified voltage
IS = Current consumption (IC) without load
IRB1 = Current through resistance, RB1
I1 = Trigger current at Pin 1
TELEFUNKEN Semiconductors
Rev. A2, 14-Nov-96
5 (17)