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., + d
2
V/dt
2
, and –
D
V) 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 –
D
V 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 (d
2
V/dt
2
).
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
Top-off charge stop
Fast charge stop
d
2
V
dt
2
)
without
charge control
–
D
V
preformation
1.6 V
I (R
B1)
95 10616
t
1
= 5 min
4 (17)
ÎÎ
–
D
V
)
ddtV , –
D
V
2
2
Fast charge rate I
O
Top-off
charge rate
1/4 I
O
t
2
= 20 min
Trickle
charge rate
1/256 I
O
t
Figure 3. Charge function diagram, f
osc
= 800 Hz
TELEFUNKEN Semiconductors
Rev. A2, 14-Nov-96
TEMIC [ TEMIC SEMICONDUCTORS ]
