The integrated circuit, U2407B, 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
U2407B 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
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 is
generated from an external power supply and can be regu-
lated with the help of an internal op-amp regulator
(figure 2). An external current source can also be con-
trolled by the switch output Pin 16 (see figure 12).
For further information please refer to the applications.
Fast charge stop
Top-off charge stop
t1 = 5 min
Fast charge rate IO
t2 = 20 min
Figure 3. Charge function diagram, fosc = 800 Hz
Rev. A4, 05-Mar-97