The integrated circuit, U2402B, 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 identifica-
tions ( 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
U2402B-C takes into consideration the additional
changes in positive charge curves, according to the se-
cond 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 bat-
tery. 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 con-
trol results in very efficient switch-off.
An additional temperature control input increases not
only the performances of the charge switching character-
istics but also prevents the general charging of a battery
whose temperature is outside the specified window.
A constant charge current is necessary for continued
charge-voltage characteristic. This constant current regu-
lation is achieved with the help of internal amplifier phase
control and a simple shunt-current control technique.
All functions relating to battery management can be
achieved with dc-supply charge systems. A dc-dc-con-
verter or linear regulator should take over the function of
power supply. For further information please refer to the
t1 = 5 min
shorted batteries ignored
Fast charge rate IO
vt2 20 min
Figure 3. Charge function diagram, fosc = 800 Hz
Rev. A3, 14-Nov-96