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U2407B

Simple Controller for Fast Charge Systems

Temic Semiconductors 

U2407B

General Description

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

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 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.

Battery

voltage

5V

Battery insertion

preformation

1.6 V

ÎΖDVÎÎ

Fast charge stop

) d2V

dt2

Top-off charge stop

without

charge control

–DV

) D d2V

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

TELEFUNKEN Semiconductors

Rev. A4, 05-Mar-97

3 (16)

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