6

ICS1712

Cells that are not thoroughly conditioned or possess an unusual cell

construction may not have a normal voltage profile. The ICS1712

uses an alternate method of charge termination based on a slight

decrease in the voltage slope to stop charge to cells whose voltage

profile is very shallow. This method looks for a flattening of the

voltage slope which may indicate a shallow peak in the voltage

profile. The zero slope point occurs slightly beyond the peak

voltage and is shown on the voltage curve graph.

Charge Termination Methods

Several charge termination schemes, including voltage slope,

temperature slope, maximum temperature and two overall charge

timers are available. The voltage slope and negative voltage slope

methods may be used with or without the temperature slope and the

maximum temperature method. Maximum temperature and the fast

charge timer are available as backup methods.

Voltage Slope Termination

The most distinctive point on the voltage curve of a charging

battery in response to a constant current is the voltage peak that

occurs as the cell approaches full charge. By mathematically

calculating the first derivative of the voltage, a second curve can be

generated showing the change in voltage with respect to time as

shown in Figure 6. The slope will reach a maximum just before the

actual peak in the cell voltage. Using the voltage slope data, the

ICS1712 calculates the point of full charge and accurately

terminates the applied current as the battery reaches that point. The

actual termination point depends on the charging characteristics of

the particular battery.

Figure 6: Voltage and slope curves showing inflection and zero slope points