ICS1722 datasheet(6/24 Pages) GALAXY

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ICS1722

Cells that are not thoroughly conditioned or possess an unusual cell

construction may not have a normal voltage profile. The ICS1722

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 Timer Termination

The controller uses a timer to limit the fast charge duration.

These times are pre-programmed, and are automatically adjusted in

time duration according to the charge rate selected. Fast charge

timer termination is a safety backup feature to limit the duration of

the fast charge stage. The fast charge timer is always enabled and

cannot be disabled. See Table 3 in the section Charge Rate

Selection for more information. To limit the total charge time to ten

hours, refer to the section Ten Hour Timer Mode for more

information.

Charge Termination Methods

Charge termination schemes include voltage slope, fast charge

timer and, if desired, a ten hour timer to limit total charge time.

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

ICS1722 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

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