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ICS1708

Charge Termination Methods

Charge termination methods include voltage slope and fast charge time out.

Voltage Slope Termination

The most distinctive point on the voltage curve of a battery in response to charging by a constant amplitude current is the voltage peak that

occurs as the battery 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 peak

voltage. Using milestone voltage slope data as charging progresses, the ICS1708 determines when the point of full charge will occur and

accurately terminates the applied current when the battery reaches that point. The actual termination point is based on the actual charging

characteristics of the particular battery. Typically, fast charge ends around peak voltage.

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

New, over-discharged, old, and already full batteries often produce a voltage profile that varies from that shown in Figure 6. The ICS1708

fast charge termination in these cases is based on a slight decrease in the voltage. Some new batteries may need several charge/use cycles

before their response fully stabilizes to that shown in Figure 6.

Charge Timer Termination

The controller uses a timer to limit fast charge duration. These times are internally set according to the charge rate selected and can be

adjusted slightly by changing the clock frequency. Fast charge timer termination is a safety backup feature to limit the duration of the fast

charge stage. The fast charge timer is always active and cannot be disabled. See Table 3 Charge Rate List.