ICS1700A Datasheet, PDF (6/24 Pages) List of Unclassifed Manufacturers – QuickSaver Charge Controller for Nickel-Cadmium and Nickel-Metal Hydride Batteries

ICS1700A
Charge Termination Methods
Several charge termination schemes, including voltage slope,
maximum temperature and a fast charge timer are available. The
voltage slope method may be used with or without 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
ICS1700A 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.
Cells that are not thoroughly conditioned or possess an unusual cell
construction may not have a normal voltage profile. The
ICS1700A 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.
Maximum Temperature Termination
Maximum temperature can be sensed using either a NTC
thermistoror a thermal switch. Maximum temperature termination
can also be bypassed if desired, although it is strongly
recommended that some form of temperature termination be used.
If an NTC thermistor is used, an internal voltage threshold
Determines when the battery is too hot to charge. As temperature
increases, the voltage across the thermistor will drop. This voltage
is continually compared to the internal voltage thresh-old. If the
thermistor voltage drops below the internal thresh-old, the OTN
indicator is activated and the controller shuts down. The controller
must be reset once the hot battery fault condition has cleared to
restart the charge sequence.
If a thermal switch is used, a 45°C open circuit switch is
recommended. When the thermal switch opens, an internal pull-up
at the THERM pin results in a logic high which shuts down the
controller and activates the OTN indicator. The controller must be
reset once the hot battery fault condition has cleared to restart the
charge sequence.
Maximum temperature termination can be disabled by grounding
the THERM pin. See the section on Temperature Sensing for more
information.
Fast 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 best suited as 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 2 for more information.
Figure 6: Voltage and slope curves showing inflection and zero slope points
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