ICS1708 Datasheet, PDF (4/16 Pages) List of Unclassifed Manufacturers – QuickSaver Charge Control IC for Nickel-Cadmium and Nickel-Metal Hydride Batteries

ICS1708
Fast Charge
In the second stage, the ICS1708 applies the charging current in a repetitive sequence consisting of positive current charging pulses followed
by a rest time and voltage acquisition time. The cycle, shown with charge, rest, and data acquisition periods in Figure 4, repeats every 1.1
seconds until the battery is fully charged.
fast charge pulse width
cycle time
rest time
voltage
acquisition time
Figure 4: Charge cycle showing fast charge current pulses
The amplitude of the current pulse is determined by system parameters such as the current capability of the charging system, the desired
recharge time, battery capacity and the ability of the battery to accept the charge current in the charging environment. The ICS1708 can be
set for three (3) user-selectable fast charge rates: 15 minutes (4C), 60 minutes (1C), or 150 minutes (C/2.5). The CMN indicator is a
continuous active low during this stage. The charge rate is determined by the voltage level on the CMN indicator when the ICS1708 is first
powered-up.
A voltage acquisition window immediately follows a brief rest time after the charge pulse. No charge is applied during the rest time or
during the acquisition window to allow the battery chemistry to settle. Since no current is flowing, the measured cell voltage is not obscured
by any internal or external IR drops or noise. The ICS1708 takes samples of battery voltage during the acquisition window. The voltage
samples are averaged for comparisons to previous and subsequent averages. This method provides a most accurate representation of the true
state of charge of the battery.
Topping Charge
The third stage is a topping charge that applies current at a rate low enough to prevent cell heating but high enough to equalize cells in a
multiple cell packs. The topping stage is not required before putting the battery into immediate service after fast charge completes.
The topping charge is applied for a minimum of two (2) hours. The current consists of the same pulse technique used during the fast charge
stage; however, the delay time is extended as shown in Figure 5. Extending the delay time between charge pulses allows the same charging
current used as in the fast charge stage so that no changes to the current source are necessary. For example, the same charge pulse that
occurs every second at a 1C (1 hour) fast charge rate will occur every eleven (11) seconds for a topping charge rate of C/11. The MMN
indicator is a continuous active low during the topping and maintenance charge stages.
cycle
time
delay time
cycle
time
Figure 5: Representative timing diagram for topping and maintenance charge
Maintenance Charge
The maintenance charge is intended to offset the natural self-discharge of NiCd or NiMH batteries by keeping their cells primed at peak
charge. After the topping charge ends, the ICS1708 begins this charge stage by once again extending the delay time between charge pulses.
The maintenance charge will last for as long as the divided down battery voltage is greater than 0.5V at VIN pin 7. The MMN indicator is a
continuous active low during this stage.
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