ICS1708 Datasheet, PDF (7/16 Pages) List of Unclassifed Manufacturers – QuickSaver Charge Control IC for Nickel-Cadmium and Nickel-Metal Hydride Batteries

ICS1708
Clock Input: RC Pin
The RC pin is used to set the frequency of the internal clock. Alternatively, an external 1 MHz clock may be used. Normally an external
resistor is connected between this pin and VDD. An external capacitor is connected between this pin and ground (VSS). The frequency of
the internal clock is typically 1 MHz with a 15kΩ resistor and a 100pF capacitor. All time durations noted in this document are based on a 1
MHz clock. Operating the clock at a lower frequency will proportionally change all time durations. Operating the clock at a frequency
significantly lower than 1 MHz, without adjusting the charge current accordingly, will lessen the effectiveness of the fast charge timer and
lower the accuracy of the controller. Operating the clock at a frequency greater than 1 MHz will also change all time durations and, without
adjusting the charge current accordingly, may cause termination to occur due to the fast charge timer expiring rather than by the battery
reaching full charge.
The clock may be driven by a 1 MHz external 0 to 5V pulse provided the duty cycle is between 10% and 60%. The clock input impedance is
typically 1kΩ.
Voltage Input: VIN Pin
The battery voltage is normalized by an external resistor divider network to one cell. The electrochemical potential of one cell is about 1.2V.
For example, if the battery consists of six cells in series, the voltage at the VIN pin should be set to equal to the total battery voltage divided
by six. This is accomplished with two resistors, as shown in Figure 7.
VIN pin
# of cells
R1
R2
Figure 7: Resistor divider network at the VIN pin
To determine resistor values, count the number of cells to be charged in series. Then choose either R1 or R2 and solve for the other resistor
using:
R1 = R2 * (# of cells -1) or R2 =
R1 ___
(# of cells -1)
R2 value should be kept below 27K so that if a 0.047µF capacitor is used in parallel with it, more than five RC time constants
occur before data acquisition. Consult the factory for applications that require use of higher resistance voltage dividers.
Circuit Voltage Reference: OPREF pin 6
The OPREF pin has an internal 85kΩ pull-up resistor to VDD. OPREF requires an external pull-down resistor to establish the open circuit
(no battery) voltage reference. The purpose of this voltage reference is to detect the removal of the battery from the charging system. The
voltage at this pin is compared to the voltage at the VIN pin for the first 4mssec after the current source is turned on by CHG pin 1. If the
voltage at VIN is greater than the voltage set on OPREF, the ICS1708 assumes the battery has been removed and the ICS1708 enters the
polling detect mode.
For proper operation, the voltage on OPREF pin 6 is set below the (divided down) no battery voltage at VIN pin 7 produced by the current
source (when on) and above the maximum normalized voltage at VIN pin 7 with a battery present. The OPREF pin voltage must not exceed
2.3V or it will prevent the start of fast charge. If the voltage on OPREF exceeds 4V, the controller will shutdown and power to the ICS1708
must be removed and restored to restart the ICS1708.
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