ICS1712M GALAXY [Galaxy Power, Inc.], ICS1712M Datasheet - Page 12

• Manufacturer Part Number: ICS1712M
• Description: Charge Controller for Nickel-Cadmium and Nickel-Metal Hydride Batteries
• Manufacturer: GALAXY [Galaxy Power, Inc.]

ICS1712
Master Reset: MRN Pin
The MRN pin is provided to re-program the controller for a new
mode or charging sequence. This pin has an internal pull-up of
about 75k . A logic low on the MRN pin must be present for more
than 700ms for a reset to occur. As long as the pin is low, the
controller is held in a reset condition. A master reset is required to
clear a temperature fault condition, clear the charging system test,
reset the ten hour timer or change charge rates or auxiliary modes.
Upon power-up, the controller automatically resets itself.
Clock Input: RC Pin
The RC pin is used to set the frequency of the internal clock when
an external 1 MHz clock is not available. An external resistor must
be connected between this pin and V
must be connected between this pin and ground. The frequency of
the internal clock will be about 1 MHz with a 16k
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 about 1k .
Temperature Sensing: THERM Pin
The THERM pin is provided for hot and cold battery detection and
for temperature slope termination of fast charge when used in
conjunction with an NTC thermistor. The THERM pin also
provides for hot battery and maximum temperature termination
when used in conjunction with a normally closed thermal switch.
Several internal voltage thresholds are used by the controller
depending on whether a thermistor or a thermal switch is used.
Figure 9 shows the internal thresholds over laid on a typical
thermistor curve.
DD
. An external capacitor
resistor and a
12
The THERM pin requires some thought if a thermistor is going to
be used for hot and cold battery detection. The example below
works for a typical 10k
the controller to prevent charging above 45 C and reducing the
current below 10 C. At 10 C the resistance of the thermistor is
18k . At 45 C, the resistance drops to 4.7k . The ICS1712 has
an internal voltage threshold at 10 C at 2.4V, and an internal
voltage at 45 C at 0.93V as shown in Figure 9. At 25 C the voltage
at the THERM pin is set at the midpoint of the thresholds:
The THERM pin has a 75k
resistor divider with 10k
fixed resistor (R
Figure 10: Voltage divider at the THERM pin
sensing with a thermistor or thermal switch
Using an NTC thermistor for hot and cold battery
detection:
Figure 9:Voltage levels for temperature
0.93V + 2.40V - 0.93V
fix
), the divider looks like Figure 8 at 25 C:
@ 25 C NTC thermistor. Consider using
for the thermistor (R
at 25 C
2
internal pull-up (R
=1.67V.
th
) and a external
pu
). Using a