ICS1712M GALAXY [Galaxy Power, Inc.], ICS1712M Datasheet - Page 13

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

To set the voltage at the THERM pin for 1.67V at 25 C, the
equivalent divider looks like Figure 11.
The parallel resistance R is calculated:
The internal pull-up resistance R
known so the external fixed resistor can be calculated from:
Substituting in known values: R
value is used for R
Since the thermistor resistance R
a particular temperature, the voltage across the thermistor V
that temperature can be calculated from:
with the drop across the resistor divider equal to 5V. For this
example, the calculated voltage with R
and with R
internal thresholds for hot and cold battery detection. If the voltage
across the thermistor (at the THERM pin) drops below 0.93V, the
ICS1712 will shut down due to a hot battery fault condition and
will not restart unless reset. If the voltage dropped across the
thermistor is above 2.4V before fast charge is initiated, the
ICS17012 will begin a reduced current charge. See the Cold
Battery Charging section for more information.
Figure 11: Equivalent voltage divider
th
=4.7k
R
fix
.
V
at 45 C the voltage is 0.95V. Table 3 lists the
= 5V - 1.67V
th
R
= __________ (5V),
fix
1.67V/10k
= __________ .
R
R
R
R
pu
pu
th
pu
th
fix
pu
and the parallel resistance R are
is specified by manufacturers at
(5V)
-
+
= 27.27k . A 27k
R
R
R
th
=20k .
=18k
at 10 C is 2.37V
standard
th
at
13
As a battery approaches full charge, its accelerated rate of heating
can be used to terminate fast charge by detecting the large change
in the temperature slope. The large change in temperature slope is
proportional to the thermistor voltage change per unit of time. If
the DTSEL pin is programmed for temperature slope termination,
the controller will calculate the thermistor voltage slope and
terminate based on internally set thresholds as listed in Table 1.
The threshold is 40mV per minute for selected charge rates greater
than C/2 and 28mV per minute for selected charge rate C/2. The
voltage across the thermistor must change at these rates or greater
to terminate the selected charge rate.
These thresholds correspond to a set change in thermistor
resistance when an external pull-up to 5V is used as shown in
Figure 11. Using the values calculated from the hot and cold
battery detection example, the percent change in the thermistor
resistance per minute for selected charge rates are provided. For
selected charge rates greater than C/2, the thermistor resistance
must decrease 4%/min. to terminate charge. For selected charge
rate C/2, the thermistor resistance must decrease 3%/min. to
terminate charge.
Cold Battery Thermistor
Voltage
Hot Battery Thermistor
Voltage
Using an NTC thermistor for temperature slope
termination:
Table 4: Thermistor Voltage Thresholds
Parameter
Voltage
<0.93
>2.4
ICS1712
Temperature
Battery
<10 C
>45 C