ICS1700AM Galaxy Power, Inc., ICS1700AM Datasheet - Page 11

• Manufacturer Part Number: ICS1700AM
• Description: 20 Pin Quicksaver Full-featured Charge Controller For Ni-cd & Ni-mh Batteries.
• Manufacturer: Galaxy Power, Inc.

To set the voltage at the THERM pin for 1.67V at 25 C, the
equivalent divider looks like Figure 9.
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
ICS1700A 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
ICS1700A will begin a reduced current charge. See the Cold
Battery Charging section for more information.
Figure 9: Equivalent voltage divider
th
=4.7k
R
fix
V
.
at 45 C the voltage is 0.95V. Table 3 lists the
th
= 5V - 1.67V
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
11
Table 4: Thermal Switch Voltage Thresholds
A thermal switch that opens at about 45 C is recommended. The
thermal switch must be connected between the THERM pin and
ground. When the thermal switch is closed, the voltage at the
THERM pin must be below 0.5V for normal operation. When the
thermal switch opens (see Figure 10), the internal pull-up at the
THERM pin will raise the voltage above 4.2V and the ICS1700A
will shut down and will not restart unless reset. Table 4 contains
the internal voltage thresholds used with a thermal switch.
Using a thermal switch for hot battery detection:
Cold Battery Thermistor
Voltage
Hot Battery Thermistor
Voltage
Open Thermal Switch
Voltage
Closed Thermal Switch
Voltage
Figure 10: Thermal switch to connection to
Table 3: Thermistor Voltage Thresholds
THERM pin
V
DD
Parameter
R = 75k
Parameter
pu
ground at the THERM pin
normally closed thermal switch
opens at 45ºC
Voltage
Voltage
<0.93
>2.4
>4.2
<0.5
ICS1700A
Temperature
Temperature
Battery
Battery
<10 C
>45 C
>45 C
<45 C