ICS1700A Datasheet, PDF (11/24 Pages) List of Unclassifed Manufacturers – QuickSaver Charge Controller for Nickel-Cadmium and Nickel-Metal Hydride Batteries

ICS1700A
To set the voltage at the THERM pin for 1.67V at 25°C, the
equivalent divider looks like Figure 9.
Table 3: Thermistor Voltage Thresholds
Parameter
Cold Battery Thermistor
Voltage
Hot Battery Thermistor
Voltage
Voltage
>2.4
<0.93
Battery
Temperature
<10°C
>45°C
Figure 9: Equivalent voltage divider
The parallel resistance R|| is calculated:
R|| = 5V - 1.67V =20kΩ.
1.67V/10kΩ
The internal pull-up resistance Rpu and the parallel resistance R|| are
known so the external fixed resistor can be calculated from:
R_pu R||
R_fix = __________ .
R_pu - R||
Substituting in known values: R_fix = 27.27kΩ. A 27kΩ standard
value is used for R_fix.
Since the thermistor resistance R_th is specified by manufacturers at
a particular temperature, the voltage across the thermistor V_th at
that temperature can be calculated from:
R_th (5V)
V_th = __________ (5V),
R_pu + R||
with the drop across the resistor divider equal to 5V. For this
example, the calculated voltage with R_th=18kΩ at 10°C is 2.37V
and with R_th =4.7kΩ at 45°C the voltage is 0.95V. Table 3 lists the
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.
•Using a thermal switch for hot battery detection:
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.
V_DD
R_pu = 75k
THERM pin
normally closed thermal switch
opens at 45ºC
Figure 10: Thermal switch to connection to
ground at the THERM pin
Table 4: Thermal Switch Voltage Thresholds
Parameter
Open Thermal Switch
Voltage
Closed Thermal Switch
Voltage
Voltage
>4.2
<0.5
Battery
Temperature
>45°C
<45°C
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