11

ICS1700A

To set the voltage at the THERM pin for 1.67V at 25

equivalent divider looks like Figure 9.

Table 3: Thermistor Voltage Thresholds

A thermal switch that opens at about 45

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.

Figure 9: Equivalent voltage divider

The parallel resistance R

R

=20k

Ω.

1.67V/10k

Ω

The internal pull-up resistance R

pu

and the parallel 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 10: Thermal switch to connection to

ground at the THERM pin

Table 4: Thermal Switch Voltage Thresholds

THERM pin

R = 75k

normally closed thermal switch

opens at 45ºC

V

DD

pu

Parameter

Voltage

Battery

Temperature

Cold Battery Thermistor

Voltage

>2.4

<10

°C

Hot Battery Thermistor

Voltage

<0.93

>45

°C

Parameter

Voltage

Battery

Temperature

Open Thermal Switch

Voltage

>4.2

>45

°C

Closed Thermal Switch

Voltage

<0.5

<45

°C