10

ICS1700A

Figure 7:Voltage levels for temperature

sensing with a thermistor or thermal switch

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

current below 10

18k

an internal voltage threshold at 10

voltage at 45

at the THERM pin is set at the midpoint of the thresholds:

0.93V + 2.40V - 0.93V

=1.67V.

2

The THERM pin has a 75k

resistor divider with 10k

Master Reset: MRN Pin

The MRN pin is provided to re-program the controller for a new

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 change charge

rates or clear a temperature fault condition. Upon power-up, the

controller automatically re-sets 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

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 maximum temperature 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 7 shows the internal thresholds over laid on a typical

thermistor curve.

detection:

Figure 8: Voltage divider at the THERM pin

at 25