16

ICS1700A

Charging System Status by Indicator

The Indicator Description List in Table 1 contains displays that are

caused by charging system abnormalities. At power-up or after a

reset is issued, one flash of the CMN indicator followed by a

continuous PFN indication results from a voltage present at the

battery terminals with the current source off and no battery. Check

the current source and ensure that it produces no more than the

equivalent of 350mV/cell when turned off with no battery. If the

VIN divider resistors were not properly selected, an open circuit

voltage that is actually less than the equivalent of 350mV/cell with

the charger off and no battery will not divide down this open

circuit voltage properly and produce a PFN fault indication. Check

the VIN divider and ensure that it properly normalizes the battery

voltage to the electrochemical potential of about 1.2V cell. If the

PFN fault indicator is active immediately after power-up or after a

reset is issued with the battery installed, then the constant current

source is producing more than the equivalent of 350mV/cell when

off and there is an open connection between the charger terminals

and the battery. Check wires, connections, battery terminals, and

the battery itself for an open circuit condition.

If the CMN and OTN indicators are active together, this is an

indication that the battery temperature has dropped to below 10

after a fast charge was initiated with the battery temperature

normal. If this condition is observed and the battery temperature

did not drop after fast charge was initiated, check the thermistor

circuit mechanically for poor contact and electrically for excessive

noise.

Enhanced Performance Characteristics

The ICS1700A is an enhanced performance, pin-for-pin re-

placement for the original ICS1700. Improved internal features

provide additional capabilities. The charge sequence, voltage slope

termination method, and analog-to-digital converter resolution

allow the ICS1700A to charge either NiMH or NiCd batteries. The

ICS1700A accepts either a thermal switch or thermistor input for

temperature sensing. The polling mode for battery detection

responds quickly to the removal of the battery throughout the

charge sequence. The reset input debounce eliminates sensitivity to

field effects and ground bounce when the PC board design

recommendations cited in this document are employed. The

temperature sense input debounce eliminates sensitivity to shock

and vibration associated with the use of a thermal switch.

Maximum Temperature Termination

Maximum temperature termination is best suited as a safety back-

up feature. Maximum temperature termination requires that the

thermal sensor be in intimate contact with the battery. A low

thermal

impedance

contact

area

is

required

for

accurate

temperature sensing. The area and quality of the contact surface

between the sensor and the battery directly affects the accuracy of

temperature sensing. Thermally conductive adhesives may have to

be considered in some applications to ensure good thermal transfer

from the battery case to the sensor.

The thermal sensor should be placed on the largest surface of the

battery for the best accuracy. The size of the battery is also a

consideration when using temperature termination. The larger the

battery, lower the surface area to volume ratio. Because of this,

larger batteries are less capable in dissipating internal heat.

Additional considerations beyond the basics mentioned above may

be involved when using maximum temperature termination where

sudden changes in ambient temperature occur or where forced air

cooling is used. For these applications, the surface area of the

thermal sensor in contact with the battery compared to the surface

area of the thermal sensor in contact with the ambient air may be

significant. For example, bead type thermistors are relatively small

devices which have far less thermal capacity compared to most

batteries. Insulating the surface of the thermistor that is in contact

with the ambient air should help minimize heat loss by the

thermistor and maintain accuracy.