6

ICS1708

Battery Detection

If upon initial power-up, voltage at VIN pin 7 is less than 0.5V, the ICS1708 assumes no battery is present, and the polling detect mode is

initiated.

The ICS1708 enters the polling detect mode using CHG pin 1 and applies a 100ms charge pulse. During the first 4ms pulse, the ICS1708

monitors the VIN pin 7 to determine if voltage is above the voltage set on OPREF pin 6. If the battery is present, the voltage at VIN pin 7

will be held below the voltage set on OPREF pin 6 while the current pulse is applied. If a battery is not present, the voltage at VIN pin 7 will

rise above the voltage set on OPREF pin 6.

If the voltage at VIN pin 7 exceeds the voltage set on OPREF pin 6, the ICS1708 will wait for about one-half second after the 100ms charge

pulse ends before producing another 100ms charge pulse. The process repeats until the battery connects. When the battery connects, the

100ms polling pulse is extended for another 100ms and the pulse becomes the first

discharged or low voltage battery does not interfere with a prompt start of

detect mode if the battery is removed.

Battery Removal

During the first 4ms of the application of a charge pulse, the voltage at the VIN pin 7 is compared to the voltage set at the OPREF pin 6. If

the voltage at VIN pin 7 is greater than the voltage set at OPREF pin 6 during the application of the current pulse, then the battery is

assumed to have been removed and the ICS1708 enters the polling detect mode. If the voltage at VIN pin 7 is held below the voltage set at

OPREF pin 6, charging continues.

When in the topping charge or maintenance charge stages, a charge pulse may not occur for several seconds or longer. So, during the period

between charge pulses, the voltage at VIN pin 7 is compared to the internal 0.5V reference. If the voltage at VIN pin 7 is less than 0.5V, the

ICS1708 assumes the battery has been removed, and the polling detect mode is initiated.

Pin Descriptions

In addition to a regulated +5V supply, the ICS1708 requires a few other external components to control the clock rate and provide an

indicator display. The ICS1708 is interfaced to turn on and off an external current source

Output Logic Signals: CHG pin1

The CHG pin 1 is active high/low, TTL compatible output. In addition to being TTL compatible, the CMOS output is capable of sourcing

and sinking up to 25mA which adds flexibility when interfacing to other circuitry. A logic high on CHG pin 1 indicates that the constant

current source is on. A logic low turns off the constant current source. Normal care must be taken to control wiring resistance and

inductance.

Charge Status Indicators: CMN pin 3, MMN pin 2

The controller has to two outputs for driving external indicators. These pins are active low. These two indicator outputs are open drains

when off. They can sink up to 40mA which allows for sinking LED current with use of external current limiting resistors. These two

indicator outputs denote charge status: fast charge or topping/maintenance charging as shown in Table 1.

Table 1: Indicator Description List

MMN

CMN

Description

On

Charge complete (battery ready to use) as maintenance or topping charge is applied

On

Fast charge (including SoftStart conditioning)

Flash

See applications information

On

At power-up or with battery insertion

The charge mode (CMN) indicator is low continuously during the

charge stage, the output turns off and the indicator turns off. When the maintenance mode (MMN) indicator is on and as the battery is ready

to use, the ICS1708 applies the topping and maintenance charge.

The ICS1708 does not control the current flowing into the battery in any way other than turning it on and off. The required current for the

selected charge rate is provided by the system's input power source. The external charging circuitry provides current at the selected charge

rate. For example, to charge a 1.2 ampere hour battery in 60 minutes (1C), 1.2 amperes is required.