July 2004

9

M9999-072004

MIC79110

Micrel

capacity. An increase in the charge current during stage 1

does not shorten the total charge time. It will only shorten the

time for stage 1 to complete and lengthen the time in stage 2.

The lithium-ion loses charge due to aging whether it is used

or not. Do not store the batteries at full charge and high heat

because it will accelerate the aging process. Try and store

with 40% charge and in a cool environment.

Lithium-Ion Safety Precautions

Every lithium ion battery pack should have a safety board

which monitors the charge and discharge of the pack and

prevents dangerous occurrences. The specifications of these

safety boards are dictated by the cell manufacturer and may

include the following:

• Reverse polarity protection

• Charge temperature must not be charged when

temperature is lower than 0°C or above 45°C.

0

Start Charging

Lithium-Ion

Battery

Shutdown

Pin

Deoc Flag is Low

Continue Charge

Charging

Monitor Ibat

Deoc Flag is High

Stop Charge

Battery

Charging

Stop Charge

End of Charge

Ibat

Stop Charge

Current Limit

Ieoc<Ibat<Irset

Standby Mode

Do not charge

<Ieoc

Battery Voltage

Die

Temperature

Irset

<Ieoc

1

>4.3V

>125C

<125C

<4.3V

• Charge current must not be too high, typically

below 0.7C

• Discharge current protection to prevent damage

due to short circuits.

• Protection circuitry for over voltage applied to the

battery terminals.

• Overcharge protection circuitry to stop charge

when the voltage per cell rises above 4.3V.

• Over discharge protection circuitry to stop dis-

charge when the battery voltage falls below 2.3V

(varies with manufacturer).

• Thermal shutdown protection for the battery if the

ambient temperature is above 100°C.