LTC1732-8.4 データシートの表示（PDF） - Linear Technology

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LTC1732-8.4

Lithium-Ion Linear Battery Charger Controller

Linear Technology 

LTC1732-8.4

APPLICATIONS INFORMATION

Constant-Current Only Mode

The LTC1732-8.4 can be used as a programmable current

source by connecting the TIMER pin to VCC. This is

particularly useful for charging NiMH or NiCd batteries. In

the constant-current only mode, the timer and voltage

amplifier are both disabled. An external termination method

is required to properly terminate the charge.

Battery Detection

The LTC1732-8.4 can detect the insertion of a new battery.

When a battery with voltage of less than 8.05V is inserted,

the LTC1732-8.4 resets the timer and a new charge cycle

begins. If the voltage of the new battery is above 8.05V, the

charging will not start if the TIMER has already timed out.

If a new battery (with a voltage above 8.05V) is inserted

while in the charging process, the timer will not be reset

and charging will continue until the timer runs out.

After a time out has occurred and the battery remains

connected, a new charge cycle will begin if the battery

voltage drops below 8.05V due to self-discharge or exter-

nal loading.

VCC Bypass Capacitor

Many types of capacitors can be used for input bypassing.

However, caution must be exercised when using multi-

layer ceramic capacitors. Because of the self resonant and

high Q characteristics of some types of ceramic capaci-

tors, high voltage transients can be generated under some

start-up conditions, such as connecting the charger input

to a hot power source. To minimize these transients, only

ceramic capacitors with X5R or X7R dielectric are recom-

mended. Also, adding 1Ω or 2Ω in series with the ceramic

capacitor will further reduce these start-up transients. For

more information refer to Application Note 88.

Stability

The charger is stable without any compensation when a

P-channel MOSFET is used as the pass transistor.

However, a 10µF capacitor is recommended at the BAT

pin to keep the ripple voltage low when the battery is

disconnected.

If a PNP transistor is used for the pass transistor, a 1000pF

capacitor is required from the DRV pin to VCC. This

capacitor is needed to help stablize the voltage loop. A

10µF capacitor at the BAT pin is also recommended when

a battery is not present.

17328f

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