LTC4065L datasheet(14/16 Pages) LINER

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LTC4065L/LTC4065LX

4065lxfa

Example: Consider an LTC4065L operating from a 5.5V

wall adapter providing 250mA to a 3V Li-Ion battery. The

ambient temperature above which the LTC4065L will

begin to reduce the 250mA charge current is approxi-

mately:

TA = 115°C – (5.5V – 3V) • (250mA) • 60°C/W

TA = 115°C – 0.625W • 60°C/W = 115°C – 37.5°C

TA = 77.5°C

Charging at such high ambient temperatures is not recom-

mended by battery manufacturers.

Furthermore, the voltage at the PROG pin will change

proportionally with the charge current as discussed in the

Programming Charge Current section.

It is important to remember that LTC4065L applications

do not need to be designed for worst-case thermal condi-

tions since the IC will automatically reduce power dissipa-

tion when the junction temperature reaches approximately

115

°C.

Board Layout Considerations

In order to deliver maximum charge current under all

conditions, it is critical that the exposed metal pad on the

backside of the LTC4065L package is soldered to the PC

board ground. Correctly soldered to a 2500mm2 double-

sided 1 oz. copper board the LTC4065L has a thermal

resistance of approximately 60

°C/W. Failure to make

thermal contact between the Exposed Pad on the backside

of the package and the copper board will result in thermal

resistances far greater than 60

°C/W.

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 live power source. For more information, refer to

Application Note 88.

APPLICATIO S I FOR ATIO

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