Datasheet

LTC4065L/
LTC4065LX/LTC4065L-4.1
15
4065lfb
APPLICATIONS INFORMATION
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 approximately:
T
A
= 115°C – (5.5V – 3V) • (250mA) • 60°C/W
T
A
= 115°C – 0.625W • 60°C/W = 115°C – 37.5°C
T
A
= 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
conditions since the IC will automatically reduce power
dissipation when the junction temperature reaches ap-
proximately 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 2500mm
2
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.
V
CC
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 capacitors, 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.