ltc4065edc-4.4 Linear Technology Corporation, ltc4065edc-4.4 Datasheet - Page 14

• Manufacturer Part Number: ltc4065edc-4.4
• Description: Standalone 750ma Li-ion Battery Charger In 2 ? 2 Dfn
• Manufacturer: Linear Technology Corporation

APPLICATIO S I FOR ATIO
LTC4065-4.4
14
Example: Consider an LTC4065-4.4 operating from a 5V
wall adapter providing 750mA to a 3.6V Li-Ion battery. The
ambient temperature above which the LTC4065-4.4 will
begin to reduce the 750mA charge current is approxi-
mately:
The LTC4065-4.4 can be used above 70°C, but the charge
current will be reduced from 750mA. The approximate
current at a given ambient temperature can be calculated:
Using the previous example with an ambient temperature
of 73°C, the charge current will be reduced to approxi-
mately:
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 LTC4065-4.4 applica-
tions do not need to be designed for worst-case thermal
T
T
T
I
I
BAT
BAT
A
A
A
= 115°C – (5V – 3.6V) • (750mA) • 60°C/W
= 115°C – 1.05W • 60°C/W = 115°C – 63°C
= 52°C
=
=
(
(
5
V
V
CC
115
115
– .
–
3 6
V
°
°
BAT
C T
U
C
V
–
–
)
)
73
•
• θ
A
60
U
°
JA
C
°
C W
/
=
W
84
42
°
C A
°
C
/
=
500
U
mA
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 LTC4065-4.4 package is soldered to the PC
board ground. Correctly soldered to a 2500mm
sided 1 oz. copper board the LTC4065-4.4 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. As an example, a
correctly soldered LTC4065-4.4 can deliver over 750mA
to a battery from a 5V supply at room temperature.
Without a backside thermal connection, this number could
drop to less than 500mA.
V
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.
CC
Bypass Capacitor
2
double-
406544f