AAT3686 AAT, AAT3686 Datasheet - Page 19

• Manufacturer Part Number: AAT3686
• Description: USB Port/AC Adapter Lithium-Ion/Polymer Battery Charger
• Manufacturer: AAT

Thermal Considerations
The AAT3686 is offered in a 3x4mm TDFN pack-
age and a 4x4mm TDFN package, each of which
can provide up to 2.7W of power dissipation when
it is properly bonded to a printed circuit board and
has a maximum thermal resistance of 37°C/W.
Many considerations should be taken into account
when designing the printed circuit board layout, as
well as the placement of the charger IC package in
proximity to other heat generating devices in a
given application design. The ambient temperature
around the charger IC will also have an effect on
the thermal limits of a battery charging application.
The maximum limits that can be expected for a
given ambient condition can be estimated by the
following discussion:
First, the maximum power dissipation for a given
situation should be calculated:
Where:
P
V
Timing Diagram
3686.2006.10.1.9
D
IN
Eq. 1:
= Total power dissipation by the device
= Either V
SQ
CK
Data
mode is selected
P
D
= [(V
ADP
T
T
DATA(RPT)
OFF
IN
or V
> 2 P
- V
BAT
= T
USB
DATA
T
System Start
System Reset
SQ
SYNC
) · I
SYNC
, depending on which
PULSE
CC
+ T
+ (V
LAT
< 2.5 P
IN
T
LAT
· I
OP
DATA
)]
P
DATA
Lithium-Ion/Polymer Battery Charger
N=1
V
I
I
Next, the maximum operating ambient temperature
for a given application can be estimated based on
the thermal resistance of the 3x4mm and 4x4mm
TDFN packages when sufficiently mounted to a
PCB layout and the internal thermal loop tempera-
ture threshold.
Where:
T
T
P
θ
CC
OP
JA
A
J
BAT
D
= Battery voltage as seen at the BAT pin
= Maximum constant fast charge current pro-
= Quiescent current consumed by the charg-
= Ambient temperature in degrees C
= Maximum device junction temperature
= Total power dissipation by the device
= Package thermal resistance in °C/W
N=2
grammed for the application
er IC for normal operation
below the thermal loop threshold
Eq. 2:
N=3
USB Port/AC Adapter
T
A
T
= T
OFF
J
- (θ
JA
· P
D
)
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