AAT3685 AAT, AAT3685 Datasheet - Page 18

• Manufacturer Part Number: AAT3685
• Description: Lithium-Ion/Polymer Battery Charger
• Manufacturer: AAT

Data Timing
The system microcontroller should assert an active
low data request pulse for minimum duration of
200ns; this is specified by T
the rising edge of the end of the data request pulse,
Timing Diagram
Thermal Considerations
The AAT3685 is packaged in a Pb-free, 3x3mm
TDFN package which can provide up to 2.0W of
power dissipation when it is properly bonded to a
printed circuit board and has a maximum thermal
resistance of 50°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 gen-
erating devices in a given application design. The
ambient temperature around the charger IC will
also have an affect on the thermal limits of a bat-
tery 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:
18
Eq. 4:
SQ
CK
Data
P
D
= [(V
T
T
DATA(RPT)
OFF
IN
> 2 P
- V
BAT
= T
DATA
T
System Start
SQ
System Reset
SYNC
) · I
SYNC
LO(DATA)
PULSE
CC
+ T
+ (V
LAT
. Upon sensing
< 2.5 P
IN
T
LAT
· I
OP
DATA
)]
P
DATA
Lithium-Ion/Polymer Battery Charger
N=1
the AAT3685 status data control will reply the data
word back to the system microcontroller after a
delay specified by the data report time specification
T
pulses will be specified by the T
Where:
P
V
V
I
I
Next, the maximum operating ambient temperature
for a given application can be estimated based on
the thermal resistance of the 3x3mm TDFN pack-
age when sufficiently mounted to a PCB layout and
the internal thermal loop temperature threshold.
CC
OP
DATA(RPT)
D
IN
BAT
= Total Power Dissipation by the Device
= Input Voltage Level, V
= Battery Voltage as Seen at the BAT Pin
= Maximum Constant Fast Charge Current
= Quiescent Current Consumed by the
N=2
Programmed for the Application
Charger IC for Normal Operation
. The period of the following group of data
Eq. 5: T
N=3
A
= T
T
OFF
J
- (θ
ADP/USB
JA
DATA
· P
AAT3685
D
)
specification.
3685.2006.10.1.3