AAT3697IWP-4.2-T1 Advanced Analog Technology, Inc., AAT3697IWP-4.2-T1 Datasheet - Page 17

• Manufacturer Part Number: AAT3697IWP-4.2-T1
• Description: 2A Lithium-Ion/Polymer Battery Charger
• Manufacturer: Advanced Analog Technology, Inc.

Thermal Considerations
The AAT3697 is offered in a 3x3mm TDFN pack-
age which can provide up to 2.0W of power dissi-
pation when it is properly bonded to a printed cir-
cuit 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 effect 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:
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.
3697.2007.02.1.1
CC
OP
D
IN
BAT
Eq. 7:
= Total Power Dissipation by the Device
= Input Voltage Amplitude, V
= Battery Voltage as Seen at the BAT Pin
= Maximum Constant Fast Charge Current
= Quiescent Current Consumed by the
Programmed for the Application
Charger IC for Normal Operation
Eq. 8:
P
D
= [(V
T
IN
A
- V
= T
BAT
J
- (θ
) · I
JA
CC
· P
+ (V
ADP
D
)
IN
· I
OP
)]
2A Lithium-Ion/Polymer Battery Charger
Where:
T
T
P
θ
Example:
For an application where the fast charge current for
the adapter mode is set to 1A, V
battery voltage at 3.6V, what is the maximum ambi-
ent temperature at which the thermal loop will
become active?
Given:
V
V
I
I
T
θ
Using Equation 7, calculate the device power dissi-
pation for the stated condition:
The maximum ambient temperature before the
AAT3697 thermal loop becomes active can now be
calculated using Equation 8:
Therefore, under the stated conditions for this
worst case power dissipation example, the
AAT3697 will enter the thermal loop and lower the
fast charge constant current when the ambient
operating temperature rises above 39.8°C.
CC
OP
Eq. 9:
JA
JA
A
J
J
D
ADP
BAT
= Maximum Device Junction Temperature
= Ambient Temperature in °C
= Total Power Dissipation by the Device
Eq. 10:
= Package Thermal Resistance in °C/W
Below the Thermal Loop Threshold
= 5.0V
= 3.6V
= 1A
= 0.75mA
= 50°C/W
= 110°C
P
D
= (5.0V - 3.6V) (1A) + (5.0V · 0.75mA)
= 1.40375W
T
A
= 110°C - ( 50°C/W · 1.40375W)
= 39.8125°C
ADP
AAT3697
= 5.0V and the
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