AAT3693 Advanced Analogic Technologies, Inc., AAT3693 Datasheet - Page 17

• Manufacturer Part Number: AAT3693
• Description: 1.6a Lithium-ion/polymer Battery Charger In 2.2x2.2 Tdfn
• Manufacturer: Advanced Analogic Technologies, Inc.

The thermal loop control re-evaluates the circuit die
temperature every three seconds and adjusts the fast
charge current back up in small steps to the full fast
charge current level or until an equilibrium current is
discovered and maximized for the given ambient tem-
perature condition. The thermal loop controls the sys-
tem charge level; therefore, the AAT3693 will always
provide the highest level of constant current in the fast
charge mode possible for any given ambient tempera-
ture condition
Thermal Considerations
The AAT3693 is offered in the TDFN2.2x2.2-10 package,
which can provide up to 2W of power dissipation when
properly bonded to a printed circuit board and has a
maximum thermal resistance of 50°C/W. Many consid-
erations should be taken into account when designing
the printed circuit board layout, as well as the place-
ment 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 situa-
tion should be calculated:
Where:
P
θ
T
T
Figure 5 shows the relationship between maximum power
dissipation and ambient temperature for the AAT3693.
BatteryManager
3693.2009.04.1.1
A
D(MAX)
JA
J
= Thermal Loop Entering Threshold (°C) (115°C]
= Ambient Temperature (°C)
= Package Thermal Resistance (°C/W)
= Maximum Power Dissipation (W)
P
D(MAX)
TM
=
(T
J
θ
- T
JA
A
)
1.6A Lithium-Ion/Polymer Battery Charger in 2.2x2.2 TDFN
w w w . a n a l o g i c t e c h . c o m
Next, the power dissipation can be calculated by the fol-
lowing equation:
Where:
P
V
V
I
I
By substitution, we can derive the maximum charge cur-
rent before reaching the thermal limit condition (thermal
loop). The maximum charge current is the key factor
when designing battery charger applications.
In general, the worst condition is the greatest voltage
drop across the charger IC, when battery voltage is
charged up to the preconditioning voltage threshold and
before entering thermal loop regulation.
CH
OP
D
IN
BAT
Application
for Normal Operation [0.3mA]
Figure 5: Maximum Power Dissipation Before
= Total Power Dissipation by the Device
= Quiescent Current Consumed by the Charger IC
= Constant Charge Current Programmed for the
= Input Voltage
= Battery Voltage as Seen at the BAT Pin
1.5
0.5
2.5
2
1
0
0
P
I
D
CH(MAX)
I
Entering Thermal Loop.
= [(V
CH(MAX)
IN
=
25
PRODUCT DATASHEET
=
- V
(T
(P
BAT
J(MAX)
D(MAX)
θ
) · I
JA
T
V
V
A
- T
50
IN
IN
AAT3693
(° ° C)
CC
- V
- V
- V
A
+ (V
)
- V
BAT
BAT
IN
· I
IN
IN
OP
· I
75
· I
)
OP
OP
)]
100
17