AAT3681AIJS-4.2-2-T1 ANALOGICTECH [Advanced Analogic Technologies], AAT3681AIJS-4.2-2-T1 Datasheet - Page 13

• Manufacturer Part Number: AAT3681AIJS-4.2-2-T1
• Description: 500mA USB Port or AC Adapter Lithium-Ion/Polymer Battery Charger
• Manufacturer: ANALOGICTECH [Advanced Analogic Technologies]

Figure 3 shows the relationship of maximum power
dissipation and ambient temperature of AAT3681A.
Next, the power dissipation can be calculated by
the following equation:
Where:
P
V
V
I
I
By substitution, we can derive the maximum
charge current before reaching the thermal limit
condition (thermal cycling). The maximum charge
current is the key factor when designing battery
charger applications.
3681A.2007.10.1.2
CH
OP
D
IN
BAT
Figure 3: Maximum Power Dissipation.
= Total Power Dissipation by the Device
= Input Voltage
= Battery Voltage as Seen at the BAT Pin
= Constant Charge Current Programmed for
= Quiescent Current Consumed by the
1000
800
600
400
200
the Application
Charger IC for Normal Operation [0.5mA]
0
0
P
I
CH(MAX)
D
I
= [(V
CH(MAX)
20
=
IN
=
- V
(T
(P
BAT
J(MAX)
40
D(MAX)
θ
) · I
JA
V
T
V
A
- T
IN
CH
IN
(° ° C)
- V
- V
A
- V
+ (V
)
60
- V
BAT
IN
BAT
· I
IN
IN
OP
· I
· I
)
OP
80
OP
)]
100
Lithium-Ion/Polymer Battery Charger
In general, the worst condition is the greatest volt-
age drop across the charger IC, when battery volt-
age is charged up to the preconditioning voltage
threshold. Figure 4 shows the maximum charge
current in different ambient temperatures without
PCB thermal enhancements.
Capacitor Selection
Input Capacitor
In general, it is good design practice to place a
decoupling capacitor between the ADP pin and
GND. An input capacitor in the range of 1µF to 22µF
is recommended. If the source supply is unregulated,
it may be necessary to increase the capacitance to
keep the input voltage above the under-voltage lock-
out threshold during device enable and when battery
charging is initiated. If the AAT3681A adapter input is
to be used in a system with an external power sup-
ply source, such as a typical AC-to-DC wall adapter,
then a C
used. A larger input capacitor in this application will
minimize switching or power transient effects when
the power supply is "hot plugged" in.
Output Capacitor
The AAT3681A only requires a 1µF ceramic capac-
itor on the BAT pin to maintain circuit stability. This
value should be increased to 10µF or more if the
battery connection is made any distance from the
charger output. If the AAT3681A is to be used in
applications where the battery can be removed
from the charger, such as with desktop charging
cradles, an output capacitor greater than 10µF may
be required to prevent the device from cycling on
and off when no battery is present.
Figure 4: Maximum Charging Current Before
500mA USB Port or AC Adapter
500
450
400
350
300
250
200
150
100
50
4.25
0
Thermal Cycling Becomes Active.
T
IN
A
4.5
= 85°C
capacitor in the range of 10µF should be
4.75
T
5
A
= 60°C
5.25
T
A
= 25°C
5.5
V
IN
T
5.75
(V)
A
= 45°C
AAT3681A
6
6.25
6.5
6.75
7
13