AAT3663_08 Datasheet, PDF (20/23 Pages) Advanced Analogic Technologies – 1A Linear Li-Ion Battery Charger for Single and Dual Cell Applications

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PRODUCT DATASHEET
AAT3663
1A Linear Li-Ion Battery Charger for Single and Dual Cell Applications
By substitution, we can derive the maximum charge cur-
rent before reaching the thermal limit condition which
will activate digital thermal loop operation. The maxi-
mum charge current is the key factor when designing
battery charger applications.
In general, the worst case condition is when the greatest
input to output voltage drop occurs across the charger
IC. Specifically when battery voltage is charged up just
above the preconditioning voltage threshold and the
charger enters into the constant current fast charging
mode. Under this condition, the device will suffer the
maximum possible power dissipation since both the volt-
age difference across the device and the charge current
will be at their respective maximums. Figure 6 shows
the safe fast charge current operating region for differ-
ent ambient temperatures. Exceeding these limits will
drive the charge control into digital thermal loop opera-
tion. When under digital thermal loop operation, the
device will remain active and continue to charge the bat-
tery at a reduced current level for the given ambient
condition.
1000
800
T_A = 85°C T_A = 60°C
600
T_A = 45°C
T_A = 25°C
400
200
0
4
5
6
7
8
9 10 11 12 13
V_IN (V)
Figure 6: Maximum Charging Current Before the
Digital Thermal Loop Becomes Active.
Capacitor Selection
Input Capacitor
In general, it is a good design practice to place a decou-
pling capacitor between the IN pin and ground. 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 lockout threshold during device
enable and when battery charging is initiated. If the
AAT3663’s input is to be used in a system with an exter-
nal power supply source, such as a typical AC-to-DC wall
adapter, then a C_IN capacitor in the range of 10μF should
be 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 AAT3663 only requires a 1μF ceramic capacitor 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
AAT3663 is to be used in applications where the battery
can be removed from the charger, such as desktop
charging cradles, an output capacitor 10μF or greater is
recommended to reduce the effect of the charger cycling
on and off when no battery is present.
Printed Circuit Board
Layout Considerations
For the best results, it is recommended to physically place
the battery pack as close as possible to the AAT3663 BAT
pin. To minimize voltage drops on the PCB, keep the high
current carrying traces adequately wide. For maximum
power dissipation of the AAT3663 3x3mm 14-pin TDFN
package, the metal substrate should be solder bonded to
the board. It is also recommended to maximize the sub-
strate contact to the PCB ground plane layer to further
increase local heat dissipation. Refer to the AAT3663
evaluation board for a good layout example.
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3663.2008.01.1.2