AAT3681_08 Datasheet, PDF (13/15 Pages) Advanced Analogic Technologies – USB Port or AC Adapter Lithium-Ion/Polymer Battery Charger

BatteryManager^TM
PRODUCT DATASHEET
AAT3681
USB Port or AC Adapter Lithium-Ion/Polymer Battery Charger
I_CH(MAX) =
(P_D(MAX) - V_IN · I_OP)
V_IN - V_BAT
I_CH(MAX) =
(T_J(MAX) -
θ_JA
T_A)
-
V_IN
·
I_OP
V_IN - V_BAT
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.
Figure 4 shows the maximum charge current in different
ambient temperatures.
300
T_A = 25°C
250
T_A = 45°C
200
150
100 ^TA ^{= 85°C}
T_A = 60°C
50
0
4.25 4.5 4.75 5 5.25 5.5 5.75 6 6.25 6.5 6.75 7
V_IN (V)
Figure 4: Maximum Charging Current Before
Thermal Cycling Becomes Active.
Capacitor Selection
Input Capacitor
In general, it is good design practice to place a decou-
pling 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 lockout threshold during device
enable and when battery charging is initiated. If the
AAT3681 adapter input is to be used in a system with an
external 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 applica-
tion will minimize switching or power transient effects
when the power supply is “hot plugged” in.
Output Capacitor
The AAT3681 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
AAT3681 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.
Printed Circuit Board
Layout Considerations
For the best results, it is recommended to physically
place the battery pack as close as possible to the
AAT3681 BAT pin. To minimize voltage drops on the PCB,
keep the high current carrying traces adequately wide.
Refer to the AAT3681 evaluation board for a good layout
example (see Figures 5 and 6).
3681.2007.12.1.5
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