AAT3690IWP-4.2-T1 Advanced Analog Technology, Inc., AAT3690IWP-4.2-T1 Datasheet - Page 17

• Manufacturer Part Number: AAT3690IWP-4.2-T1
• Description: 1.0A USB Port/Adapter Lithium-Ion/Polymer Battery Charger
• Manufacturer: Advanced Analog Technology, Inc.

Capacitor Selection
Input Capacitor
In general, it is good design practice to place a
decoupling capacitor between the ADP and USB
pins 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 AAT3690 adapter input is to be used in a sys-
tem with an external power supply source, such as
a typical AC-to-DC wall adapter, then a C
tor in the range of 10μF should be used. A larger
input capacitor in this application will minimize
switching or power bounce effects when the power
supply is "hot plugged." Likewise, a 10μF or greater
input capacitor is recommended for the USB input
to help buffer the effects of USB source power
switching, noise, and input cable impedance.
3690.2007.01.1.2
USB
ADP
BAT
C1
10μF
Figure 3: AAT3690 Evaluation Board Schematic.
C2
10μF
BAV74LT1
BAV74LT1
DS1 (b)
DS1 (a)
C3
10μF
TS
IN
10K
R3
capaci-
J1
CT
ON/OFF
1 2 3
Lithium-Ion/Polymer Battery Charger
C4
0.1μF
5
1
3
2
6
9
Output Capacitor
The AAT3690 only requires a 1μF ceramic capaci-
tor 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 AAT3690 is to be used in
applications where the battery can be removed
from the charger, such as in the case of 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 physical-
ly place the battery pack as close to the AAT3690
BAT pin as possible. To minimize voltage drops on
the PCB, keep the high current carrying traces ade-
quately wide. For maximum power dissipation of
the AAT3690 TDFN package, the metal substrate
should be solder bonded to the board. It is also rec-
ommended to maximize the substrate contact to the
PCB ground plane layer to further increase local
heat dissipation.
U1
AAT3690
EN
USB
ADP
BAT
TS
CT
USBSET
ADPSET
STAT2
STAT1
GND
USB
1.0A USB Port/Adapter
10
7
8
11
12
4
J2
0
GRN
LED
R1
8.06K
D2
R5
1.5K
R2
8.06K
RED
LED
D1
R4
1.5K
17