AAT3688AIWP-4.2-4-T1 AnalogicTech, AAT3688AIWP-4.2-4-T1 Datasheet - Page 18

• Manufacturer Part Number: AAT3688AIWP-4.2-4-T1
• Description: USB Port Lithium-Ion/Polymer Battery Charger
• Manufacturer: AnalogicTech

Capacitor Selection
Input Capacitor
In general, it is good design practice to place a decou-
pling capacitor between the V
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 AAT3688 USB input is to be used in a system with
an external power supply source rather than a USB port
V
capacitor 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” in. 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.
18
BatteryManager
BUS
, such as a typical AC-to-DC wall adapter, then a C
TM
USB
pin and ground. An input
w w w . a n a l o g i c t e c h . c o m
USB Port Lithium-Ion/Polymer Battery Charger
IN
Output Capacitor
The AAT3688 only requires a 1μF ceramic capacitor on
the BAT pin to maintain circuit stability.
should be increased to 10μF or more if the battery con-
nection is made any distance from the charger output.
If the AAT3688 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 physically
place the battery pack as close as possible to the
AAT3688 BAT pin. To minimize voltage drops on the PCB,
keep the high current carrying traces adequately wide.
For maximum power dissipation of the AAT3688 3x3mm
TDFN package, the metal substrate should be solder
bonded to the board. It is also recommended to maxi-
mize the substrate contact to the PCB ground plane layer
to further increase local heat dissipation.
AAT3688 evaluation board for a good layout example
(see Figures 5 and 6).
PRODUCT DATASHEET
AAT3688
3688.2007.12.1.6
Refer to the
This value