AAT3685IWP-4.2-T1 Analogic Tech, AAT3685IWP-4.2-T1 Datasheet - Page 18

• Manufacturer Part Number: AAT3685IWP-4.2-T1
• Description: Battery Management Lithium-Ion/Polymer Battery Charger
• Manufacturer: Analogic Tech

Specifications of AAT3685IWP-4.2-T1

• Package / Case: TDFN33-12
• Mounting Style: SMD/SMT
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

The maximum ambient temperature before the AAT3685
thermal limit protection will shut down charging can now
be calculated using Equation 5:
Therefore, under the stated conditions for this worst
case power dissipation example, the AAT3685 will sus-
pend charging operations when the ambient operating
temperature rises above 89.81°C.
Capacitor Selection
Input Capacitor
In general, it is good design practice to place a decou-
pling capacitor between the ADP/USB pin and ground. An
input capacitor in the range of 1μF to 22μF is recom-
mended. 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 AAT3685 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
18
BatteryManager
BUS
, such as a typical AC-to-DC wall adapter, then a C
Eq. 7:
T
A
= 89.81°C
= 140°C - ( 50°C/W · 1.00375W)
TM
w w w . a n a l o g i c t e c h . c o m
IN
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.
Output Capacitor
The AAT3685 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 AAT3685 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
AAT3685 BAT pin. To minimize voltage drops on the PCB,
keep the high current carrying traces adequately wide.
For maximum power dissipation of the AAT3685 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.
AAT3685 evaluation board for a good layout example
(see Figures 5 and 6).
Lithium-Ion/Polymer Battery Charger
PRODUCT DATASHEET
AAT3685
3685.2007.12.1.4
Refer to the
This value