AAT3783_12 Datasheet, PDF (17/20 Pages) Skyworks Solutions Inc. – 1-A Linear Li-Ion/Polymer Battery Charger with 28V Over-Voltage Protection

DATA SHEET
AAT3783
1-A Linear Li-Ion/Polymer Battery Charger with 28V Over-Voltage Protection
Where:
P_D = Total Power Dissipation by the Device
V_IN = Input Voltage
V_BAT = Battery Voltage as Seen at the BAT Pin
I_CH = Constant Charge Current Programmed for the
Application
I_OP = Quiescent Current Consumed by the Charger IC
for Normal Operation [0.4mA]
By substitution, we can derive the maximum charge cur-
rent before reaching the thermal limit condition (thermal
loop). The maximum charge current is the key factor
when designing battery charger applications.
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 and
before entering thermal loop regulation. Figure 4 shows
the maximum charge current in different ambient tem-
peratures.
1000
T_A = 45°C
800
T_A = 25°C
600
400
200
T_A = 60°C T_A = 85°C
0
4
4.5
5
5.5
6
6.5
7
7.5
V_IN (V)
Figure 4: Maximum Charging Current Before the
Digital Thermal Loop Becomes Active.
Input Capacitor
A 1μF or larger capacitor is typically recommended for
C_IN. C_IN should be located as close to the device VIN pin
as practically possible. Ceramic, tantalum, or aluminum
electrolytic capacitors may be selected for C_IN. There is
no specific capacitor equivalent series resistance (ESR)
requirement for C_IN. However, for higher current opera-
tion, ceramic capacitors are recommended for C_IN due to
their inherent capability over tantalum capacitors to
withstand input current surges from low impedance
sources such as batteries in portable devices.
Typically, 50V rated capacitors are required for most of
the application to prevent any surge voltage. Ceramic
capacitors selected as small as 1210 are available which
can meet these requirements. Other voltage rating
capacitor can also be used for the known input voltage
application.
Charger Input Capacitor
A 2.2μF decoupling capacitor is recommended to be
placed between INCHR and GND.
Charger Output Capacitor
The AAT3783 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
AAT3783 is used in applications where the battery can be
removed from the charger, such as with desktop charg-
ing 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 Recommendations
For proper thermal management and to take advantage
of the low R_DS(ON) of the AAT3783, a few circuit board
layout rules should be followed: VIN and VOUT should be
routed using wider than normal traces, and GND should
be connected to a ground plane. To maximize package
thermal dissipation and power handling capacity of the
AAT3783 DFN34 package, solder the exposed paddle of
the IC onto the thermal landing of the PCB, where the
thermal landing is connected to the ground plane. This
AAT3783 has two exposed paddles (EP1 and EP2). EP1 is
connected to INCHR (pin 1) and EP2 is connected to GND
(pin 13). DO NOT make one whole thermal landing! If
heat is still an issue, multi-layer boards with dedicated
ground planes are recommended. Also, adding more
thermal vias on the thermal landing would help the heat
being transferred to the PCB effectively.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [e-mail] • www.skyworksinc.com
201903B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • April 27, 2012
17