AAT3673 Datasheet, PDF (23/28 Pages) Skyworks Solutions Inc. – 1.6A Dynamic Battery Charger and Power Manager

DATA SHEET
AAT3673
1.6A Dynamic Battery Charger and Power Manager
The counter input frequency will be divided by two in the
event of a fault condition. Such fault conditions include
digital thermal loop charge current reduction, battery
charge reduction, and battery current sharing with the
output during the charging cycle. When the fault condition
recovers, the counter will resume the timing function.
The charge timer will automatically reset when the
AAT3673 enable pin is reset or cycled off and on. The
constant current provided to charge the timing capacitor
is very small and this pin is susceptible to noise and
changes in capacitance value. Therefore, the timing
capacitor should be physically located on the printed
circuit board layout as close as possible to the CT pin.
Since the accuracy of the internal timer is determined by
the capacitance value, a 10% tolerance or better ceram-
ic capacitor is recommended. Ceramic capacitor materi-
als such as X7R and X5R type are a good choice for this
application.
Battery Over-Voltage Protection
An over-voltage event is defined as a condition where
the voltage on the BAT pin exceeds the maximum bat-
tery charge voltage and is set by the over-voltage pro-
tection threshold (V_BOVP). If an over-voltage condition
occurs, the AAT3673 charge control will shutdown the
device until voltage on the BAT pin drops below the over-
voltage protection threshold (V_BOVP). The AAT3673 will
resume normal charging operation once the battery
over-voltage condition is removed.
Over-Temperature Shutdown
The AAT3673 has a thermal protection control circuit
which will shut down charging functions should the inter-
nal die temperature exceed the preset thermal limit
threshold. Thermal shutdown also turns off the switches
from ADP to OUT and BAT to OUT.
Battery Temperature Fault Monitoring
In the event of a battery over- or under-temperature
condition, the charge control will turn off the internal
charge path regulation device and disable the BAT-OUT
dynamic path. After the system recovers from a tem-
perature fault, the device will resume charging opera-
tion. The AAT3673 checks battery temperature before
starting the charge cycle, as well as during all stages of
charging. Typically, batteries employ the use of a nega-
tive temperature coefficient (NTC) thermistor that is
integrated into the battery.
Capacitor Selection
Input Capacitor
A 1μF or larger capacitor is typically recommended for
C_ADP. C_ADP should be located as close to the device ADP
pin as practically possible. Ceramic, tantalum, or alumi-
num electrolytic capacitors may be selected for C_ADP.
There is no specific capacitor equivalent series resistance
(ESR) requirement for C_ADP. However, for higher current
operation, ceramic capacitors are recommended for C_ADP
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 1206 are available which
can meet these requirements. Other voltage rating
capacitor can also be used for the known input voltage
application.
Charger Output Capacitor
The AAT3673 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.
System Power Output Capacitor
For proper load voltage regulation and operational stabil-
ity, a capacitor is required between OUT and GND. The
output capacitor connection to the ground pin should be
made as directly as practically possible for maximum
device performance. Since the regulator has been
designed to function with very low ESR capacitors, a 10μF
ceramic capacitor is recommended for best performance.
Printed Circuit Board
Layout Recommendations
For proper thermal management and to take advantage
of the low R_DS(ON) of the AAT3673, a few circuit board
layout rules should be followed: IN and BAT 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
AAT3673 TDFN4x4 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. 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 transfer heat to
the PCB effectively.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [e-mail] • www.skyworksinc.com
201881B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • April 25, 2012
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