AAT3673 Datasheet, PDF (18/28 Pages) Skyworks Solutions Inc. – 1.6A Dynamic Battery Charger and Power Manager

DATA SHEET
AAT3673
1.6A Dynamic Battery Charger and Power Manager
Temperature Sense (TS)
Inside the AAT3673, the internal battery temperature
sensing circuit is comprised of two comparators which
establish a voltage window for safe operation. The
thresholds for the TS operating window are bounded by
the TS1 and TS2 specifications. Referring to the Electrical
Characteristics table in this datasheet, the TS1 threshold
= 30% · V_BYP and the TS2 threshold = 60% · V_BYP. If the
use of the TS pin function is not required by the system,
it should be terminated to ground.
BYP
BYP
AAT3673
0.60 x V_BYP
TS
Battery Cold Fault
Battery
Pack
x V_BYP
Battery Hot Fault
Figure 2: AAT3673 Battery
Temperature Sensing Circuit.
Charge Safety Timer (CT)
While monitoring the charge cycle, the AAT3673 utilizes a
charge timer to help identify damaged cells and to ensure
that the cell is charged safely. Operation is as follows:
upon initiating a charging cycle, the AAT3673 charges the
cell at 10% of the programmed maximum charge until
V_BAT >2.9V. If the cell voltage fails to reach the precondi-
tioning threshold of 2.9V (typ) before the safety timer
expires, the cell is assumed to be damaged and the
charge cycle terminates. If the cell voltage exceeds 2.9V
prior to the expiration of the timer, the charge cycle pro-
ceeds into fast charge. There are two timeout periods: 50
minutes for Trickle Charge mode, and 6 hours for Constant
Current Mode and Constant Voltage mode altogether.
The CT pin is driven by a constant current source and will
provide a linear response to increases in the timing
capacitor value. The timeout is 7 hours (typical) using a
100nF capacitor for C_T. Thus, for a 200nF capacitor it
would be 14 hours, and for a 50nF capacitor it would be
3.5 hours respectively.
For a given target delay time T_D (in hours) calculate:
C_T
=
(T_D
·
100nF)
7
If the programmable watchdog timer function is not
needed, it can be disabled by terminating the CT pin to
ground. The CT pin should not be left floating or unter-
minated, as this will cause errors in the internal timing
control circuit. The constant current provided to charge
the timing capacitor is very small, and this pin is suscep-
tible 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 dominated
by the capacitance value, a 10% tolerance or better
ceramic capacitor is recommended. Ceramic capacitor
materials, such as X7R and X5R types, are a good choice
for this application.
System Operation Flowchart
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [e-mail] • www.skyworksinc.com
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201881B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • April 25, 2012