AAT3672 Datasheet, PDF (16/27 Pages) Skyworks Solutions Inc. – 1.6A Dynamic Battery Charger and Power Manager

DATA SHEET
AAT3672
1.6A Dynamic Battery Charger and Power Manager
varies in order to maintain the adapter input current.
I_{CH_CC} = I_BAT + I_BAT-OUT
For example: If R_SET = 57.6kΩ, the fast charge current
is set for 1A. For a system load of 0mA, the battery
charge current is 1A. As the system load is increased
the battery charge current is reduced, until the system
load is equal to 1A and the battery charge current is 0A.
Further increases in the system load will result in the
battery supplying the balance of the current; a system
load of 1.2A requires the battery to supply 0.2A.
In the second case, the ADP-BAT switch, the BAT-OUT
switch and the ADP-OUT switch are all enabled. Under
this condition, the adapter input current is limited inter-
nally to 1.6A minimum (I_{LIM_ADP}) and is split between the
system load (I_ADP-OUT) and the battery charge current
(I_{CH_CC}). The charge current is dynamically adjusted as
the system load varies in order to maintain the adapter
input current at or below the 1.6A minimum.
I_{LIM_ADP} ≥ I_{CH_CC} + I_ADP-OUT
For example: If R_SET = 57.6kΩ, the fast charge current
is set for 1A. For a system load of 0mA, the battery
charge current is 1A and the adapter current is less than
1.6A. As the system load is increased the battery charge
current is 1A, until the system load is equal to 0.6A and
the adapter input current is 1.6A. Increasing the system
load above 0.6A causes the battery charge current to be
reduced, until the system load is equal to 1.6A and the
battery charge current is 0A. Further increases in the
system load will result in the battery supplying the bal-
ance of the current; a system load of 1.8A requires the
battery to supply 0.2A.
Temperature Sense (TS)
Inside the AAT3672, the internal battery temperature
sensing system is comprised of two comparators which
establish a voltage window for safe operation. The thresh-
olds for the TS operating window are bounded by the TS1
and TS2 specifications. Referring to the electrical charac-
teristics table in this datasheet, the TS1 threshold = 0.30
· V_ADP and the TS2 threshold = 0.60 · V_ADP. If the use of
the TS pin function is not required by the system, it
should be terminated to ground using a 10kΩ resistor.
VADP
ADP
TS
Battery
Pack
AAT3672
0.60 x VADP
Battery Cold Fault
x VADP
Battery Hot Fault
Figure 2: AAT3672 Battery Temperature
Sense Circuit.
Charge Safety Timer (CT)
While monitoring the charge cycle, the AAT3672 utilizes
a charge safety 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 AAT3672
charges the cell at 10% of the programmed maximum
charge until V_BAT >2.9V. If the cell voltage fails to the
precondition 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
proceeds into fast charge. There are two timeout peri-
ods: about 50 minutes for Trickle Charge mode, 6 hours
for Constant Current (CC) mode and Constant Voltage
(CV) mode altogether.
The timeout is 7 hours (typical) for a C_T = 100nF capac-
itor. Timeout is directly proportional to capacitor value,
so for a 200nF capacitor it would be 14 hours, and for a
50nF capacitor it would be 3.5 hours.
For a given target delay time T_D (in hours) calculate:
C_T
=
(T_D
·
100nF)
7
The CT pin is driven by a constant current source and
provides a linear response to increases in the timing
capacitor value.
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
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [e-mail] • www.skyworksinc.com
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201880B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • April 25, 2012