AAT3685-1 Advanced Analog Technology, Inc., AAT3685-1 Datasheet - Page 13

• Manufacturer Part Number: AAT3685-1
• Description: Lithium-Ion/Polymer Battery Charger
• Manufacturer: Advanced Analog Technology, Inc.

BatteryManager
Application Information
USB System Power Charging
The USB charge mode provides two programmable fast
charge levels up to 1A for each, SETH and SETL. The
SETH or SETL modes may be externally selected by the
select pin (PWRSEL).
nected to a logic high level, the SETH level will be active.
Conversely, when PWRSEL is pulled to a logic low level
(ground), the SETL level will be used for fast charging.
These two charge levels may be user programmed to
any level between 50mA and 1A by selecting the appro-
priate resistor values for R
1 for recommended R
input constant current charge levels.
Charge Reduction
In many instances, product system designers do not
know the real properties of a potential port to be used
to supply power to the battery charger. Typical powered
USB ports commonly found on desktop and notebook
PCs should supply up to 500mA. In the event a port
being used to supply the charger is unable to provide the
programmed fast charge current, or if the system under
charge must also share supply current with other func-
tions, the AAT3685 will automatically reduce USB fast
charge current to maintain port integrity and protect the
host system.
The charge reduction system becomes active when the
voltage on the input falls below the charge reduction
threshold (V
of which charge function is selected (SETH or SETL), the
charge reduction system will reduce the fast charge cur-
rent level in a linear fashion until the voltage sensed on
the input recovers above the charge reduction threshold
voltage.
may be externally set to a value lower than 4.5V by
placing a resistor divider network between V
ground with the center connected to the CHR pin. The
charge reduction feature may be disabled by connecting
a 10kΩ resistor from the CHR pin directly to the ADP/
USB input pin.
The following equation may be used to approximate a
USB charge reduction threshold below 4.5V:
where R11/R12 << 1MΩ.
3685.2007.12.1.4
Eq. 1:
The charge reduction threshold (V
ADP/USB_CHR
V
ADP/USB_CHR
), which is typically 4.5V. Regardless
SETH
TM
When the PWRSEL pin is con-
and R
SETH
= 2.0V ÷
and R
SETL
values for the desired
R12 + R11
SETL
. Refer to Table
R12
ADP/USB
w w w . a n a l o g i c t e c h . c o m
ADP/USB_CHR
and
)
Input Charge Inhibit and Resume
The AAT3685 UVLO and power on reset feature will func-
tion when the input pin voltage level drops below the
UVLO threshold. At this point, the charger will suspend
charging and shut down. When power is re-applied to the
ADP/USB pin or the UVLO condition recovers, the system
charge control will assess the state of charge on the bat-
tery cell and will automatically resume charging in the
appropriate mode for the condition of the battery.
Single Path Charging from
a Line Adapter or USB Source
Most USB charging applications limit charging current to
500mA due to the limitations of a USB port as a power
source. The AAT3685 is capable of, and may be pro-
grammed for, constant current charge levels up to 1A.
Thus, charging operation is not just restricted to use
with USB port supplies. Any power source may be used
1000
100
200
300
400
500
600
700
800
900
I
Lithium-Ion/Polymer Battery Charger
50
75
CC
Figure 2: Internal Equivalent Circuit
Table 1: Recommended R
R11
R12
V
ADP/USB
for the CHR Pin.
R
CHR
PRODUCT DATASHEET
SET
SETH
86.6
57.6
42.2
21.0
13.7
10.2
8.06
6.65
5.62
4.87
4.32
3.83
(kΩ)
ADP/USB
AAT3685
825k
1.025M
V
CHR
= 2.0V
SET
Values.
R
SET
SETL
86.6
57.6
42.2
20.5
13.7
10.2
8.06
6.65
5.62
4.87
4.32
3.83
(kΩ)
13