AAT3686
USB Port/AC Adapter
Lithium-Ion/Polymer Battery Charger
ADP
USBH
USBL
Ω Ω Ω
RSET (k ) RSET (k ) RSET (k )
ICC
USB
VUSB
50
75
N/A
N/A
86.6
57.6
42.2
21.0
13.7
10.2
8.06
6.65
5.62
4.87
4.32
3.83
3.48
3.16
2.87
2.67
2.43
86.6
57.6
42.2
20.5
13.7
10.2
8.06
6.65
5.62
4.87
4.32
3.83
3.48
3.16
2.87
2.67
2.43
R11
1.025M
100
200
300
400
500
600
700
800
900
1000
1100
1200
1300
1400
1500
84.5
43.2
28.0
21.0
16.9
13.3
11.5
10.2
9.09
8.06
7.32
6.65
6.04
5.62
5.36
CHR
VCHR = 2.0V
R12
825k
Figure 2: Internal Equivalent
Circuit for the CHR Pin.
Table 1: Resistor Values.
The USB charge reduction system becomes active
when the voltage on the USB input falls below the
USB charge reduction threshold (VUSBCHR), which
is typically 4.5V. Regardless of which USB charge
function is selected (USBH or USBL), the charge
reduction system will reduce the fast charge cur-
rent level in a linear fashion until the voltage
sensed on the USB input recovers above the
charge reduction threshold voltage. The USB
charge reduction threshold (VUSBCHR) can be exter-
nally set to a value lower than 4.5V by placing a
resistor divider network between VUSB and ground
with the center connected to the CHR pin. The USB
charge reduction feature can be disabled by con-
necting a 10kΩ resistor from the CHR pin directly
to the USB input pin (see Figure 2).
USB Input Charge Inhibit and Resume
The AAT3686 UVLO and power on reset feature
will function when the USB 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 USB pin or the
UVLO condition recovers, the system charge con-
trol will assess the state of charge on the battery
cell and will automatically resume charging in the
appropriate mode for the condition of the battery.
Enable / Disable
The AAT3686 provides an enable function to con-
trol the charger IC on and off. The enable (EN) pin
is active high. When pulled to a logic low level, the
AAT3686 will be shut down and forced into the
sleep state. Charging will be halted regardless of
the battery voltage or charging state. When the
device is re-enabled, the charge control circuit will
automatically reset and resume charging functions
with the appropriate charging mode based on the
battery charge state and measured cell voltage.
The following equation can be used to approximate a
USB charge reduction threshold below 4.5V:
R12
VUSBCHR = 2.0V ÷
R12 + R11
Where R11/R12 << 1MΩ.
14
3686.2006.10.1.9
AAT [ ADVANCED ANALOG TECHNOLOGY, INC. ]
