AAT3670 View Datasheet(PDF) - Analog Technology Inc
Part Name
Description
MFG CO.
'AAT3670' PDF : 32 Pages View PDF
drops to the programmed end of charge (EOC) cur-
rent, the charge cycle is complete and the charge
controller terminates the charging process.
The charge termination current is user pro-
grammed by the value of RTERM, which is connect-
ed between the TERM pin and ground. Use the
values listed in Table 1 to set the desired charge
termination current. The programmed charge ter-
mination current will remain at the same set level
regardless of which fast charge ADP, USBH or
USBL constant current mode is selected.
ITERM (mA)
320
174
125
95
77
64
58
50
49
42
37
RTERM (kΩ)
11.0
21.0
30.9
41.2
51.1
61.9
71.5
80.6
90.9
100.0
110.0
Table 1: Charge Termination Current
Programming Resistor Values.
If the desired end of charge termination current
level is not listed in Table 1, the TERM resistor
value may be calculated by the following equation:
For the Adapter input mode:
RTERM
=
K
·
⎛
⎝
VTERM⎞
ICC ⎠
Where:
K
= KI_TERM = 2000
VTERM = 2V
ICC = Fast charge constant current
The constants K and VTERM are specified in the
Typical Characteristics section of this datasheet.
The end-of-charge termination current function can
be disabled by pulling the TERM pin high via con-
necting the TERM pin to the BAT pin. In this state,
3670.2007.02.1.1
AAT3670
1.6A Dynamic Battery Charger
and Power Manager
the end-of-charge function will be disabled and the
battery will float charge in the constant voltage
mode indefinitely or until the cell voltage is brought
below the constant voltage threshold.
System Power Output
The power to the system is supplied via the OUT
pin. OUT will source power from either the ADP or
USB inputs when an external power source is
applied. When the battery charging function is com-
plete and the charging power source is removed,
the system will be powered from the battery via
Load Switch 3, referring to the AAT3670 block dia-
gram. The maximum current that can be supplied
from the ADP or USB inputs to a system load is
bounded by the user programmed ADPLIM and
USBLIM level. If the current consumption from the
system load exceeds that of the ADP or USB input
sources, the IC will draw current from the battery to
make up the difference as long as the battery cell
voltage remains above 2.9V. Power from the bat-
tery to the OUT pin is controlled by the ENBAT func-
tion. When the ENBAT is disabled the leakage cur-
rent from the battery to the load is less than 1µA.
Battery Connection and Battery Voltage
Sensing
Battery Connection
The single cell Li-ion battery should be connected
between the BAT pin and ground. The internal load
switching network will connect the battery to the
system load and apply the charging current.
Battery Voltage Sensing
The BATS pin is provided to employ an accurate volt-
age sensing capability to measure the terminal volt-
age at the battery cell being charged. This function
reduces measured battery cell voltage error between
the battery terminal and the charge control IC. The
AAT3670 charge control circuit will base charging
mode states upon the voltage sensed at the BATS
pin. The BATS pin must be connected to the battery
terminal for correct operation. If the battery voltage
sense function is not needed, the BATS pin should
be terminated directly to the BAT pin. If there is con-
cern of the battery sense function inadvertently
becoming an open circuit, the BATS pin may be ter-
minated to the BAT pin using a 10Ω resistor. Under
normal operation, the connection to the battery ter-
23
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