AAT3697IWP-4.2-T1 Advanced Analog Technology, Inc., AAT3697IWP-4.2-T1 Datasheet - Page 14

• Manufacturer Part Number: AAT3697IWP-4.2-T1
• Description: 2A Lithium-Ion/Polymer Battery Charger
• Manufacturer: Advanced Analog Technology, Inc.

R
Where R
resistance and R
ture resistance. See thermistor specifications for
information. To ensure there is no dependence on
the input supply changes, connect the divider
between V
ture-monitoring function is achieved by applying a
voltage between V
Battery Charge Status Indication
The AAT3697 indicates the status of the battery
under charge with two different systems. First, the
device has two status LED driver outputs. These
two LEDs can indicate simple functions such as no
battery charge activity, battery charging, charge
complete, and charge fault. The AAT3697 also
provides a bi-directional data reporting function so
that a system microcontroller can interrogate the
DATA pin and read any one of 12 system states.
Status Indicator Display
Simple system charging status states can be dis-
played using one or two LEDs in conjunction with
the STAT1 and STAT2 pins on the AAT3697.
These two pins are simple open drain switches
used to connect the LED cathodes to ground. It is
1. Flashing rate depends on output capacitance.
14
T1
Event Description
Charge Disabled or Low Supply
Charge Enabled Without Battery
Battery Charging
Charge Completed
Fault
and R
Eq. 3:
TC
T2
ADP
for use with PTC Thermistor
is the thermistor's cold temperature
and GND. Disabling the tempera-
R
R
TH
T1
T2
TS1
is the thermistor's hot tempera-
=
=
and V
3 ⋅ (R
(2 ⋅ R
5 ⋅ R
5 ⋅ R
TH
TH
TH
TS2
) - (7 ⋅ R
TH
- R
⋅ R
on the TS pin.
⋅ R
TC
TC
)
TC
TC
Table 3: LED Status Indicator.
)
2A Lithium-Ion/Polymer Battery Charger
not necessary to use both display LEDs if a user
simply wants to have a single lamp to show "charg-
ing" or "not charging."
This can be accomplished by using the STAT1 pin
and a single LED. Using two LEDs and both STAT
pins simply gives the user more information to the
charging states. Refer to Table 3 for LED display
definitions. The LED anodes should be connected
to V
The LEDs should be biased with as little current as
necessary to create reasonable illumination; there-
fore, a ballast resistor should be placed between
the LED cathodes and the STAT1/2 pins. LED cur-
rent consumption will add to the overall thermal
power budget for the device package, hence it is
good to keep the LED drive current to a minimum.
2mA should be sufficient to drive most low-cost
green or red LEDs.
exceed 8mA for driving an individual status LED.
The required ballast resistor values can be esti-
mated using the following formulas:
Example:
Note: Red LED forward voltage (V
2.0V @ 2mA
Eq. 5:
ADP
.
Eq. 4:
R
STAT1
Flash
B(STAT1)
Off
On
Off
On
R
B(STAT1/2)
1
=
(5.5V - 2.0 V)
It is not recommended to
=
2mA
(V
I
ADP
LED(STAT1/2)
AAT3697
- V
STAT2
Flash
On
On
Off
Off
F(LED)
= 1.75kΩ
F
3697.2007.02.1.1
) is typically
1
)