DATA SHEET
AAT3682
Li-Ion/Polymer Linear Battery Charger
that the voltage at TS is within a voltage window bound-
ed by VTS1 and VTS2. Please see the following equations
for specifying resistors:
between BAT and VSS will control the output voltage
when the AAT3682 is powered up when no battery is
connected. The AAT3682 can become unstable if a high
impedance load is placed across the BAT pin to VSS.
Such a case is possible with aging li-ion/poly battery
cells. As cells age through repeated charge and dis-
charge cycles, the internal impedance can rise over time.
A 10μF or larger output capacitor will compensate for the
adverse effects of a high impedance load and assure
device stability over all operating conditions.
RT1 and RT2 for use with NTC Thermistor:
5 ∙ RTH ∙ RTC
3 · (RTC - RTH)
RT1
RT2
=
=
5 ∙ RTH
R
∙
TC
(2 ∙ RTC) - (7 ∙ RTH)
Power Dissipation
RT1 and RT2 for use with PTC Thermistor:
The voltage drop across the VP and BAT pins multiplied
times the charge current is used to determine the inter-
nal power dissipation. The maximum power dissipation
occurs when the input voltage is at a maximum and the
battery voltage is at the minimum preconditioning volt-
age threshold. This power is then multiplied times the
package theta to determine the maximum junction tem-
perature. The worst case power junction temperature is
calculated as follows:
5 ∙ RTH ∙ RTC
3 · (RTH - RTC)
RT1
RT2
=
=
5 ∙ RTH
R
∙
TC
(2 ∙ RTH) - (7 ∙ RTC)
Where RTC is the thermistor’s cold temperature resis-
tance and RTH is the thermistor’s hot temperature resis-
tance. See thermistor specifications for additional infor-
mation. To ensure there is no dependence on the input
supply changes, connect divider between VCC and VSS.
Disabling the temperature-monitoring function is
achieved by applying a voltage between VTS1 and VTS2 on
the TS pin.
PMAX = (VIN(MAX) - VSENSE - VSCHOTTKY - VBAT(MIN)) ⋅ ICHG(MAX)
= (5.5V - 0.1V - 0.2V - 3.04V) ⋅ 550mA
= 1.2W
This equation can be used to determine the maximum
input voltage given the maximum junction and ambient
temperature and desired charge current.
Capacitor Selection
TJ(MAX) - TAMB
θ ⋅ ICHG(MAX)
Input Capacitor
VIN(MAX)
=
=
+ VBAT + VSCHOTTKY + VCS
In general, it is good design practice to place a decou-
pling capacitor between the VCC and VSS pins. An input
capacitor in the range of 1μF to 10μF is recommended.
If the source supply is unregulated, it may be necessary
to increase the capacitance to keep the input voltage
above the under-voltage lockout threshold. If the
AAT3682 is to be used in a system with an external
power supply source, such as a typical AC-to-DC wall
adapter, then a CIN capacitor in the range of 10μF should
be used. A larger input capacitor in this application will
minimize switching or power bounce effects when the
power supply is “hot plugged” in.
120°C - 70°C
50°C/W ⋅ 500mA
+ 3.1V + 0.2V + 0.1V
= 5.3V
Operation Under No-Load
Under no-load conditions (i.e., when the AAT3682 is
powered with no battery connected between the BAT pin
and VSS), the output capacitor is charged up very quick-
ly by the trickle charge control circuit to the BAT pin until
the output reaches the recharge threshold (VRCH). At this
point, the AAT3682 will drop into sleep mode. The output
capacitor will discharge slowly by the capacitor’s own
internal leakage until the voltage seen at the BAT pin
drops below the VRCH threshold. This 100mV cycle will
Output Capacitor
The AAT3682 does not need an output capacitor for sta-
bility of the device itself. However, a capacitor connected
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
14
201884B
• Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • April 25, 2012
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