AAT3686_08 Datasheet, PDF (15/23 Pages) Advanced Analogic Technologies – USB Port/AC Adapter Lithium-Ion/Polymer Battery Charger

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AAT3686
USB Port/AC Adapter Lithium-Ion/Polymer Battery Charger
is pulled to a voltage level above the V_USBSEL(H) threshold,
the USBH current level will be selected. Conversely, this
pin should be pulled below V_USBSEL(L) to enable the USBL
charge level. Typically, the two R_SETH and R_SETL resistors for
the USBH and USBL functions are fixed for 500mA and
100mA USB fast charge levels. However, these two
charge levels can be set to any level between 50mA and
500mA depending upon the system design requirements
for a given USB charge application. Refer to Table 1 and
Figure 3 for recommended R_SETH and R_SETL values.
10000
1000
USBL
100
USBH
ADPSET
10
1
10
100
1000
R_SET (kΩ)
Figure 3: I_FASTCHARGE vs. R_SET.
Protection Circuitry
Programmable Watchdog Timer
The AAT3686 contains a watchdog timing circuit for the
adapter input charging mode. No watchdog timing func-
tions are active for the USB input mode. Typically, a
0.1µF ceramic capacitor is connected between the CT pin
and ground. When a 0.1µF ceramic capacitor is used, the
device will time a shutdown condition if the trickle
charge mode exceeds 25 minutes and a combined trick-
le charge plus fast charge mode of three hours. When
the device transitions to the constant voltage mode, the
timing counter is reset and will time out after three
hours and shut down the charger (see Table 2).
Mode
Trickle Charge Time Out
Trickle Charge + Fast Charge (CC) Time Out
Constant Voltage (VC) Mode Time Out
Time
25 minutes
3 hours
3 hours
Table 2: Summary for a 0.1µF Used
for the Timing Capacitor.
The CT pin is driven by a constant current source and
will provide a linear response to increases in the timing
capacitor value. Thus, if the timing capacitor were to be
doubled from the nominal 0.1µF value, the time-out
times would be doubled.
If the programmable watchdog timer function is not
needed, it can be disabled by connecting the CT pin to
ground. The CT pin should not be left floating or un-
terminated, as this will cause errors in the internal tim-
ing control circuit.
The constant current provided to charge the timing
capacitor is very small, and this pin is susceptible to
noise and changes in capacitance value. Therefore, the
timing capacitor should be physically located on the
printed circuit board layout as closely as possible to the
CT pin. Since the accuracy of the internal timer is domi-
nated by the capacitance value, 10% tolerance or better
ceramic capacitors are recommended. Ceramic capacitor
materials, such as X7R and X5R type, are a good choice
for this application.
Over-Voltage Protection
An over-voltage event is defined as a condition where
the voltage on the BAT pin exceeds the maximum bat-
tery charge voltage and is set by the over-voltage pro-
tection threshold (V_OVP). If an over-voltage condition
occurs, the AAT3686 charge control will shut down the
device until voltage on the BAT pin drops below the over-
voltage protection threshold (V_OVP). The AAT3686 will
resume normal charging operation after the over-voltage
condition is removed. During an over-voltage event, the
STAT LEDs will report a system fault, and the actual fault
condition may be read via the DATA pin signal.
Over-Temperature Shutdown
The AAT3686 has a thermal protection control circuit
which will shut down charging functions should the inter-
nal die temperature exceed the preset thermal limit
threshold.
Battery Temperature Fault Monitoring
In the event of a battery over-temperature condition,
the charge control will turn off the internal pass device
and report a battery temperature fault on the DATA pin
function. The STAT LEDs will also display a system fault.
After the system recovers from a temperature fault, the
device will resume charging operation.
The AAT3686 checks battery temperature before start-
ing the charge cycle, as well as during all stages of
3686.2007.12.1.11
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