AAT3688
USB Port Lithium-Ion/Polymer Battery Charger
the AAT3688 status data control will reply the data
word back to the system microcontroller after a
delay specified by the data report time specification
TDATA(RPT). The period of the following group of data
pulses will be specified by the TDATA specification.
Data Timing
The system microcontroller should assert an active
low data request pulse for minimum duration of
200ns; this is specified by TLO(DATA). Upon sensing
the rising edge of the end of the data request pulse,
Timing Diagram
SQPULSE
PDATA
SQ
System Reset
System Start
CK
TSYNC
TLAT
TOFF
Data
TDATA(RPT) = TSYNC + TLAT < 2.5 PDATA
TOFF > 2 PDATA
N=3
N=1
N=2
Where:
Thermal Considerations
The AAT3688 is packaged in a Pb-free, 3x3mm
TDFN package which can provide up to 2.0W of
power dissipation when it is properly bonded to a
printed circuit board and has a maximum thermal
resistance of 50°C/W. Many considerations should
be taken into account when designing the printed
circuit board layout, as well as the placement of the
charger IC package in proximity to other heat gen-
erating devices in a given application design. The
ambient temperature around the charger IC will
also have an affect on the thermal limits of a bat-
tery charging application. The maximum limits that
can be expected for a given ambient condition can
be estimated by the following discussion.
PD = Total Power Dissipation by the Device
VIN = Input Voltage Level, VUSB
VBAT = Battery Voltage as Seen at the BAT Pin
ICC = Maximum Constant Fast Charge Current
Programmed for the Application
IOP = Quiescent Current Consumed by the
Charger IC for Normal Operation
Next, the maximum operating ambient temperature
for a given application can be estimated based on
the thermal resistance of the 3x3mm TDFN pack-
age when sufficiently mounted to a PCB layout and
the internal thermal loop temperature threshold.
First, the maximum power dissipation for a given
situation should be calculated:
TA = TJ - (θJA
· PD)
Eq. 5:
PD = [(VIN - VBAT) · ICC + (VIN · IOP)]
Eq. 4:
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3688.2006.10.1.5
AAT [ ADVANCED ANALOG TECHNOLOGY, INC. ]
