AAT3686_08 Datasheet, PDF (18/23 Pages) Advanced Analogic Technologies – USB Port/AC Adapter Lithium-Ion/Polymer Battery Charger

BatteryManager^TM
PRODUCT DATASHEET
AAT3686
USB Port/AC Adapter Lithium-Ion/Polymer Battery Charger
Data Timing
The system microcontroller should assert an active low
data request pulse for minimum duration of 200ns; this
is specified by the SQ_PULSE. Upon sensing the rising edge
of the end of the data request pulse, the AAT3686 status
data control will reply the data word back to the system
microcontroller after a delay defined by the data report
time specification T_DATA(RPT). The period of the following
group of data pulses will be defined by the T_DATA specifi-
cation.
Thermal Considerations
The AAT3686 is offered in a 3x4mm TDFN package and a
4x4mm TDFN package, each of which can provide up to
2.7W of power dissipation when it is properly bonded to
a printed circuit board and has a maximum thermal resis-
tance of 37°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 pack-
age in proximity to other heat generating devices in a
given application design. The ambient temperature
around the charger IC will also have an effect on the
thermal limits of a battery charging application. The
maximum limits that can be expected for a given ambient
condition can be estimated by the following discussion.
First, the maximum power dissipation for a given situa-
tion should be calculated:
Eq. 1: P_D = [(V_IN - V_BAT) · I_CC + (V_IN · I_OP)]
Where:
P_D = Total power dissipation by the device
V_IN = Either V_ADP or V_USB, depending on which mode is
selected
V_BAT = Battery voltage as seen at the BAT pin
I_CC = Maximum constant fast charge current pro-
grammed for the application
I_OP = 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 ther-
mal resistance of the 3x4mm and 4x4mm TDFN pack-
ages when sufficiently mounted to a PCB layout and the
internal thermal loop temperature threshold.
Where:
Eq. 2: T_A = T_J - (θ_JA · P_D)
T_A = Ambient temperature in degrees C
T_J = Maximum device junction temperature below the
thermal loop threshold
P_D = Total power dissipation by the device
θ_JA = Package thermal resistance in °C/W
Timing Diagram
SQ
CK
Data
SQ_PULSE
System Reset
System Start
T_SYNC
T_LAT
T_DATA(RPT) = T_SYNC + T_LAT < 2.5 P_DATA
T_OFF > 2 P_DATA
P_DATA
N=1
N=2
T_OFF
N=3
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