AAT2550 Datasheet, PDF (21/35 Pages) Advanced Analogic Technologies – Total Power Solution for Portable Applications

AAT2550
Total Power Solution for Portable Applications
Data Timing
The system microcontroller should assert an active
low data request pulse for minimum duration of
200ns; this is specified by the S_QPULSE. Upon sens-
ing the rising edge of the end of the data request
pulse, the AAT2550 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 specification.
Timing Diagram
SQ
CK
Data
S_QPULSE
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
Capacitor Selection
Input Capacitor
In general, it is good design practice to place a
decoupling capacitor between the ADP pin and
ground. An input capacitor in the range of 1µF to
22µF 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 during device
enable and when battery charging is initiated.
If the AAT2550 adapter input is to be used in a sys-
tem with an external power supply source, such as
a typical AC-to-DC wall adapter, then a C_IN capaci-
tor 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."
Output Capacitor
The AAT2550 only requires a 1µF ceramic capac-
itor on the BAT pin to maintain circuit stability. This
value should be increased to 10µF or more if the
battery connection is made any distance from the
charger output. If the AAT2550 is to be used in
applications where the battery can be removed
from the charger, such as in the case of desktop
charging cradles, an output capacitor greater than
10µF may be required to prevent the device from
cycling on and off when no battery is present.
2550.2006.07.1.0
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