AAT3687 Datasheet, PDF (15/22 Pages) Advanced Analogic Technologies – Lithium-Ion/Polymer Battery Charger

AAT3687
Lithium-Ion/Polymer Battery Charger
Digital Charge Status Reporting
The AAT3687 has a comprehensive digital data
reporting system by use of the DATA pin feature.
This function can provide detailed information
regarding the status of the charging system. The
DATA pin is a bi-directional port which will read
back a series of data pulses when the system
microcontroller asserts a request pulse. This sin-
gle strobe request protocol will invoke one of 12
possible return pulse counts that the system micro-
controller can look up based on the serial report
data listed in Table 4.
The DATA pin function logic is active low and
should normally be pulled high to V_ADP. This data
line can also be pulled high to the same level as the
high state for the logic I/O port on the system
microcontroller. In order for the DATA pin control
circuit to generate clean, sharp edges for the data
output, and to maintain the integrity of the data tim-
ing for the system, the pull-up resistor on the data
line should be low enough in value so that the
DATA signal returns to the high state without delay.
If the pull-up resistor is too high, the strobe pulse
from the system microcontroller could exceed the
maximum pulse time and the DATA output control
could issue false status reports. A 1.5kΩ resistor is
recommended when pulling the DATA pin high to
5.0V on the V_ADP input. If the data line is pulled
high to a voltage level less than 5.0V, the pull-up
resistor can be calculated based on a recommend-
ed minimum pull-up current of 3mA. Use the fol-
lowing formula:
Eq. 4:
R_PULL-UP ≤
V_PULL-UP
3mA
1.8V to 5.0V
IN
AAT3687
Status
Control
OUT
DATA Pin
R_{PULL_UP}
GPIO
Figure 3: Data Pin Application Circuit.
IN
OUT
μP GPIO
Port
Data Timing
The system microcontroller should assert an active
low data request pulse for minimum duration of
200ns; this is specified by T_LO(DATA). Upon sensing
the rising edge of the end of the data request pulse,
the AAT3687 status data control will reply the data
word back to the system microcontroller after a
delay specified by the data report time specification
T_DATA(RPT). The period of the following group of
data pulses will be specified by T_DATA.
3687.2006.10.1.7
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