Datasheet

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Watch Dog Re-Initialization
Self-Discharge
Battery Electronic Load Compensation
Midrange Capacity Corrections
bq2084-V143
SLUS732 – SEPTEMBER 2006
specific applications, this new aging factor may be required. In those cases, experimental data must be taken at
the 0, 100, 200, and 300 cycle read points using a typical discharge rate while at ambient temperature. Entering
this data into a TI provided MathCAD program will yield the appropriate DF: Age Factor value. Contact TI
Applications Support @ http://www-k.ext.ti.com/sc/technical-support/email-tech-support.asp?AAP for more
detailed information.
The bq2084-V143 adds a new feature which periodically tests the state of two registers required to produce the
32kHz signal to the AFE.
The two registers which configure a 32kHz clock output to the AFE are checked once per second in normal
operation, sleep mode, and permanent failure mode. If the register contents are incorrect, they are corrected, up
to a maximum number of corrections, as set by a new data flash configuration constant called Max 32k Reinit.
After the maximum number of corrections has been exceeded, if the 32kHz clock output is lost, then a watchdog
failure (WDF) occurs in the AFE. As a result of the WDF, the AFE turns all the FETS off. At this point the WDF
can only be corrected by a full reset.
The bq2084-V143 estimates the self-discharge of the battery to maintain an accurate measure of the battery
capacity during periods of inactivity. The bq2084-V143 makes self-discharge adjustments to RM every 1/4 s
when awake and periodically (determined by Sleep Timer DF 0xfe) when in sleep mode. The self-discharge
estimation rate for 25 ° C is doubled for each 10 degrees above 25 ° C or halved for each 10 degrees below 25 ° C.
Table 4 shows the relation of the self-discharge estimation at a given temperature to the rate programmed for
25 ° C (Y% per day programmed in DF 0x2d).
Table 4. Self-Discharge for Rate Programmed
TEMPERATURE ( ° C) SELF-DISCHARGE RATE
Temp < 10 1/4 Y% per day
10 ≤ Temp <20 ½ Y% per day
20 ≤ Temp <30 Y% per day
30 ≤ Temp <40 2Y% per day
40 ≤ Temp <50 4Y% per day
50 ≤ Temp <60 8Y% per day
60 ≤ Temp <70 16Y% per day
70 ≤ Temp 32Y% per day
The nominal self-discharge rate, %PERDAY (% per day), is programmed in an 8-bit value Self-Discharge Rate
DF 0x2d by the following relation:
Self-Discharge Rate = %PERDAY/ 0.01
The bq2084-V143 can be configured to compensate for a constant load (as from battery electronics) present in
the battery pack at all times. The bq2084-V143 applies the compensation continuously when the charge or
discharge is below the digital filter. The bq2084-V143 applies the compensation (BEL) in addition to
self-discharge. The compensation occurs at a rate determined by the value stored in Electronics Load DF 0x2e.
The compensation range is 0 µA-765 µA in steps of approximately 3 µA . The data is stored as follows:
Electronics Load = BEL / 3
The bq2084-V143 applies midrange capacity corrections when the VCOR bit is set in Gauge Configuration DF
0x29. The bq2084-V143 adjusts RM to the associated percentage at three different voltage levels: VOC25,
VOC50, and VOC75 . The VOC values represent the open-circuit battery voltage at which RM corresponds to the
associated percentage for each threshold.
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