BQ2084-V140_14 Datasheet, PDF (14/64 Pages) Texas Instruments – SBS v1.1-COMPLIANT GAS GAUGE FOR USE WITH THE bq29312

bq2084-V140
SLUS664B – JULY 2005 – REVISED AUGUST 2006
www.ti.com
Self-Discharge
The bq2084-V140 estimates the self-discharge of the battery to maintain an accurate measure of the battery
capacity during periods of inactivity. The bq2084-V140 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)
Temp < 10
10 ≤ Temp <20
20 ≤ Temp <30
30 ≤ Temp <40
40 ≤ Temp <50
50 ≤ Temp <60
60 ≤ Temp <70
70 ≤ Temp
SELF-DISCHARGE RATE
1/4 Y% per day
½ Y% per day
Y% per day
2Y% per day
4Y% per day
8Y% per day
16Y% per day
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
Battery Electronic Load Compensation
The bq2084-V140 can be configured to compensate for a constant load (as from battery electronics) present in
the battery pack at all times. The bq2084-V140 applies the compensation continuously when the charge or
discharge is below the digital filter. The bq2084-V140 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
Midrange Capacity Corrections
The bq2084-V140 applies midrange capacity corrections when the VCOR bit is set in Gauge Configuration DF
0x29. The bq2084-V140 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.
For the midrange corrections to occur, the temperature must be in the range of 19°C to 31°C inclusive and
Current() and AverageCurrent() must both report between -64 mA and 0. The bq2084-V140 makes midrange
corrections as shown in Table 5. For a correction to occur, the bq2084-V140 must detect the need for correction
twice during subsequent 20-s intervals. With the VCOR bit set, the bq2084-V140 makes midrange corrections
whenever conditions permit.
If the OTVC bit in Gauge Configuration DF 0x29 is set and VCOR = 0, the bq2084-V140 makes two Voltage()
measurements, determines the average of the two readings and sets the appropriate RM level. No further
RSOC% vs Voltage() validation is performed until after the next device reset.
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