BQ2016 Datasheet, PDF (13/21 Pages) Texas Instruments – GAS GAUGE IC FOR HIGH DISCHARGE RATES

bq2016
GAS GAUGE IC FOR
HIGH DISCHARGE RATES
SLUS475A– JANUARY 2001 – REVISED NOVEMBER 2002
discharge compensation (continued)
The bq2016 adjusts the discharge-compensation efficiency for temperature. At lower temperatures, the
discharge-efficiency factor decreases by 5% for each 10°C temperature step below 10°C.
F_{DE (new)} = F_DE – (5% × N)
where N = number of 10°C steps below 10°C.
For example at a 1C discharge,
T > 10°C:
0°C < T < 10°C:
–10°C < T < 0°C:
–20°C < T < –10°C:
–20°C < T < –30°C:
error summary
N = 0 and F_DE(NEW) = 100%
N = 1 and F_DE(NEW) = 95%
N = 2 and F_DE(NEW) = 90%
N = 3 and F_DE(NEW) = 85%
N = 4 and F_DE(NEW) = 80%
capacity inaccurate
The LMD is susceptible to error on initialization or if no updates occur. On initialization, the LMD value includes
the error between the programmed full capacity and the actual capacity. This error is present until a valid
discharge occurs and LMD is updated. The other cause of LMD error is battery wear-out. As the battery ages,
the measured capacity must be adjusted to account for changes in actual battery capacity. The bq2016
increments the capacity inaccurate count (CPI) register each time a valid charge occurs and is reset whenever
LMD is updated from the DCR. The counter does not wrap around but stops counting at 255. The capacity
inaccurate flag (CI) is set if LMD has not been updated following 64 valid charges.
display
The bq2016 can directly display capacity information using low-power LEDs. The bq2016 displays the battery
charge as a percentage of the LMD.
The capacity display is also adjusted for the present battery temperature. The temperature adjustment reflects
the available capacity at a given temperature but does not affect the NAC register. Tables 6 and 7 show the
temperature adjustments:
Table 6. Temperature Translation for NiCd
TEMPERATURE
(C)
T ≥ 10
10 > T ≥ 0
0 > T ≥ –10
–10 > T ≥ –20
T < –20
TEMPERATURE TRANSLATION
(%)
100
100
90
75
50
Table 7. Temperature Translation for NiMH
TEMPERATURE
(C)
T ≥ 10
10 > T ≥ 0
0 > T ≥ –10
–10 > T ≥ –20
T < –20
TEMPERATURE TRANSLATION
(%)
100
75
40
0
0
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