Corrections for the rate of discharge are made by adjust-
ing an internal discharge compensation factor. The dis-
charge factor is based on the dynamically measured V
The compensation factors during discharge are:
Table 2. Self-Discharge Compensation
< 50 mV
> 50 mV
> 100 mV
> 150 mV
> 253 mV
Temperature compensation during discharge also takes place.
At lower temperatures, the compensation factor increases by
0.05 for each 10°C temperature step below 10°C.
Comp. factor = 1.00 + (0.05 * N)
Where N = number of 10°C steps below 10°C and
T > 10°C: Nominal compensation, N = 0
0°C < T < 10°C: N = 1 (i.e., 1.00 becomes 1.05)
-10°C < T < 0°C: N = 2 (i.e., 1.00 becomes 1.10)
-20°C < T < -10°C: N = 3 (i.e., 1.00 becomes 1.15)
-20°C < T < -30°C: N = 4 (i.e., 1.00 becomes 1.20)
The LMD is susceptible to error on initialization or if no up-
dates 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 oc-
curs and LMD is updated (see the DCR description on page
7). 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.
A Capacity Inaccurate counter (CPI) is maintained and
incremented 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 ca-
pacity inaccurate flag (CI) is set if LMD has not been
updated following 64 valid charges.
The self-discharge compensation is programmed for a
nominal rate of
* NAC per day. This is the rate for a
battery within the 20–30°C temperature range (TMPGG
= 6x). This rate varies across 8 ranges from <10°C to
>70°C, doubling with each higher temperature step
(10°C). See Table 2
Table 3 illustrates the current-sensing error as a func-
tion of V
. A digital filter eliminates charge and
discharge counts to the NAC register when V
) is between -400µV and 500µV.
Table 3. bq2011 Current-Sensing Errors
Add 0.1% per °C above or below 25°C
and 1% per volt above or below 4.25V.
Measurement repeatability given
similar operating conditions.
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