BQ2012_15 Datasheet, PDF (8/26 Pages) Texas Instruments – Gas Gauge IC With Slow-Charge Control

Not Recommended For New Designs
bq2012
Self-Discharge Estimation
The bq2012 continuously decrements NAC and increments
DCR for self-discharge based on time and temperature.
The self-discharge count rate is programmed to be a nomi-
nal
1
64
*
NAC
or
1
47
*
NAC
per
day
or
disabled
as
selected
by PROG5. This is the rate for a battery whose tempera-
ture is between 20°–30°C. The NAC register cannot be
decremented below 0.
Count Compensations
The bq2012 determines fast charge when the NAC up-
dates at a rate of ≥2 counts/sec. Charge and discharge are
compensated for temperature and charge/discharge
rate before updating the NAC and/or DCR. Self-dis-
charge estimation is compensated for temperature be-
fore updating the NAC or DCR.
Charge Compensation
Two charge efficiency compensation factors are used for
trickle charge and fast charge. Fast charge is defined as
a rate of charge resulting in ≥ 2 NAC counts/sec (≥ 0.15C
to 0.32C depending on PFC selections; see Table 2). The
compensation defaults to the fast charge factor until the
actual charge rate is determined.
Temperature adapts the charge rate compensation factors
over three ranges between nominal, warm, and hot tem-
peratures. The compensation factors are shown below.
Charge
Temperature
<30°C
30–40°C
> 40°C
Trickle Charge
Compensation
0.80
0.75
0.65
Fast Charge
Compensation
0.95
0.90
0.80
Discharge Compensation
Corrections for the rate of discharge are made by adjusting
an internal discharge compensation factor. The discharge
factor is based on the dynamically measured VSR. The
compensation factors during discharge are:
Approximate
VSR Threshold
VSR > -150 mV
VSR < -150 mV
Discharge
Compensation
Factor
1.00
1.05
Efficiency
100%
95%
Temperature compensation during discharge also takes place.
At lower temperatures, the compensation factor increases by
0.05 for each 10°C temperature range below 10°C.
Compensation factor = 1.0 + (0.05 _* N)
Where N = Number of 10°C steps below 10°C and
-150mV < VSR < 0.
For example:
T > 10°C : Nominal compensation, N = 0
0°C < T < 10°C: N = 1 (i.e., 1.0 becomes 1.05)
-10°C < T < 0°C: N = 2 (i.e., 1.0 becomes 1.10)
-20°C < T < -10°C: N = 3 (i.e., 1.0 becomes 1.15)
-20°C < T < -30°C: N = 4 (i.e., 1.0 becomes 1.20)
Self-Discharge Compensation
The self-discharge compensation is programmed for a
nominal
rate
of
1
64
*
NAC
or
1
47
*
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 tem-
perature step (10°C). See Table 3.
Table 3. Self-Discharge Compensation
Temperature
Step
< 10°C
10–20°C
20–30°C
30–40°C
40–50°C
50–60°C
Typical Rate
PROG5 = Z
PROG5 = L
NAC
256
NAC
128
NAC
64
NAC
32
NAC
16
NAC
8
NAC
188
NAC
94
NAC
47
NAC
23.5
NAC
11.8
NAC
5.88
Digital Magnitude Filter
The bq2012 has a programmable digital filter to eliminate
charge and discharge counting below a set threshold. The de-
fault setting is -0.30mV for VSRD and +0.38mV for VSRQ. The
proper digital filter setting can be calculated using the following
equation. Table 4 shows typical digital filter settings.
VSRD (mV) = -45 / DMF
VSRQ (mV) = -1.25 _* VSRD
Table 4. Typical Digital Filter Settings
DMF
75
100
150 (default)
175
200
DMF
Hex.
4B
64
96
AF
C8
VSRD
(mV)
-0.60
-0.45
-0.30
-0.26
-0.23
VSRQ
(mV)
0.75
0.56
0.38
0.32
0.28
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