Gas Gauging
13
SLUUBE8 – September 2018
Copyright © 2018, Texas Instruments Incorporated
General Description
1.1.11 CEDV Smoothing
The bq34210-Q1 device has the ability to smooth the
RemainingCapacity()
during discharge in order to
avoid a drop in
RelativeStateOfCharge()
when the EDV thresholds are reached. This feature is enabled by
setting the
Smoothing Config [SMEN]
= 1 and configuring the
Smoothing Start Voltage
and
Smoothing Delta Voltage
.
The smoothing will activate only when all of the following conditions are true:
•
Current()
< 0
•
Voltage()
<
Smoothing Start Voltage
•
EDV2 has been reached (
[EDV2]
= 1) OR (
Voltage()
– present EDV2 threshold) <
Smoothing Delta
Voltage
.
•
Maximum
Voltage()
during the previous one minute is less than the maximum
Voltage()
during the
current minute (that is, "drop rate" is greater than 0).
•
RemainingCapacity()
is greater than the capacity at the next EDV point.
While smoothing is active, the "drop rate" is used to estimate the time to the EDV point under the
assumption that the rate is constant (linear). This information is then used to estimate how much current
would need to be applied in order to have
RemainingCapacity()
reach the expected capacity at the EDV
point. The actual
Current()
is then scaled by the "smoothing current." This will either speed up or slow
down the
RemainingCapacity()
accumulation to reach the EDV threshold at the correct time.
Whenever the
RemainingCapacity()
accumulation is actively scaled, the
OperationStatus()[SMTH]
bit will
be set.
Smoothing deactivates whenever an EDV threshold is reached until the rate to the next EDV threshold
can be calculated; however, smoothing past the EDV2 point only occurs if
Smoothing Config [SMEXT]
is
set to 1.
To improve smoothing at the end of discharge, the SME0 configuration bit provides additional flexibility.
This is particularly useful when
FIXED_EDV0
is set and the calculated EDV2/EDV1 is lower than EDV0. In
this scenario, the State-of-Charge (SOC) smooths to EDV2, then to EDV1, and then to EDV0, leading to
SOC jumps. If the SME0 bit is set, then the SOC smooths directly to EDV0, leading to a smooth transition
to empty.
shows the available smoothing configurations.
Table 1-2. Smoothing Configurations
Smoothing Config
[SMEN]
Smoothing Config
[SMEXT]
CEDV Config
[SME0]
Description
0
0
0
No Smoothing
0
0
1
No Smoothing
0
1
0
No Smoothing
0
1
1
No Smoothing
1
0
0
Smoothing to EDV2
1
0
1
Smoothing to EDV0 if calculated EDV2/EDV1 is less than EDV0.
1
1
0
Smoothing to EDV2
≥
EDV1
≥
EDV0
1
1
1
Smoothing to EDV0 if calculated EDV2/EDV1 is less than EDV0.
The bq34210-Q1 device can also add smoothing during charging. In situations when the FCC is not
updated during a discharge cycle or on a subsequent charge cycle, if the valid charge termination is
reached, RSOC is synced to 100% regardless of the true RSOC. To help in scenarios like these, the
device enables the
SMOOTHEOC_EN
bit (default is enabled). When enabled, the RSOC value is
gradually increased to 100% instead of a sudden jump if the following are true:
a. Battery is charging.
b. Cell Voltage > Taper Voltage
c.
Charge Current
is decreasing AND is below the
EOC Smooth Current
threshold for
EOC Smooth
Current Time
.
