Introduction
62
SLUUBD3D – September 2015 – Revised September 2018
Copyright © 2015–2018, Texas Instruments Incorporated
CEDV Gas Gauging
FCC also represents the full battery reference for the relative display mode and
RelativeStateOfCharge()
calculations.
The
DischargeCountRegister()
(DCR) register that tracks discharge of the battery. The bq78350-R1 uses
the DCR register to update the FCC register if the battery undergoes a qualified discharge from nearly full
to a low battery level. In this way, the bq78350-R1 learns the true discharge capacity of the battery under
system-use conditions.
The DCR counts up during discharge, independent of RC. DCR counts discharge activity, battery load
estimation, and self-discharge increments. The bq78350-R1 initializes DCR at the beginning of a
discharge to FCC – RC when RC is within the programmed value in
Near Full
. The DCR initial value of
FCC – RC is reduced by FCC/128 if
SC
= 1, and is not reduced if
SC
= 0. The DCR stops counting when
the battery voltage reaches the EDV2 threshold on discharge.
9.1.4 Initial Battery Capacity at Device Reset
The bq78350-R1 estimates the initial capacity of a battery pack at device reset, which is the case when
battery cell(s) are first attached to the application circuit. The initial FCC is a direct copy of
Full Charge
Capacity
. The initial RC and RSOC are estimated using the open-circuit voltage (OCV) characteristics of
the programmed Li-Ion chemistry (default ID1210),
DOD at EDV2
, and
Learned Full Charge Capacity
.
When assessing the RC vs. OCV correlation, the bq78350-R1 uses the applicable
CellVoltage1..15()
data
even if
ExtAveCellVoltage()
data is available. Upon the update of RC and RSOC based on the OCV data,
the
BatteryMode() [CF]
flag will be cleared. This gives a reasonably accurate RSOC; however, battery
capacity learning is required in order to determine the most accurate FCC, RC, and RSOC.
The determined value of remaining capacity can be further scaled, if needed, through the value of
RemCap Init Percent
. Upon a reset, the final value of
RemainingCapacity()
is initialized from the
RemCap Init Percent
value of the initial OCV correlated value. This value should be programmed to
match the scaling configured by
SpecificationInfo
.
Class
Subclass
Name
Format
Size in
Bytes
Min
Max
Default
Unit
Fuel
Gauging
CEDV Cfg
RemCap Init
Percent
Unsigned
Integer
1
0
110
100
%
During battery capacity learning,
Full Charge Capacity
and
DOD at EDV2
will be learned and updated.
Full Charge Capacity
should be initialized to the
Design Capacity
. DOD at EDV2 should be initialized to
(1 – (
Battery Low %
/ 100)) × 16384.
Class
Subclass
Name
Format
Size in
Bytes
Min
Max
Default
Unit
Fuel
Gauging
State
DOD at
EDV2
Integer
2
0
16384
15232
—
9.1.5 Capacity Learning (FCC Update)
The bq78350-R1 updates FCC with an amount based on the value in DCR if a qualified discharge occurs.
The new value for FCC equals the DCR value plus the value of nearly full and low battery levels, as
shown in the following equation:
FCC (new) = DCR (final) = DCR (initial) + Measured Discharge to EDV2 + (FCC × (
Battery Low %
/ 100))
The new value of FCC can be limited to not go above the
Design Capacity
value if
FCC_LIMIT
in
CEDV
Gauging Configuration
is set.
NOTE:
Learned Full Charge Capacity
limits an update to a minimum of 100.
