QMax happens when the discharge stops after verifying that no conditions were present that would cause the
QMax update to fail. The BQ28Z610-R2 has an option to have DOD@EOC be valid for QMax updates, which
means it is possible to update QMax with no rest periods at all (by having a charge termination followed by a
full discharge); however, this is only recommended for certain new chemistries. Fast QMax can be enabled in
either LEARN mode (
FAST_QMax_LRN
) or FIELD mode (
FAST_QMax_FLD
). The LEARN mode flag means
Fast QMax is only enabled in IT state “06”, and will be disabled once 0E is reached. FIELD mode is enabled in
both “06” and “0E” states.
6.4.4 QMax and Fast QMax Update Boundary Check
The BQ28Z610-R2 implements a QMax and Fast QMax check prior to saving the value to data flash. This
improves the robustness of the QMax update in case of potential QMax corruption during the update process.
The verifications are as follows:
1. Verify that the updating QMax or Fast QMax value is within
QMaxDelta
, which is the maximum allowed
QMax change for each update. If the updating value is outside of this data flash parameter, the BQ28Z610-
R2 caps the change to
QMaxDelta
of the Design Capacity.
2. Bound the absolute QMax value,
QMax Upper Bound
. This is the maximum allowed QMax value over the
lifetime of the pack.
3. Ensure that QMax is greater than 0 before saving to data flash.
6.4.5 Ra Table Initial Values
The Ra table is part of the impedance profile that updates during discharge when gauging is enabled. The
initial
Cell0 R_a0...14
,
Cell1 R_a0...14
, values should be programmed by selecting the correct chemistry data
during data flash configuration. A chemistry database is constantly updating, and can be downloaded from the
Gas Gauge Chemistry Updater product web page (
http://www.ti.com/tool/gasgaugechem-sw
). The initial
xCell0
R_a0...14
,
xCell1 R_a0...14
values are a copy of the non-x data set. Two sets of Ra tables are used alternatively
when gauging is enabled to prevent wearing out the data flash.
The
Cell0 R_a Flag
,
Cell1 R_a Flag
, and the
xCell0 R_a Flag
,
xCell1 R_a Flag
, indicate the validity of the cell
impedance table for each cell. Firmware updates these values: It is not recommended to change them manually.
High Byte
Low Byte
0x00
Cell impedance and QMax
updated
0x00
Table not used and QMax
updated
0x05
RELAX mode and QMax update
in progress
0x05
RSVD
0x55
DISCHARGE mode and cell
impedance updated
0x55
Table being used
0xFF
Cell impedance never updated
0xFF
Table never used, no QMax or
cell impedance update
6.4.6 Ra Table Update Conditions
The impedance is different across different DOD states. Each cell has 15 Ra grid points presenting the
impedance from 0%–100% DOD. In general, the Ra table is updated during discharge. The
GaugingStatus[RX]
flag will toggle when the Ra grid point is updated. The Ra update is disabled if any of the following conditions are
met. The
GaugingStatus[R_DIS]
is set to indicate the Ra update is disabled.
• During the optimization cycle, the Ra update is disabled until QMax is updated (that is, Ra will not be updated
if Update Status = 4) OR
• Ra update is disabled if the charge accumulation error > 2% of Design Capacity OR
• During a discharge, a bad Ra value is calculated:
– A negative Ra is calculated or
– A bad RaScale value is calculated.
A valid OCV reading during RELAX mode or a fast QMax update without an OCV read will clear the
[R_DIS]
flag.
Gauging
40
BQ28Z610-R2
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