Introduction
65
SLUUBD3D – September 2015 – Revised September 2018
Copyright © 2015–2018, Texas Instruments Incorporated
CEDV Gas Gauging
The bq78350-R1 uses the EDV thresholds to apply voltage-based corrections to the RC register according
to the content in
Table 9-1. State-of-Charge Based on Low Battery Voltage
Threshold
Relative State-of-Charge (RSOC)
EDV0
0%
EDV1
3%
EDV2
Battery Low %
The bq78350-R1 performs EDV-based RC adjustments with
Current()
≥
C/32. No EDVs are set if
Current()
< C/32. The bq78350-R1 adjusts RC as it detects each threshold. If the voltage threshold is
reached before the corresponding capacity on discharge, the bq78350-R1 reduces RC to the appropriate
amount, as shown in
If an RC % level is reached on discharge before the voltage reaches the corresponding threshold, then
RC is held at that % level until the threshold is reached. RC is only held if [VDQ] = 1, indicating a valid
learning cycle is in progress. If
Battery Low %
is set to 0, EDV1 and EDV0 corrections are disabled.
9.1.8 Reserve Capacity
The bq78350-R1 can provide an additional programmable quantity of capacity in "reserve"; that is, when
RC = 0, then there is still
Reserve Capacity
left. This value is required to be entered and scaled to match
the settings of IPSCALE and CapM settings.
The value of
Reserve Capacity
is subtracted from the learn capacity when determining the value of the
reported FCC. This means when RSOC = 0% (EDV0), then there is still some capacity left for critical
system actions. It is strongly recommended that when determining the value for Reserve Capacity that the
setting of
Battery Low %
is still considered to ensure the appropriate setting of the EDV2 voltage on the
discharge curve. For example: If Reserve Capacity ~1% of
Design Capacity
, then the typical value for
Battery Low %
would be 6%.
Class
Subclass
Name
Format
Size in
Bytes
Min
Max
Default
Unit
Fuel
Gauging
CEDV Cfg
Reserve
Capacity
Integer
2
0
32767
0
mAh
9.1.9 EDV Discharge Rate and Temperature Compensation
If EDV compensation is enabled,
CEDV
= 1, the bq78350-R1 calculates battery voltage to determine
EDV0, EDV1, and EDV2 thresholds as a function of battery capacity, temperature, and discharge load.
The general equation for EDV0, EDV1, and EDV2 calculation is as follows:
EDV0,1,2 = n (EMF × FBL – |ILOAD| × R0 × FTZ)
•
EMF is a no-load cell voltage higher than the highest cell EDV threshold computed. EMF is
programmed in mV in
EMF
.
•
ILOAD is the current discharge load magnitude.
•
n = the number of series cells. In the bq78350-R1 case n = 1.
•
FBL is the factor that adjusts the EDV voltage for battery capacity and temperature to match the no-
load characteristics of the battery.
FBL = f (C0, C + C1, T)
•
C (either 0%, 3%, or
Battery Low %
for EDV0, EDV1, and EDV2, respectively) and C0 are the
capacity related EDV adjustment factors. C0 is programmed in
EDV C0 Factor
. C1 is the desired
residual battery capacity remaining at EDV0 (RC = 0). The C1 factor is stored in
EDV C1 Factor
.
•
T is the current temperature in °K.
•
R0•FTZ represents the resistance of a cell as a function of temperature and capacity.
