Texas Instruments bq78350-R1

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SLUUBD3D–September 2015–Revised September 2018
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CEDV Gas Gauging
FTZ = f (R1, T0, C + C1, TC)
• R0 is the first order rate dependency factor stored in EDV R0 Factor (DF).
• T is the current temperature. C is the battery capacity relating to EDV0, EDV1, and EDV2.
• R1 adjusts the variation of impedance with battery capacity. R1 is programmed in EDV R1 Rate
Factor.
• T0 adjusts the variation of impedance with battery temperature. T0 is programmed in EDV T0 Rate
Factor.
• TC adjusts the variation of impedance for cold temperatures T < TC is programmed in EDV TC Factor.
• Typical values for the EDV compensation factors, based on overall pack voltages for a 3s2p Li-lon
18650 pack, are
– EMF = 11550/3
– T0 = 4475
– C0 = 235
– C1 = 0
– R0 = 5350/3
– R1 = 250
– TC = 3
The graphs below show the calculated EDV0, EDV1, and EDV2 thresholds versus capacity using the
typical compensation values for different temperatures and loads for a Li-Ion 18650 cell. The
compensation values vary widely for different cell types and manufacturers and must be matched exactly
to the unique characteristics for optimal performance.
Figure 9-3. (a) EDV Calculations vs Various Temperatures, (b) EDV Calculations vs Capacity for Various
Loads
9.1.10 EDV Age Factor
EDV Age factor allows the bq78350-R1 to correct the EDV detection algorithm to compensate for cell
aging. This parameter scales cell impedances as the cycle count increases. This factor is used to
accommodate for much higher impedances observed in larger capacity and/or aged cells.
For most Li-Ion and Li-Polymer applications, the default value of zero is sufficient. However, for Lithium
Iron Phosphate, a value of 18 is recommended.