BQ2060SS Datasheet, PDF (41/59 Pages) Texas Instruments – SBS V1.1-COMPLIANT GAS GAUGE IC

bq2060
www.ti.com
SLUS035E – JANUARY 2000 – REVISED OCTOBER 2005
EEPROM PROGRAMMING (continued)
ADC
Sense
Resistor
Gain
+
625
(R_s)
(4)
The 16-bit VFC Sense Resistor Gain in EE 0x6a–0x6b scales each VFC interrupt to mAh. VFC Sense Resistor
Gain is based on the resistance of the series sense resistor. The following formula computes a nominal or
starting value for VFC Sense Resistor Gain from the sense resistor value.
VFC
Sense
Resistor
Gain
+
409.6
(R_s)
(5)
Sense resistor values are limited to the range of 0.00916 Ω to 0.100 Ω.
Digital Filter
The digital filter threshold, VDF (µV), is set by the value stored in Digital Filter EE 0x52.
Digital
Filter
+
2250
VDF
(6)
CELL CHARACTERISTICS
Battery Pack Capacity and Voltage
Pack capacity in mAh units is stored in Pack Capacity EE 0x3a–0x3b. In mAh mode, the bq2060 copies Pack
Capacity to DesignCapacity(). In mWh mode, the bq2060 multiplies Pack Capacity by Design Voltage EE
0x12–0x13 to calculate DesignCapacity() scaled to 10 mWh. Design Voltage is stored in mV.
The initial value for Last Measured Discharge in mAh is stored in EE 0x38–0x39. Last Measured Discharge is
modified over the course of pack usage to reflect cell aging under the particular use conditions. The bq2060
updates Last Measured Discharge in mAh after a capacity learning cycle. The bq2060 uses the Last Measured
Discharge value to calculate FullChargeCapacity() in mAh or 10mWh mode.
EDV Thresholds and Near-Full Percentage
The bq2060 uses three pack voltage thresholds to provide voltage-based warnings of low battery capacity. The
bq2060 uses the values stored in EEPROM for the EDV0, EDV1, and EDV2 values or calculates the three
thresholds from a base value and the temperature, capacity, and rate adjustment factors stored in EEPROM. If
EDV compensation is disabled then EDV0, EDV1, and EDV2 are stored directly in mV in EE 0x72–0x73, EE
0x74–0x75, and EE 0x78–0x79, respectively.
For capacity correction at EDV2, Battery Low % EE 0x54 can be set at a desired state-of-charge,
STATEOFCHARGE%, in the range of 5% to 20%. Typical values for STATEOFCHARGE% are 7%–12%
representing 7 –12% capacity.
Battery Low % + STATEOFCHARGE% 2.56
(7)
The bq2060 updates FCC if a qualified discharge occurs from a near-full threshold to EDV2. The desired
near-full threshold window, NFW (mAh), is programmed in Near Full in EE 0x55.
Near
Full
+
NFW
2
(8)
EDV Discharge Rate and Temperature Compensation
If EDV compensation is enabled, the bq2060 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
EDV0,1,2 + EMF F_BL * ^Ť I_LOAD ^Ť R0 F_TZ F_CY
(9)
where
•
•
EMF is a no-load battery voltage that is higher than the highest EDV threshold that is computed. EMF is
programmed in mV in EMF/EDV1 EE 0x74–0x75.
I_LOAD is the current discharge load.
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