BQ2060A_15 Datasheet, PDF (7/61 Pages) Texas Instruments – SBS v1.1-Compliant Gas Gauge IC

bq2060A
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SLUS500D – OCTOBER 2001 – REVISED OCTOBER 2011
Figure 5 shows a typical bq2060A-based battery-pack application. The circuit consists of the LED display,
voltage and temperature measurement networks, EEPROM connections, a serial port, and the sense resistor.
The EEPROM stores basic battery-pack configuration information and measurement-calibration values. The
EEPROM must be programmed properly for bq2060A operation. Table 9 shows the EEPROM memory map and
outlines the programmable functions available in the bq2060A.
The bq2060A accepts an NTC thermistor (Semitec 103AT) for temperature measurement. The bq2060A uses the
thermistor temperature to monitor battery-pack temperature, detect a battery full-charge condition, and
compensate for self-discharge and charge/discharge battery efficiencies.
Measurements
The bq2060A uses a fully differential, dynamically balanced voltage-to-frequency converter (VFC) for charge
measurement and a sigma delta analog-to-digital converter (ADC) for battery voltage, current, and temperature
measurement.
Voltage, current, and temperature measurements are made every 2–2.5 seconds, depending on the bq2060A
operating mode. Maximum times occur with compensated EDV, mWh mode, and maximum allowable discharge
rate. Any AtRate computations requested or scheduled (every 20 seconds) may add up to 0.5 second to the time
interval.
Charge and Discharge Counting
The VFC measures the charge and discharge flow of the battery by monitoring a small-value sense resistor
between the SR₁ and SR₂ pins as shown in Figure 5. The VFC measures bipolar signals up to 250 mV. The
bq2060A detects charge activity when V_SR = V_SR2 – V_SR1 is positive and discharge activity when V_SR =
V_SR2 – V_SR1 is negative. The bq2060A continuously integrates the signal over time using an internal counter. The
fundamental rate of the counter is 6.25 µVh.
Offset Calibration
The bq2060A provides an auto-calibration feature to cancel the voltage offset error across SR₁ and SR₂ for
maximum charge measurement accuracy. The calibration routine is initiated by issuing a command to
Manufacturer Access(). The bq2060A is capable of automatic offset calibration down to 6.25 µV. Offset
cancellation resolution is less than 1 µV.
Digital Filter
The bq2060A does not measure charge or discharge counts below the digital filter threshold. The digital filter
threshold is programmed in the EEPROM and should be set sufficiently high to prevent false signal detection
with no charge or discharge flowing through the sense resistor.
Voltage
While monitoring SR₁ and SR₂ for charge and discharge currents, the bq2060A monitors the battery-pack
potential and the individual cell voltages through the VCELL₁ – VCELL₄ pins. The bq2060A measures the pack
voltage and reports the result in Voltage(). The bq2060A can also measure the voltage of up to four series
elements in a battery pack. The individual cell voltages are stored in the optional Manufacturer Function area.
The VCELL₁ – VCELL₄ inputs are divided down from the cells using precision resistors, as shown in Figure 5.
The maximum input for VCELL₁ – VCELL₄ is 1.25 V with respect to V_SS. The voltage dividers for the inputs must
be set so that the voltages at the inputs do not exceed the 1.25-V limit under all operating conditions. Also, the
divider ratios on VCELL₁ – VCELL₂ must be half of that of VCELL₃ – VCELL₄. To reduce current consumption
from the battery, the CVON output may be used to connect the divider to the cells only during measurement
period. CVON is high impedance for 250 ms (12.5% duty cycle) when the cells are measured, and driven low
otherwise (see Table 1).
The SRC input of the bq2060A measures battery charge and discharge current. The SRC ADC input converts
the current signal from the series sense resistor and stores the result in Current(). The full-scale input range to
SBC is limited to ±250 mV as shown in Table 2.
Copyright © 2001–2011, Texas Instruments Incorporated
Product Folder Link(s): bq2060A
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