BQ2016 Datasheet, PDF (6/21 Pages) Texas Instruments – GAS GAUGE IC FOR HIGH DISCHARGE RATES

bq2016
GAS GAUGE IC FOR
HIGH DISCHARGE RATES
SLUS475A– JANUARY 2001 – REVISED NOVEMBER 2002
functional description
general operation
The bq2016 determines battery capacity by monitoring the amount of charge input to or removed from a
rechargeable battery. The bq2016 measures charge and discharge currents, estimates self-discharge, and
monitors the battery for low voltage and capacity thresholds. The bq2016 automatically compensates charge
and discharge currents for rate and temperature to adjust for battery efficiency under different conditions.
The bq2016 is configured to display capacity in a relative display mode. The display mode uses the last
measured discharge or learned capacity of the battery as the battery-full reference. The LED display can be
activated by a push-button connected to the DISP input or when the bq2016 detects a charge or discharge rate.
measurements
The bq2016 uses a fully differential, dynamically balanced voltage-to-frequency converter (VFC) for charge
measurement and a delta sigma analog-to-digital converter (ADC) for battery voltage, current, and temperature
measurement.
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. The VFC measures bipolar signals up to 250 mV in magnitude. The bq2016 detects
charge activity when V_SR = V_SR2 – V_SR1 is positive and a discharge activity when V_SR = V_SR2 – V_SR1 is negative.
The bq2016 integrates the signal over time using an internal counter. The bq2016 accumulates charge or
discharge at the rate of 3.125 µVh.
digital filter and VFC calibration
The bq2016 does not integrate charge or discharge counts below the digital filter threshold. The digital filter
threshold is set at 300 µV until a VFC calibration is performed. The calibration is performed after the first valid
charge after initialization. It takes up to 20 minutes to begin the calibration and up to 60 minutes to complete
the VFC calibration. The bq2016 suspends VFC calibration while it detects charge or discharge activity during
this period. After successful VFC calibration, the digital filter threshold is set to 100 µV.
voltage monitoring and thresholds
In conjunction with monitoring SR1 and SR2 for charge and discharge currents, the bq2016 monitors the battery
pack potential through the SB pin. The bq2016 measures the pack voltage and reports the result in the battery
voltage (VSBH:L) register. The bq2016 converts the signals at the SB input every 2 seconds.
The SB input is divided down from the cells using 1% tolerance resistors. To reduce current consumption from
the battery, the CVON output can switch the divider to the cells only during measurement period. CVON is high
impedance when the cells are measured, and driven low otherwise. The full-scale input for the SB pin is 1.25 V.
The bq2016 monitors the voltage at SB for the end-of-discharge voltage (EDV) and maximum voltage (MCV)
thresholds. The bq2016 uses the EDV threshold level to determine when the battery has reached an empty
state, and the MCV threshold level to detect a fault condition during charge. The EDV and MCV input levels are
set at:
EDV = 0.45 V
MCV = 1.00 V
The bq2016 disables EDV monitoring if V_SR is greater than the overload threshold. If the bq2016 detects an
overload threshold, the bq2016 sets the OLVD flag in the secondary status flags (FLAGS2) register. The bq2016
resumes EDV detection after V_SR drops back below the overload threshold. The overload threshold is a function
of battery capacity and is defined in the PFC table.
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