bq2016

GAS GAUGE IC FOR

HIGH DISCHARGE RATES

SLUS475A– JANUARY 2001 – REVISED NOVEMBER 2002

6

POST OFFICE BOX 655303

• DALLAS, TEXAS 75265

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 VSR = VSR2 – VSR1 is positive and a discharge activity when VSR = VSR2 – VSR1 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 VSR 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 VSR drops back below the overload threshold. The overload threshold is a function

of battery capacity and is defined in the PFC table.