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Offset Calibration

Digital Magnitude Filter

Voltage

Temperature

RBI Input

bq27010, bq27210

SLUS707B – APRIL 2006 – REVISED JANUARY 2007

FUNCTIONAL DESCRIPTION (continued)

The offset voltage of the DSCC measurement must be very low to be able to measure small signal levels

accurately. The bqJUNIOR provides an auto-calibration feature to cancel the internal voltage offset error across

SRP and SRN for maximum charge measurement accuracy. NO CALIBRATION IS REQUIRED. External

voltage offset error caused by the PCB layout cannot be automatically calibrated out by the gauge, but the

external offset can be determined using a built-in user offset measurement command and can be programmed

into the EEPROM for inclusion in the offset compensation performed by the gauge. See the Layout

Considerations section for details on minimizing PCB induced offset across the SRP and SRN pins.

The bqJUNIOR auto-calibration of the DSCC offset is performed from time-to-time as operating conditions

change, to keep the measurement error small. A Calibration-In-Progress (CALIP) flag is set in FLAGS to indicate

when the operation occurs. Capacity, voltage, and temperature is updated during the 5.12 second offset

calibration time, but other parameters are not updated until the calibration has completed. When there is a full

reset, the gauge makes an initial quick offset calibration and delays the 5.12 second full offset calibration for at

least 40 seconds. This is done to prevent the full 5.12 second calibration operation from interfering with module

test functions that need to be performed immediately after power application during manufacturing test. The

quick offset calibration after a full reset is a 1.28 second offset measurment used as a delay, followed by a 1.28

use a slightly worse initial offset measurement, the tester may write bit 0 of CTRL (address 0x00) to 1 during the

first 1.28 seconds after the reset and the first offset sample will be used, cutting the initial quick offset calibration

time in half.

The Digital Magnitude Filter (DMF) threshold can be set in EEPROM to indicate a threshold below which any

charge or discharge accumulation is ignored. This allows setting a threshold above the maximum DSCC offset

expected from the IC and PCB combination, so that when no charge or discharge current is present, the

measured capacity change by the bqJUNIOR is zero. Note that even a small offset can add up to a large error

over a long period. In addition to setting the threshold above the largest offset expected, the DMF should be set

below the minimum signal level to be measured. The sense resistor value should be large enough to allow the

minimum current level to provide a signal level substantially higher than the maximum offset voltage.

Conversely, the sense resistor must be small enough to meet the system requirement for insertion loss as well

as keep the maximum voltage across the sense resistor below the 100 mV maximum that the DSCC can

accurately measure.

The DMF threshold is programmed in EEPROM in increments of 4.9 µV. Programming a zero in the DMF value

will disable the DMF function and all non-zero DSCC measurements are counted.

The bqJUNIOR monitors the battery voltage through the BAT pin and reports an offset corrected value through

the internal registers. The bqJUNIOR also monitors the voltage for the end-of-discharge (EDV) thresholds. The

EDV threshold levels are used to determine when the battery has been discharged to 6.25% or empty and

synchronizes the reported capacity to these levels when the programmed EDV thresholds are detected.

The bqJUNIOR uses an integrated temperature sensor to monitor the pack temperature and is reported through

the internal registers. The temperature measurement is used to adjust compensated available capacity and

self-discharge capacity loss.

The Register Backup Current (RBI) input pin is used with an external capacitor to provide backup potential to the

is absent. Register data will be maintained as long as the RBI voltage remains above 1.3 V.

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