BQ29330 Datasheet, PDF (12/26 Pages) Texas Instruments – 2-,3-,AND 4-CELL LITHIUM-ION OR LITHIUM-POLYMER BATTERY PROTECTION AFE

bq29330
SLUS673A – SEPTEMBER 2005 – REVISED DECEMBER 2005
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FUNCTIONAL DESCRIPTION (continued)
OVERLOAD, SHORT CIRCUIT IN CHARGE AND SHORT CIRCUIT IN DISCHARGE RESPONSE
When an overload, short circuit in charge, or short circuit in discharge fault is detected, the FETs are turned off.
The STATUS (b0…b3) register reports the details of overload, short circuit in charge or short-circuit discharge.
The respective STATUS (b0…b3) bits are set to 1 and the XALERT output is triggered. This condition is latched
until the STATE_CONTROL (b7) is set and then reset. If a FET is turned on after resetting STATE_CONTROL
(b0) and the error condition is still present on the system, then the device again enters the protection response
state.
2-, 3-, or 4-CELL CONFIGURATION
In a 2-cell configuration, VC1 and VC2 are shorted to VC3. In a 3-cell configuration, VC1 is shorted to VC2.
CELL VOLTAGE
The cell voltage is translated to allow a system host to measure individual series elements of the battery. The
series element voltage is translated to a GND-based voltage equal to 0.15 ±0.003 of the series element voltage.
This provides a range from 0 to 4.5 V. The translation output is presented between CELL+ and CELL– pins of
the bq29330 and is inversely proportional to the input using the following equation.
Where, V_(CELLOUT) = –K × V_(CELLIN) + 0.975 (V)
Programming CELL_SEL (b1, b0) selects the individual series element. The CELL_SEL (b3, b2) selects the
voltage monitor mode, cell monitor, offset, etc.
CALIBRATION OF CELL VOLTAGE MONITOR AMPLIFIER GAIN
The cell voltage monitor amplifier has an offset, and to increase accuracy, this can be calibrated.
The following procedure shows how to measure and calculate the offset as an example.
Step 1
Set CAL1=1, CAL0=1, VMEN=1.
VREF is trimmed to 0.975 V within ±1%; measuring VREF eliminates its error.
Measure internal reference voltage VREF from VCELL directly.
VREF = measured reference voltage
Step 2
Set CAL1=0, CAL0=1, CELL1=0, CELL0=0, VMEN=1.
The output voltage includes the offset and represented by:
V_OUT(4-5) = VREF + (1 + K) × V_OS (V)
Where K = CELL Scaling Factor
V_OS = Offset voltage at input of the internal operational amplifier
Step 3
Set CAL1=1, CAL0=0, CELL1=0, CELL0=0, VMEN=1.
Measure scaled REF voltage through VCELL amplifier.
The output voltage includes the scale factor error and offset and is represented by:
V_(OUTR) = VREF + (1 + K) × VOS – K × VREF (V)
Step 4
Calculate (V_OUT(4-5)– V_(OUTR)) / VREF.
The result is the actual scaling factor, K_ACT and is represented by:
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