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BQ2945SN-C409TR Datasheet(PDF) 9 Page - Texas Instruments |
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BQ2945SN-C409TR Datasheet(HTML) 9 Page - Texas Instruments |
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9 / 32 page  the current drops below 256mA and the voltage is less than 105% of ChargingVoltage. n Overcurrent: An overcurrent fault exists when the bq2945 measures a charge current more than 25% above the ChargingCurrent. If the ChargingCurrent is less than 1024mA, an overcurrent fault exists if the charge current is more than 256mA above the ChargingCurrent. When the bq2945 detects an overcurrent condition, the requested charge current is set to 0 and the Terminate_Charge_Alarm bit is set in Battery Status. The alarm bit is cleared when the current drops below 256mA. n Maximum Temperature: When the battery temperature exceeds the programmed maximum temperature, the requested charge current is set to zero and the Over_Temp_Alarm and the Terminate_Charge_Alarm bits are set in Battery Status. The alarm bits are cleared when the temperature drops below 50 °C. n Low Temperature: When the battery temperature is less than 0 °C, the requested charge current is set to the maintenance rate. Once the temperature is above 5 °C, the requested charge current is set to the fast rate. n Undervoltage: When the battery voltage is below the EDVF threshold, the requested charge current is set to the maintenance rate. Once the voltage is above EDVF, the requested charge current is set to the fast rate. Count Compensations Charge activity is compensated for temperature and state-of-charge before updating the RM and/or DCR. Self-discharge estimation is compensated for tempera- ture before updating RM or DCR. Charge Compensation Charge efficiency is compensated for state-of-charge, temperature, and battery chemistry. The charge effi- ciency is adjusted using the following equations: 1.) RM RM * Q Q EFC ET =− () where RelativeStateOfCharge < FullChargePercentage, and Q EFC is the programmed fast-charge efficiency vary- ing from 0.75 to 1.0. 2.) RM RM Q Q ETC ET =− *( ) where RelativeStateOfCharge ≥ FullChargePercentage and Q ETC is the programmed maintenance (trickle) charge efficiency varying from 0.75 to 1.0. Q ET is used to adjust the charge efficiency as the battery temperature increases according to the following: Qif T ET =< 030 °C QC T C ET =° ≤ < ° 002 30 40 .if QT C ET =≥ ° 005 40 .if QET is 0 over the entire temperature range for Li-Ion. Digital Magnitude Filter The bq2945 has a programmable digital filter to elimi- nate charge and discharge counting below a set threshold, VSRD. Table 2 shows typical digital filter settings. The proper digital filter setting can be calcu- lated using the following equation. DMF = 45 VSRD Error Summary Capacity Inaccurate The FCC is susceptible to error on initialization or if no updates occur. On initialization, the FCC value includes the error between the design capacity and the actual ca- pacity. This error is present until a qualified discharge occurs and FCC is updated (see the DCR description). The other cause of FCC error is battery wear-out. As the battery ages, the measured capacity must be ad- justed to account for changes in actual battery capacity. Periodic qualified discharges from full to empty will minimize errors in FCC. Current-Sensing Error Table 3 illustrates the current-sensing error as a function of VSR. A digital filter eliminates charge and discharge counts to the RM register when -VSRD <VSRO <+VSRD. Display The bq2945 can directly display capacity information using low-power LEDs. The bq2945 displays the battery charge state in either absolute or relative mode. In rela- tive mode, the battery charge is represented as a per- centage of the FCC. Each LED segment represents 20% of the FCC. 9 bq2945 DMF DMF Hex. VSRD (mV) 75 4B 0.60 100 64 0.45 150 96 0.30 175 AF 0.26 200 C8 0.23 Table 2. Typical Digital Filter Settings |
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