BQ2060SS-E411G4

bq2060 www.ti.com SLUS035E – JANUARY 2000 – REVISED OCTOBER 2005 SBS V1.1-COMPLIANT GAS GAUGE IC FEATURES • • • • • • • • • • Provides Accurate Measurement of Available Charge in NiCd, NiMH, Li-Ion, and Lead-Acid Batteries Supports SBS Smart Battery Data Specification v1.1 Supports the 2-Wire SMBus v1.1 Interface with PEC or 1-Wire HDQ16 Reports Individual Cell Voltages Monitors and Provides Control to Charge and Discharge FETs in Li-Ion Protection Circuit Provides 15-Bit Resolution for Voltage, Temperature, and Current Measurements Measures Charge Flow Using a V-to-F Converter with Offset of Less Than 16 µV After Calibration Consumes Less Than 0.5 mW Operating Drives a 4- or 5-Segment LED Display for Remaining Capacity Indication 28-Pin 150-mil SSOP DESCRIPTION The bq2060 SBS-compliant gas gauge IC for battery pack or in-system installation maintains an accurate record of available charge in rechargeable batteries. The bq2060 monitors capacity and other critical battery parameters for NiCd, NiMH, Li-ion, and lead-acid chemistries. The bq2060 uses a V-to-F converter with automatic offset error correction for charge and discharge counting. For voltage, temperature, and current reporting, the bq2060 uses an A-to-D converter. The onboard ADC also monitors individual cell voltages in a Li-ion battery pack and allows the bq2060 to generate control signals that may be used with a pack supervisor to enhance pack safety. The bq2060 supports the smart battery data (SBData) commands and charge-control functions. It communicates data using the system management bus (SMBus) 2-wire protocol or the Benchmarq 1-wire HDQ16 protocol. The data available include the battery’s remaining capacity, temperature, voltage, current, and remaining run-time predictions. The bq2060 provides LED drivers and a push-button input to depict remaining battery capacity from full to empty in 20% or 25% increments with a 4- or 5-segment display. The bq2060 works with an external EEPROM. The EEPROM stores the configuration information for the bq2060, such as the battery’s chemistry, self-discharge rate, rate compensation factors, measurement calibration, and design voltage and capacity. The bq2060 uses the programmable self-discharge rate and other compensation factors stored in the EEPROM to accurately adjust remaining capacity for use and standby conditions based on time, rate, and temperature. The bq2060 also automatically calibrates or learns the true battery capacity in the course of a discharge cycle from near full to near empty levels. The REG output regulates the operating voltage for the bq2060 from the battery cell stack using an external JFET. PIN CONNECTIONS HDQ16 ESCL ESDA RBI REG VOUT VCC VSS DISP LED1 LED2 LED3 LED4 LED5 1 2 3 4 5 6 7 8 9 10 11 12 13 14 28 27 26 25 24 23 22 21 20 19 18 17 16 15 SMBC SMBD VCELL4 VCELL3 VCELL2 VCELL1 SR1 SR2 SRC TS THON CVON CFC DFC 28-pin 150-mil SSOP These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam during storage or handling to prevent electrostatic damage to the MOS gates. Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet. PRODUCTION DATA information is current as of publication date. Products conform to specifications per the terms of the Texas Instruments standard warranty. Production processing does not necessarily include testing of all parameters. Copyright © 2000–2005, Texas Instruments Incorporated bq2060 www.ti.com SLUS035E – JANUARY 2000 – REVISED OCTOBER 2005 PIN DESCRIPTIONS TERMINAL NAME DESCRIPTION NO. HDQ16 1 Serial communication input/output. Open-drain bidirectional communications port ESCL 2 Serial memory clock. Output to clock the data transfer between the bq2060 and the external nonvolatile configuration memory ESDA 3 Serial memory data and address. Bidirectional pin used to transfer address and data to and from the bq2060 and the external nonvolatile configuration memory RBI 4 Register backup input. Input that provides backup potential to the bq2060 registers during periods of low operating voltage. RBI accepts a storage capacitor or a battery input. REG 5 Regulator output. Output to control an n-JFET for VCC regulation to the bq2060 from the battery potential VOUT 6 Supply output. Output that supplies power to the external EEPROM configuration memory VCC 7 Supply voltage input VSS 8 Ground. 9 Display control input. Input that controls the LED drivers LED1–LED5 DISP 10,11,12, 13,14 LED1-LED5 LED display segment outputs. Outputs that each may drive an external LED DFC 15 Discharge FET control output. Output to control the discharge FET in the Li-ion pack protection circuitry CFC 16 Charge FET controll output. Output to control the charge FET in the Li-ion pack protection circuitry CVON 17 Cell voltage divider controll output. Output control for external FETs to connect the cells to the external voltage dividers during cell voltage measurements THON 18 Thermistor bias control output. Output control for external FETs to connect the thermistor bias resistor during a temperature measurement TS 19 Thermistor voltage input. Input connection for a thermistor to monitor temperature SRC 20 Current sense input. Input to monitor instantaneous current SR1-SR2 VCELL1VCELL4 21,22 Charge-flow sense resistor inputs. Input connections for a small value sense resistor to monitor the battery charge and discharge current flow 23,24,25,2 Single-cell voltage inputs. Inputs that monitor the series element cell 6 voltages SMBD 27 SMBus data. Open-drain bidirectional pin used to transfer address and data to and from the bq2060 SMBC 28 SMBus clock. Open-drain bidirectional pin used to clock the data transfer to and from the bq2060 ORDERING INFORMATION For the most current package and ordering information, see the Package Option Addendum at the end of this document, or see the TI Web site at www.ti.com. 2 bq2060 www.ti.com SLUS035E – JANUARY 2000 – REVISED OCTOBER 2005 ABSOLUTE MAXIMUM RATINGS (1) SYMBOL PARAMETER MIN MAX UNIT V VCC–Supply voltage Relative to VSS –0.3 +6 VIN–All other pins Relative to VSS –0.3 +6 V TOPR Operating temperature –20 +70 °C TJ Junction temperature –40 +125 °C (1) NOTES Commercial Permanent device damage may occur if absolute maximum ratings are exceeded. Functional operation should be limited to the Recommended DC Operating Conditions detailed in this data sheet. DC ELECTRICAL CHARACTERISTICS (VCC = 2.7 V to 3.7 V, TOPR = –20°C to 70°C, unless otherwise noted) SYMBOL PARAMETER TEST CONDITIONS MIN TYP MAX 2.7 3.3 3.7 UNIT V 180 235 µA 5 10 µA 0.2 µA VCC Supply voltage ICC Operating current VOUT inactive ISLP Low-power storage mode current 1.5 V < VCC < 3.7 V ILVOUT VOUT leakage current VOUT inactive IVOUT VOUT source current VOUT active, VOUT = VCC– 0.6 V Output voltage low: LED1–LED5, CFC, DFC IOLS = 5 mA 0.4 V Output voltage low: THON, CVON IOLS = 5 mA 0.36 V –0.3 0.8 V 2 VCC+ 0.3 V 0.4 V – 0.3 0.8 V 1.7 6 V VOLS – 0.2 –5 mA VIL Input voltage low DISP VIH Input voltage high DISP VOL Output voltage low SMBC, SMBD, HDQ16, ESCL, ESDA VILS Input voltage low SMBC, SMBD, HDQ16, ESCL, ESDA VIHS Input voltage high SMBC, SMBD, HDQ16, ESCL, ESDA VAI Input voltage range VCELL1–4, TS, SRC IRB RBI data-retention input current VRBI RBI data-retention voltage 1.3 V ZAI1 Input impedance: SR1, SR2 0–1.25 V 10 MΩ ZAI2 Input impedance: VCELL1–4, TS, SRC 0–1.25 V 5 MΩ IOL = 1 mA VSS– 0.3 VRBI > 3 V, VCC < 2.0 V 10 1.25 V 50 nA VFC CHARACTERISTICS (VCC = 3.1 to 3.6 V, TOPR = –0°C to 70°C, Unless Otherwise Noted SYMBOL PARMETER TEST CONDITIONS VSR Input voltagerange,VSR2 and VSR1 VSR = VSR2– VSR1 VSROS VSR input offset VSR2 = VSR1, autocorrection disabled VSRCOS Calibrated offset RMVCO Supply voltage gain TYP –250 –50 –16 coefficient (1) RMTCO Temperature gain coefficient (1) INL Integral nonlinearity error VCC = 3.3 V 0.8 MAX UNIT +0.25 V 250 µV +16 µV 1.2 Slope for TOPR = –20°C to 70°C – 0.09 Total deviation TOPR = –20°C to 70°C –1.6% 0.1% –0.05 +0.05 Slope for TOPR = –0°C to 50°C Total deviation TOPR= –0°C to 50°C (1) MIN – 0.25 TOPR = 0°C –50°C –0.6% +0.09 %/V % /°C % /°C 0.1% 0.21% RMTCO total deviation is from the nominal gain at 25°C. 3 bq2060 www.ti.com SLUS035E – JANUARY 2000 – REVISED OCTOBER 2005 REG CHARACTERISTICS (TOPR = –20°C to 70°C) SYMBOL PARAMETER Normal Mode: REG controlled output voltage VRO Sleep Mode: REG controlled output voltage IREG TEST CONDITIONS JFET: Rds(on) < 150 Ω Vgs(off) < –3 V at 10 µA MIN TYP MAX 3.1 3.3 3.6 UNIT V 4.1 REG output current 1 µA SMBus AC SPECIFICATIONS VCC = 2.7 V to 3.7 V, TOPR = –20°C to 70°C, unless otherwise noted SYMBOL PARAMETER fSMB SMBus operating frequency Slave mode, SMBC 50% duty cycle fMAS SMBus master clock frequency Master mode, no clock low slave extend tBUF Bus free time between start and stop tHD:STA Hold time after (repeated) start tSU:STA Repeated start setup time tSU:STO Stop setup time tHD:DAT Data hold time tSU:DAT Data setup time tTIMEOUT Error signal/detect tLOW Clock low period tHIGH TEST CONDITIONS UNIT 100 kHz 51.2 kHz 4.7 µs µs µs 4 µs Receive mode 0 ns Transmit mode 300 ns 250 Clock high period See (2) tLOW:SEXT Cumulative clock low slave extend time See tLOW:MEXT Cumulative clock low master extend time See (4) MAX 4 (1) (3) TYP 10 4.7 See (1) (2) MIN ns 25 35 4.7 ms µs 4 50 µs (3) 25 ms (4) 10 ms The bq2060 times out when any clock low exceeds tTIMEOUT. tHIGH Max is minimum bus idle time. SMBC = SMBD = 1 for t > 50 ms causes reset of any transaction involving bq2060 that is in progress. tLOW:SEXT is the cumulative time a slave device is allowed to extend the clock cycles in one message from initial start to the stop. The bq2060 typically extends the clock only 20 ms as a slave in the read byte or write byte protocol. tLOW:MEXT is the cumulative time a master device is allowed to extend the clock cycles in one message from initial start to the stop. The bq2060 typically extends the clock only 20 ms as a master in the read byte or write byte protocol. HDQ16 AC SPECIFICATIONS () VCC = 2.7 V to 3.7 V, TOPR = –20°C to 70°C, unless otherwise noted SYMBOL PARAMETER TEST CONDITIONS MIN TYP MAX UNIT tCYCH Cycle time, host to bq2060 (write) 190 tCYCB Cycle time, bq2060 to host (read) 190 205 250 tSTRH Start hold time, host to bq2060 (write) 5 - - ns tSTRB Start hold time, host to bq2060 (read) 32 - - µs tDSU Data setup time - - 50 µs tDSUB Data setup time - - 50 µs tDH Data hold time 100 - - µs tDV Data valid time 80 - - µs tSSU Stop setup time - - 145 µs tSSUB Stop setup time - - 145 µs tRSPS Response time, bq2060 to host 190 - 320 µs t] Break time 190 - - µs tBR Break recovery time 40 - - µs 4 µs µs bq2060 www.ti.com SLUS035E – JANUARY 2000 – REVISED OCTOBER 2005 Figure 1. SMBus Timing Data tBR tB TD201803.eps Figure 2. HDQ16 Break Timing Write ”1” Write ”0” tSTRH tDSU tDH tSSU tCYCH Figure 3. HDQ16 Host to bq2060 Read ”1” Read ”0” tSTRB tDSUB tDV tSSUB tCYCB Figure 4. HDQ16 bq2060 to Host FUNCTIONAL DESCRIPTION GENERAL OPERATION The bq2060 determines battery capacity by monitoring the amount of charge input to or removed from a rechargeable battery. In addition to measuring charge and discharge, the bq2060 measures battery voltage, temperature, and current, estimates battery self-discharge, and monitors the battery for low-voltage thresholds. The bq2060 measures charge and discharge activity by monitoring the voltage across a small-value series sense resistor between the battery’s negative terminal and the negative terminal of the battery pack. The available battery charge is determined by monitoring this voltage and correcting the measurement for environmental and operating conditions. Figure 5 shows a typical bq2060-based battery pack application. The circuit consists of the LED display, voltage and temperature measurement networks, EEPROM connections, a serial port, and the sense resistor. The EEPROM stores basic battery pack configuration information and measurement calibration values. The EEPROM must be programmed properly for bq2060 operation. Table 10 shows the EEPROM memory map and outlines the programmable functions available in the bq2060. 5 bq2060 www.ti.com SLUS035E – JANUARY 2000 – REVISED OCTOBER 2005 FUNCTIONAL DESCRIPTION (continued) The bq2060 accepts an NTC thermistor (Semitec 103AT) for temperature measurement. The bq2060 uses the thermistor temperature to monitor battery pack temperature, detect a battery full charge condition, and compensate for self-discharge and charge/discharge battery efficiencies. MEASUREMENTS The bq2060 uses a fully differential, dynamically balanced voltage-to-frequency converter (VFC) for charge measurement and a sigma delta analog-to-digital converter (ADC) for battery voltage, current, and temperature measurement. Voltage, current, and temperature measurements are made every 2 to 2.5 seconds, depending on the bq2060 operating mode. Maximum times occur with compensated EDV, mWh mode, and maximum allowable discharge rate. Any AtRate computations requested or scheduled (every 20 seconds) may add up to 0.5 second to the time interval. 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 pins as shown in Figure 5. The VFC measures bipolar signals up to 250 mV. The bq2060 detects charge activity when VSR = VSR2 – VSR1 is positive and discharge activity when VSR = VSR2–VSR1 is negative. The bq2060 continuously integrates the signal over time using an internal counter. The fundamental rate of the counter is 6.25 µVh. Offset Calibration The bq2060 provides an auto-calibration feature to cancel the voltage offset error across SR1 and SR2 for maximum charge measurement accuracy. The calibration routine is initiated by issuing a command to ManufacturerAccess(). The bq2060 is capable of automatic offset calibration down to 6.25 µV. Offset cancellation resolution is less than 1 µV. Digital Filter The bq2060 does not measure charge or discharge counts below the digital filter threshold. The digital filter threshold is programmed in the EEPROM and should be set sufficiently high to prevent false signal detection with no charge or discharge flowing through the sense resistor. Voltage While monitoring SR1 and SR2 for charge and discharge currents, the bq2060 monitors the battery-pack potential and the individual cell voltages through the VCELL1–VCELL4 pins. The bq2060 measures the pack voltage and reports the result in the Voltage() register. The bq2060 can also measure the voltage of up to four series elements in a battery pack. The individual cell voltages are stored in the optional Manufacturer Function area. The VCELL1–VCELL4 inputs are divided down from the cells using precision resistors, as shown in Figure 5. The maximum input for VCELL1–VCELL4 is 1.25 V with respect to VSS. The voltage dividers for the inputs must be set so that the voltages at the inputs do not exceed the 1.25 V limit under all operating conditions. Also, the divider ratios on VCELL1–VCELL2 must be half of that of VCELL3–VCELL4. To reduce current consumption from the battery, the CVON output may used to connect the divider to the cells only during measurement period. CVON is high impedance for 250 ms (12.5% duty cycle) when the cells are measured, and driven low otherwise. See Table 1. Current The SRC input of the bq2060 measures battery charge and discharge current. The SRC ADC input converts the current signal from the series sense resistor and stores the result in Current(). The full-scale input range to SBC is limited to ±250 mV as shown in Table 2. 6 bq2060 www.ti.com SLUS035E – JANUARY 2000 – REVISED OCTOBER 2005 FUNCTIONAL DESCRIPTION (continued) VCC bq2060 LED1 REG LED2 VCC SST113 PACK+ VCC LED3 CVON LED4 VCELL4 LED5 VCELL3 CFC VCELL2 DFC VCELL1 DISP RBI VCC VOUT SRC SCL ESCL SR2 To Pack Protection Circuitry EEPROM A0 A1 A2 WP VSS R5 SDA ESDA SR1 VCC PACK− THON SMBC SMBC TS SMBD SMBD VSS HDQ16 Thermistor HDQ Figure 5. Battery Pack Application Diagram–LED Display and Series Cell Monitoring 7 bq2060 www.ti.com SLUS035E – JANUARY 2000 – REVISED OCTOBER 2005 Table 1. Example VCELL1–VCELL4 Divider and Input Range VOLTAGE INPUT VOLTAGE DIVISION RATIO FULL-SCALE INPUT (V) VCELL4 16 20 VCELL3 16 20 VCELL2 8 10 VCELL1 8 10 Table 2. SRC Input Range SENSE RESISTOR (Ω) FULL-SCALE INPUT (A) 0.02 ±12.5 0.03 ±8.3 0.05 ±5.0 0.10 ±2.5 Temperature The TS input of the bq2060 with an NTC thermistor measures the battery temperature as shown in Figure 5. The bq2060 reports temperature in Temperature(). THON may be used to connect the bias source to the thermistor when the bq2060 samples the TS input. THON is high impedance for 60 ms when the temperature is measured, and driven low otherwise. GAS GAUGE OPERATION General The operational overview in Figure 6 illustrates the gas gauge operation of the bq2060. Table 3 describes the bq2060 registers. The bq2060 accumulates a measure of charge and discharge currents and estimates self-discharge of the battery. The bq2060 compensates the charge current measurement for temperature and state-of-charge of the battery. The bq2060 also adjusts the self-discharge estimation based on temperature. Figure 6. bq2060 Operational Overview 8 bq2060 www.ti.com SLUS035E – JANUARY 2000 – REVISED OCTOBER 2005 The main counter RemainingCapacity() (RM) represents the available capacity or energy in the battery at any given time. The bq2060 adjusts RM for charge, self-discharge, and leakage compensation factors. The information in the RM register is accessible through the communications ports and is also represented through the LED display. The FullChargeCapacity() (FCC) register represents the last measured full discharge of the battery. It is used for the battery’s full-charge reference for relative capacity indication. The bq2060 updates FCC when the battery undergoes a qualified discharge from nearly full to a low battery level. FCC is accessible through the serial communications ports. The Discharge Count Register (DCR) is a non-accessible register that only tracks discharge of the battery. The bq2060 uses the DCR register to update the FCC register if the battery undergoes a qualified discharge from nearly full to a low battery level. In this way, the bq2060 learns the true discharge capacity of the battery under system-use conditions. Main Gas Gauge Registers RemainingCapacity() (RM) RM represents the remaining capacity in the battery. The bq2060 computes RM in either mAh or 10 mWh depending on the selected mode. On initialization, the bq2060 sets RM to 0. RM counts up during charge to a maximum value of FCC and down during discharge and self-discharge to 0. In addition to charge and self-discharge compensation, the bq2060 calibrates RM at three low-battery-voltage thresholds, EDV2, EDV1, and EDV0 and three programmable midrange thresholds VOC25, VOC50, and VOC75. This provides a voltage-based calibration to the RM counter. DesignCapacity() (DC) The DC is the user-specified battery full capacity. It is calculated from Pack Capacity EE 0x3a–0x3b and is represented in mAh or 10 mWh. It also represents the full-battery reference for the absolute display mode. FullChargeCapacity() (FCC) FCC is the last measured discharge capacity of the battery. It is represented in either mAh or 10 mWh depending on the selected mode. On initialization, the bq2060 sets FCC to the value stored in Last Measured Discharge EE 0x38–0x39. During subsequent discharges, the bq2060 updates FCC with the last measured discharge capacity of the battery. The last measured discharge of the battery is based on the value in the DCR register after a qualified discharge occurs. Once updated, the bq2060 writes the new FCC value to EEPROM in mAh to Last Measured Discharge. FCC represents the full-battery reference for the relative display mode and relative state of charge calculations. Discharge Count Register (DCR) The DCR register counts up during discharge, independent of RM. DCR can continue to count even after RM has counted down to 0. Prior to RM = 0, discharge activity, light discharge estimation and self-discharge increment DCR. After RM = 0, only discharge activity increments DCR. The bq2060 initializes DCR to FCC – RM when RM is within twice the programmed value in Near Full EE 0x55. The DCR initial value of FCC – RM is reduced by FCC/128 if SC = 0 (bit 2 in Control Mode) and is not reduced if SC = 1. DCR stops counting when the battery voltage reaches the EDV2 threshold on discharge. Capacity Learning (FCC Update) And Qualified Discharge The bq2060 updates FCC with an amount based on the value in DCR if a qualified discharge occurs. The new value for FCC equals the DCR value plus the programmable nearly full- and low-battery levels, according to the following equation: FCC(new)  DCR(final)  DCR(initial)
measureddischarge to EDV2
(FCCxBatteryLow%) (1) where: BatteryLow% = (value stored in EE 0x54) ÷ 2.56 9 bq2060 www.ti.com SLUS035E – JANUARY 2000 – REVISED OCTOBER 2005 A qualified discharge occurs if the battery discharges from RM ≥ FCC –Near Full * 2 to the EDV2 voltage threshold with the following conditions: • No valid charge activity occurs during the discharge period. A valid charge is defined as an input 10 mAh into the battery. • No more than 256 mAh of self-discharge and/or light discharge estimation occurs during the discharge period. • The temperature does not drop below 5°C during the discharge period. • The battery voltage reaches the EDV2 threshold during the discharge period and the voltage was less than the EDV2 threshold minus 256 mV when bq2060 detected EDV2. • No midrange voltage correction occurs during the discharge period. FCC cannot be reduced by more than 256 mAh or increased by more than 512 mAh during any single update cycle. The bq2060 saves the new FCC value to the EEPROM within 4 s of being updated. Table 3. bq2060 Register Functions FUNCTION COMMAND CODE SMBus ACCESS UNITS 0x00 read/write n/a 0x01 0x01 read/write mAh, 10 mWh 0x02 0x02 read/write minutes BatteryMode 0x03 0x03 read/write n/a SMBus HDQ16 ManufacturerAccess 0x00 RemainingCapacityAlarm RemainingTimeAlarm 10 AtRate 0x04 0x04 read/write mAh, 10 mWh AtRateTimeToFull 0x05 0x05 read minutes AtRateTimeToEmpty 0x06 0x06 read minutes AtRateOK 0x07 0x07 read Boolean Temperature 0x08 0x08 read 0.1°K Voltage 0x09 0x09 read mV Current 0x0a 0x0a read mA AverageCurrent 0x0b 0x0b read mA MaxError 0X0c 0X0c read percent RelativeStateOfCharge 0x0d 0x0d read percent AbsoluteStateOfCharge 0x0e 0x0e read percent RemainingCapacity 0x0f 0x0f read mAh, 10 mWh FullChargeCapacity 0x10 0x10 read mAh, 10 mWh RunTimeToEmpty 0x11 0x11 read minutes AverageTimeToEmpty 0x12 0x12 read minutes AverageTimeToFull 0x13 0x13 read minutes ChargingCurrent 0x14 0x14 read mA ChargingVoltage 0x15 0x15 read mV Battery Status 0x16 0x16 read n/a CycleCount 0x17 0x17 read cycles DesignCapacity 0x18 0x18 read mAh, 10 mWh DesignVoltage 0x19 0x19 read mV SpecificationInfo 0x1a 0x1a read n/a ManufactureDate 0x1b 0x1b read n/a Integer SerialNumber 0x1c 0x1c read Reserved 0x1d-0x1f 0x1d-0x1f - - ManufacturerName 0x20 0x20-0x25 read string DeviceName 0x21 0x28-0x2b read string DeviceChemistry 0x22 0x30-0x32 read string ManufacturerData 0x23 0x38-0x3b read string bq2060 www.ti.com SLUS035E – JANUARY 2000 – REVISED OCTOBER 2005 Table 3. bq2060 Register Functions (continued) FUNCTION COMMAND CODE SMBus HDQ16 SMBus ACCESS UNITS Pack Status 0x2f (LSB) 0x2f (LSB) read/write n/a Pack Configuration 0x2f (MSB) 0x2f (MSB) read/write n/a VCELL4 0x3c 0x3c read/write mV VCELL3 0x3d 0x3d read/write mV VCELL2 0x3e 0x3e read/write mV VCELL1 0x3f 0x3f read/write mV Table 4. State of Charge Based on Low Battery Voltage THRESHOLD STATE OF CHARGE IN RM EDV0 0% EDV1 3% EDV2 Battery Low % End-of-Discharge Thresholds And Capacity Correction The bq2060 monitors the battery for three low-voltage thresholds, EDV0, EDV1, and EDV2. The EDV thresholds are programmed in EDVF/EDV0 EE 0x72–0x73, EMF/EDV1 EE 0x74–0x75, and EDV C1/C0 Factor/ EDV2 EE 0x78–0x79. If the CEDV bit in Pack Configuration is set, automatic EDV compensation is enabled and the bq2060 computes the EDV0, EDV1, and EDV2 thresholds based on the values in EE 0x72–0x7d, 0x06, and the battery’s current discharge rate, temperature, capacity, and cycle count. The bq2060 disables EDV detection if Current() exceeds the Overload Current threshold programmed in EE 0x46 - EE 0x47. The bq2060 resumes EDV threshold detection after Current() drops below the overload current threshold. Any EDV threshold detected is reset after a 10-mAh charge is applied. The bq2060 uses the thresholds to apply voltage-based corrections to the RM register according to Table 4. The bq2060 adjusts RM as it detects each threshold. If the voltage threshold is reached before the corresponding capacity on discharge, the bq2060 reduces RM to the appropriate amount as shown in Table 4. If RM reaches the capacity level before the voltage threshold is reached on discharge, the bq2060 prevents RM from decreasing until the battery voltage reaches the corresponding threshold. Self-Discharge The bq2060 estimates the self-discharge of the battery to maintain an accurate measure of the battery capacity during periods of inactivity. The algorithm for self-discharge estimation takes a programmed estimate for the expected self-discharge rate at 25°C stored in EEPROM and makes a fixed reduction to RM of an amount equal to RemainingCapacity()/256. The bq2060 makes the fixed reduction at a varying time interval that is adjusted to achieve the desired self-discharge rate. This method maintains a constant granularity of 0.39% for each self-discharge adjustment, which may be performed multiple times per day, instead of once per day with a potentially large reduction. The self-discharge estimation rate for 25°C is doubled for each 10 degrees above 25°C or halved for each 10 degrees below 25°C. The following table shows the relation of the self-discharge estimation at a given temperature to the rate programmed for 25°C (Y% per day): TEMPERATURE (C) SELF-DISCHARGE RATE Temp < 10 ¼Y% per day 10 ≤ Temp