bq2945 Gas Gauge IC with SMBus Interface Features General Description ➤ Provides accurate measurement of available charge in NiCd, NiMH, and Li-Ion batteries The bq2945 Gas Gauge IC With SMBus Interface is intended for battery-pack or in-system installation to maintain an accurate record of available battery charge. The bq2945 directly supports capacity monitoring for NiCd, NiMH, and Li-Ion battery chemistries. ➤ Supports SBS v1.0 data set and two-wire interface ➤ Two programmable general purpose output ports for added flexibility ➤ Designed for battery pack integration - Low operating current Complete circuit can fit on less than ¾ square inch of PCB space ➤ Supports SBS charge control commands for NiCd, NiMH, and Li-Ion ➤ Drives a five-segment LED display for remaining capacity indication The bq2945 uses the System Management Bus v1.0 (SMBus) protocol and supports the Smart Battery Data (SBData) commands. The bq2945 also supports the SBData charge control functions. Battery state-of-charge, remaining capacity, remaining time, and chemistry are av ai la b le ov er t h e s er ia l lin k . Battery-charge state can be directly indicated using a five-segment LED display to graphically depict battery full-to-empty in 20% increments. The bq2945 estimates battery selfdischarge based on an internal timer and temperature sensor and user-programmable rate information stored in external EEPROM. The bq2945 also automatically recalibrates or “learns” battery capacity in the full course of a discharge cycle from full to empty. The bq2945 may operate directly from three nickel chemistry cells. With the REF output and an external transistor, a simple, inexpensive regulator can be built to provide VCC for other battery cell configurations. An external EEPROM programs initial values into the bq2945 and is necessary for proper operation. ➤ 16-pin narrow SOIC Pin Connections Pin Names VCC 3.0–6.5V SR Sense resistor input LED1 LED segment 1/ EEPROM clock DISP Display control input SB Battery sense input LED2 LED segment 2/ EEPROM data CP2 Control pin 2 VCC 1 16 VOUT LED1/ESCL 2 15 REF LED2/ESDA 3 14 SMBC LED3 4 13 SMBD LED3 LED segment 3 SMBD SMBus data input/output LED4 5 12 CP2 LED4 LED segment 4 SMBC SMBus clock LED5 6 11 SB LED5 LED segment 5 REF Voltage reference output CP1 7 10 DISP CP1 Control pin 1 VOUT EEPROM supply output VSS 8 9 VSS System ground SR 16-Pin Narrow SOIC PN294501.eps 6/99 C 1 bq2945 DISP Pin Descriptions VCC Supply voltage input LED1– LED5 LED display segment outputs DISP high disables the LED display. DISP floating allows the LED display to be active during charge if the rate is greater than 100mA. DISP low activates the display for 4 seconds. Each output may drive an external LED. ESCL SB Serial memory clock Serial memory data and address Bidirectional pin used to transfer address and data to and from the bq2945 and the external nonvolitile configuration memory. CP1– CP2 SMBD SMBC These open-drain outputs can be controlled by an SMBus command from the host. CP2 can also act as a digital input. Ground SR Sense resistor input SMBus data Open-drain bidirectional pin used to transfer address and data to and from the bq2945. Control pins 1 and 2 VSS Secondary battery input Monitors the pack voltage through a highimpedance resistor divider network. The pack voltage is reported in the SBD register function Voltage (0x09) and is monitored for end-of-discharge voltage and charging voltage parameters. Output used to clock the data transfer between the bq2945 and the external nonvolatile configuration memory. ESDA Display control input SMBus clock Open-drain bidirectional pin used to clock the data transfer to and from the bq2945. REF Reference output for regulator REF provides a reference output for an optional FET-based micro-regulator. The voltage drop (VSR) across pins SR and VSS is monitored and integrated over time to interpret charge and discharge activity. The SR input is connected to the sense resistor and the negative terminal of the battery. VSR < VSS indicates discharge, and VSR > VSS indicates charge. The effective voltage drop, VSRO, as seen by the bq2945 is VSR + VOS. (See Table 3.) VOUT Supply output Supplies power to the external EEPROM configuration memory. 2 bq2945 Figure 1 shows a typical battery pack application of the bq2945 using the LED capacity display, the serial port, and an external EEPROM for battery pack programming information. The bq2945 must be configured and calibrated for the battery-specific information to ensure proper operation. Table 1 outlines the configuration information that must be programmed in the EEROM. Functional Description General Operation The bq2945 determines battery capacity by monitoring the amount of charge put into or removed from a rechargeable battery. The bq2945 measures discharge and charge currents, estimates self-discharge, and monitors the battery for low-battery voltage thresholds. The charge is measured by monitoring the voltage across a small-value series sense resistor between the battery's negative terminal and ground. The available battery charge is determined by monitoring this voltage over time and correcting the measurement for the environmental and operating conditions. An internal temperature sensor eliminates the need for an external thermistor—reducing cost and components. An internal, temperature-compensated timebase eliminates the need for an external resonator, further reducing cost and components. The entire circuit in Figure 1 can occupy less than 3 4 square inch of board space. Chart 1 R4, R5, and R11 values depend on the battery voltage. R12 and R13 nominal values must be 10k NiMH Notes: Li-Ion See Chart 1 for resistor values and Q1 FET selection No. of Cells Q1 R4 R5 R11 2 BSS138 100K 301K 604K 3 BSS138 100K 499K 806K 4 2N7002 100K 698K 604K 6 BSS138 100K 499K 499K 8 BSS138 100K 698K 806K 9 2N7002 100K 806K 499K 10 2N7002 100K 909K 604K 12 2N7002 86.5K 909K 909K Figure 1. Battery Pack Application Diagram—LED Display 3 bq2945 Table 1. Configuration Memory Map Parameter Name Address Description EEPROM length 0x00 Number of EEPROM data locations must = 0x64 EEPROM check1 0x01 EEPROM data integrity check byte must = 0x5b Length Units 8 bits NA 8 bits NA Remaining time alarm 0x02/0x03 Sets RemainingTimeAlarm (0x02) 16 bits minutes Remaining capacity alarm 0x04/0x05 Sets RemainingCapacityAlarm (0x01) 16 bits mAh Reserved 0x06/0x07 Reserved for future use 16 bits NA Initial charging current 0x08/0x09 Sets the initial charging current 16 bits mA Charging voltage 0x0a/0x0b Sets ChargingVoltage (0x15) 16 bits mV Battery status 0x0c/0x0d Initializes BatteryStatus (0x16) 16 bits NA Cycle count 0x0e/0x0f Initializes and stores CycleCount (0x17) 16 bits cycles Design capacity 0x10/0x11 Sets DesignCapacity (0x18) 16 bits mAh Design voltage 0x12/0x13 Sets DesignVoltage (0x19) 16 bits mV Specification information 0x14/0x15 Programs SpecificationInfo (0x1a) 16 bits NA Manufacturer date 0x16/0x17 Programs ManufactureDate (0x1b) 16 bits NA Serial number 0x18/0x19 Programs SerialNumber (0x1c) 16 bits NA Fast-charging current 0x1a/0x1b Sets ChargingCurrent (0x14) 16 bits mA Maintenance-charge current 0x1c/0x1d Sets the trickle current request 16 bits mA Reserved 0x1e/0x1f Reserved must = 0x0000 16 bits mAh Manufacturer name 0x20-0x2b Programs ManufacturerName (0x20) 96 bits NA Current integration gain 0x2c/0x2d Programs the sense resistor scale 16 bits NA Reserved 0x2e/0x2f Reserved for future use 16 bits NA Device name 0x30-0x37 Programs DeviceName (0x21) 64 bits NA Li-Ion taper current 0x38/0x39 16 bits mA Maximum overcharge limit 0x3a/0x3b Sets the maximum amount of overcharge 16 bits NA Sets the upper limit of the taper current for charge termination Reserved 0x3c Reserved must = 0x00 8 bits NA Access protect 0x3d Locks commands outside of the SBS data set 8 bits NA FLAGS1 0x3e Initializes FLAGS1 8 bits NA FLAGS2 0x3f Initializes FLAGS2 8 bits NA Device chemistry 64 bits NA Battery voltage offset 0x48 Voltage calibration value 8 bits NA Temperature offset 0x49 Temperature calibration value 8 bits NA 0x4a Sets the maximum charge temperature and the ∆T step for ∆T/∆t termination 8 bits NA Maximum temperature and ∆T step 0x40-0x47 Programs DeviceChemistry (0x22) 4 bq2945 Table 1. Configuration Memory Map (Continued) Length Units Charge efficiency Parameter Name Address 0x4b Sets the high/low charge rate efficiencies Description 8 bits NA Full-charge percentage 0x4c Sets the percent at which the battery is considered fully charged 8 bits NA Digitial filter 0x4d Sets the minimum charge/discharge threshold 8 bits NA Reserved 0x4e Reserved for future use 8 bits NA Self-discharge rate 0x4f Sets the battery’s self-discharge rate 8 bits NA Manufacturer data 0x50-0x55 Programs ManufacturerData (0x23) 48 bits NA Voltage gain1 0x56/0x57 Battery divider calibration value 16 bits NA Reserved 0x58-0x59 Reserved 16 bits NA Current measurement gain 0x5a/0x5b Sense resistor calibration value 16 bits NA End of discharge voltage1 0x5c/0x5d Sets EDV1 16 bits NA End of discharge voltage final 0x5e/0x5f Sets EDVF 16 bits NA Full-charge capacity 0x60/0x61 Initializes and stores FullChargeCapacity (0x10) 16 bits mAh ∆t step 0x62 Sets the ∆t step for ∆T/∆t termination 8 bits NA Hold-off time 0x63 Sets ∆T/∆t hold-off timer 8 bits NA EEPROM check 2 0x64 EEPROM data integrity check byte must = 0xb5 8 bits NA Reserved 0x65-0x7f Reserved for future use 5 NA bq2945 Voltage Thresholds Layout Considerations In conjunction with monitoring VSR for charge/discharge currents, the bq2945 monitors the battery potential through the SB pin. The voltage potential is determined through a resistor-divider network per the following equation: The bq2945 measures the voltage differential between the SR and VSS pins. VOS (the offset voltage at the SR pin) is greatly affected by PC board layout. For optimal results, the PC board layout should follow the strict rule of a single-point ground return. Sharing high-current ground with small signal ground causes undesirable noise on the small signal nodes. Additionally, in reference to Figure 1: R5 MBV = − 1 R4 2.25 where MBV is the maximum battery voltage, R5 is connected to the positive battery terminal, and R4 is connected to the negative battery terminal. R5/R4 should be rounded to the next higher integer. R5 and R4 should be sized so that the voltage at the SB pin (VSB) should never exceed 2.4V. n n The battery voltage is monitored for the end-ofdischarge voltages (EDV1 and EDVF) and for alarm warning conditions. EDV threshold levels are used to determine when the battery has reached an “empty” state. The bq2945 generates an alarm warning when the battery voltage exceeds the maximum charging voltage by 5% or if the voltage is below EDVF. The battery voltage gain, the two EDV thresholds, and the charging voltage are programmable in the EEPROM. n n The capacitors (C1 and C2) should be placed as close as possible to the SB and VCC pins, and their paths to VSS should be as short as possible. A high-quality ceramic capacitor of 0.1µf is recommended for VCC. The sense resistor capacitor (C3) should be placed as close as possible to the SR pin. The bq2945 should be in thermal contact with the cells for optimum temperature measurement. An optional zener (D9) may be necessary to ensure that VCC is not above the maximum rating during operation. Gas Gauge Operation If VSB is below either of the two EDV thresholds, the associated flag is latched and remains latched, independent of VSB, until the next valid charge. The operational overview diagram in Figure 2 illustrates the operation of the bq2945. The bq2945 accumulates a measure of charge and discharge currents, as well as an estimation of self-discharge. Charge currents are compensated for temperature and state-of-charge of the battery. Self-discharge is temperature-compensated. EDV monitoring may be disabled under certain conditions. If the discharge current is greater than approximately 6A, EDV monitoring is disabled and resumes after the current falls below 6A. The main counter, RemainingCapacity (RM), represents the available battery capacity at any given time. Battery charging increments the RM register, whereas battery discharging and self-discharge decrement the RM register and increment the internal Discharge Count Register (DCR). Reset The bq2945 is reset when first connected to the battery pack. On power-up, the bq2945 initializes and reads the EEPROM configuration memory. The bq2945 can also be reset with a command over the SMBus. The software reset sequence is the following: (1) write MaxError (0x0c) to 0x0000; (2) write the reset register (0x64) to 0x8009. A software reset can only be performed if the bq2945 is in an unlocked state as defined by the value in location 0x3d of the EEPROM (EE 0x3d) on power-up. The Discharge Count Register is used to update the FullChargeCapacity (FCC) register only if a complete battery discharge from full to empty occurs without any partial battery charges. Therefore, the bq2945 adapts its capacity determination based on the actual conditions of discharge. Temperature The battery's initial full capacity is set to the value stored in EE 0x60-0x61. Until FCC is updated, RM counts up to, but not beyond, this threshold during subsequent charges. The bq2945 monitors temperature sensing using an internal sensor. The temperature is used to adapt charge and self-discharge compensations as well as to monitor for maximum temperature and ∆T/∆t during a bq2945 controlled charge. Temperature may also be accessed over the SMBus with command 0x08. 1. FullChargeCapacity or learned-battery capacity: FCC is the last measured discharge capacity of the battery. On initialization (application of VCC or reset), FCC is set to the value stored in the EEPROM. During subsequent discharges, FCC is updated with the 6 bq2945 Charge Current Inputs Discharge Current Self-Discharge Timer State-of-charge and Temperature Compensation Temperature Compensation Main Counters and Capacity Reference (FCC) + - + Remaining Capacity (RM) < Full Charge Capacity (FCC) + Discharge Count Qualified Register Transfer (DCR) Temperature, Other Data Chip-Controlled Two-Wire Available Charge Serial Interface LED Display Outputs FG294501.eps Figure 2. Operational Overview both discharge and self-discharge increment the DCR. After RM = 0, only discharge increments the DCR. The DCR resets to 0 when RM = FCC. The DCR does not roll over but stops counting when it reaches FFFFh. latest measured capacity in the Discharge Count Register, representing a discharge from full to below EDV1. A qualified discharge is necessary for a capacity transfer from the DCR to the FCC register. Once updated, the bq2945 writes the new FCC to the EEPROM. The FCC also serves as the 100% reference threshold used by the relative state-of-charge calculation and display. 2. The DCR value becomes the new FCC value on the first charge after a qualified discharge to EDV1. A qualified discharge to EDV1 occurs if all of the following conditions exist: DesignCapacity (DC): The DC is the user-specified battery capacity and is programmed from external EEPROM. The DC also provides the 100% reference for the absolute display mode. 3. n RemainingCapacity (RM): n RM counts up during charge to a maximum value of FCC and down during discharge and self-discharge to 0. RM is set to 000Ah after the EDV1 threshold has been reached and a valid charge has been detected. To prevent overstatement of charge during periods of overcharge, RM stops incrementing when RM = FCC. RM may optionally be written to a userdefined value when fully charged if the battery pack is under bq2945 charge control. On initialization, RM is set to the value stored in EE 0x1e—0x1f. 4. n No valid charge initiations (charges greater than 10mAh), where VSRO > +VSRD occurred during the period between RM = FCC and EDV1 detected. The self-discharge count is not more than 256mAh. The temperature is ≥ 273°K (0°C) when the EDV1 level is reached during discharge. The valid discharge flag (VDQ) in FLAGS1 indicates whether the present discharge is valid for an FCC update. FCC cannot be reduced by more than 256mAh during any single cycle. Charge Counting Charge activity is detected based on a positive voltage on the SR input. If charge activity is detected, the bq2945 increments RM at a rate proportional to VSRO and, if enabled, activates an LED display. Charge actions increment the RM after compensation for charge state and temperature. Discharge Count Register (DCR): The DCR counts up during discharge independent of RM and can continue increasing after RM has decremented to 0. Prior to RM = 0 (empty battery), 7 bq2945 The bq2945 determines charge activity sustained at a continuous rate equivalent to VSRO > +VSRD. A valid charge equates to sustained charge activity greater than 10 mAh. Once a valid charge is detected, charge threshold counting continues until VSRO falls below VSRD. VSRD is a programmable threshold as described in the Digital Magnitude Filter section. seconds–320seconds). Typical settings for 1°C/min include 2°C over 120 seconds and 3°C over 180 seconds. Longer times are required for increased slope resolution. ∆T ∆T is set by the formula: = ∆t ∆t [(lower nibble of EE 0x4a)∗ 2 + 16 ] / 10 [2' s(EE 0x62) ∗ 20] Discharge Counting oC s In addition to the ∆T/∆t timer, there is a hold-off timer, which starts when the battery is being charged at more than 255mA and the temperature is above 25°C. Until this timer expires, ∆T/∆t is suspended. If the temperature falls below 25°C, or if charging current falls below 255mA, the timer is reset and restarts only if these conditions are once again within range. The hold-off time is programmed in EE 0x63. All discharge counts where VSRO < -VSRD cause the RM register to decrement and the DCR to increment. VSRD is a programmable threshold as described in the Digital Magnitude Filter section. Self-Discharge Estimation The bq2945 continuously decrements RM and increments DCR for self-discharge based on time and temperature. The bq2945 self-discharge estimation rate is programmed in EE 0x4f and can be set from 0 to 25% per day for 20–30°C. This rate doubles every 10°C from 30°C to 70°C and halves every 10°C from 20°C to 0°C. Charge Termination Once the bq2945 detects a valid charge termination, the Fully_Charged, Terminate_Charge_Alarm, and the Over_Charged_Alarm bits are set in BatteryStatus, and the requested charge current is set to zero. Once the terminating conditions cease, the Terminate_Charge_Alarm and the Over_Charged_Alarm are cleared, and the requested charging current is set to the maintenance rate. The bq2945 requests the maintenance rate until RM falls below 95% of full-charge percentage. Once this occurs, the Fully_Charged bit is cleared, and the requested charge current and voltage are set to the fast-charge rate. Charge Control The bq2945 supports SBS charge control by broadcasting the ChargingCurrent and the ChargingVoltage to the Smart Charger address. The bq2945 broadcasts charging commands every 10 seconds; the broadcasts can be disabled by writing bit 14 of BatteryMode to 1. On reset, the initial charging current broadcast to the charger is set to the value programmed in EE 0x080x09. The bq2945 updates the value used in the charging current broadcasts based on the battery’s state of charge, voltage, and temperature. Bit 4 (CC) in FLAGS2 determines whether RM is modified after a ∆T/∆t or current taper termination occurs. If CC = 1, RM may be set from 0 to 100% of the FullChargeCapacity as defined in EE 0x4c. If RM is below the full-charge percentage, RM is set to the full-charge percentage of FCC. If RM is above the full-charge percentage, RM is not modified. The bq2945 internal charge control is compatible with nickel-based and Li-Ion chemistries. The bq2945 uses current taper detection for Li-Ion primary charge termination and ∆T/∆t for nickel based primary charge termination. The bq2945 also provides a number of safety terminations based on battery capacity, voltage, and temperature. Charge Suspension The bq2945 may temporarily suspend charge if it detects a charging fault. The charging faults include the following conditions: Current Taper n For Li-Ion charge control, the ChargingVoltage must be set to the desired pack voltage during the constant voltage charge phase. The bq2945 detects a current taper termination when it measures the pack voltage to be within 128mV of the requested charging voltage and when the AverageCurrent is between the programmed threshold in EE 0x38—0x39 and 100 mA for at least 40s. n ∆T/∆t The ∆T/∆t used by the bq2945 is programmable in both the temperature step (1.6°C–4.6°C) and time step (20 8 Maximum Overcharge: If charging continues for more than the programmed maximum overcharge limit as defined in EE 0x3a—0x36 beyond RM=FCC, the Fully_Charged bit is set, and the requested charging current is set to the maintenance rate. Overvoltage: An over-voltage fault exists when the bq2945 measures a voltage more than 5% above the ChargingVoltage. When the bq2945 detects an overvoltage 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 bq2945 the current drops below 256mA and the voltage is less than 105% of ChargingVoltage. n n n n Q ET = 0 if T < 30°C Q ET = 0.02 if 30 ° C ≤ T < 40 ° C 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. Q ET = 0.05 if T ≥ 40 ° C QET is 0 over the entire temperature range for Li-Ion. Digital Magnitude Filter The bq2945 has a programmable digital filter to eliminate charge and discharge counting below a set threshold, VSRD. Table 2 shows typical digital filter settings. The proper digital filter setting can be calculated using the following equation. 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. DMF = 45 VSRD Table 2. Typical Digital Filter Settings 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. 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. 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 Error Summary Count Compensations Capacity Inaccurate Charge activity is compensated for temperature and state-of-charge before updating the RM and/or DCR. Self-discharge estimation is compensated for temperature before updating RM or DCR. 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 capacity. 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 adjusted to account for changes in actual battery capacity. Periodic qualified discharges from full to empty will minimize errors in FCC. Charge Compensation Charge efficiency is compensated for state-of-charge, temperature, and battery chemistry. The charge efficiency is adjusted using the following equations: 1.) RM = RM * (Q EFC − Q ET ) Current-Sensing Error where RelativeStateOfCharge < FullChargePercentage, and Q EFC is the programmed fast-charge efficiency varying from 0.75 to 1.0. 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. 2.) RM = RM * (Q ETC − Q ET ) Display where RelativeStateOfCharge ≥ FullChargePercentage and Q ETC is the programmed maintenance (trickle) charge efficiency varying from 0.75 to 1.0. 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 relative mode, the battery charge is represented as a percentage of the FCC. Each LED segment represents 20% of the FCC. Q ET is used to adjust the charge efficiency as the battery temperature increases according to the following: 9 bq2945 Table 3. bq2945 Current-Sensing Errors Typical Maximum Units VOS Symbol Offset referred to VSR Parameter ± 75 ± 150 µV INL Integrated non-linearity error ±1 ±4 % Add 0.1% per °C above or below 25°C and 1% per volt above or below 4.25V. INR Integrated nonrepeatability error ± 0.5 ±1 % Measurement repeatability given similar operating conditions. In absolute mode, each segment represents a fixed amount of charge, 20% of the DesignCapacity. As the battery wears out over time, it is possible for the FCC to be below the design capacity. In this case, all of the LEDs may not turn on in absolute mode, representing the reduction in the actual battery capacity. Notes DISP = VCC. Communicating with the bq2945 The bq2945 includes a simple two-pin (SMBC and SMBD) bi-directional serial data interface. A host processor uses the interface to access various bq2945 registers; see Table 4. This method allows battery characteristics to be monitored easily. The open-drain SMBD and SMBC pins on the bq2945 are pulled up by the host system, or may be connected to VSS, if the serial interface is not used. When DISP is tied to VCC, the LED1-5 outputs are inactive. When DISP is left floating, the display becomes active whenever the bq2945 detects a charge rate of 100mA or more. When pulled low, the segment outputs become active immediately for a period of approximately 4 seconds. The DISP pin must be returned to float or VCC to reactivate the display. The interface uses a command-based protocol, where the host processor sends the battery address and an eightbit command byte to the bq2945. The command directs the bq2945 to either store the next data received to a register specified by the command byte or output the data specified by the command byte. LED1 blinks at a 4Hz rate whenever VSB has been detected to be below EDV1 (EDV1 = 1), indicating a lowbattery condition. VSB below EDVF (EDVF = 1) disables the display output. bq2945 Data Protocols Microregulator The host system, acting in the role of a Bus master, uses the read word and write word protocols to communicate integer data with the bq2945. (See Figure 3.) The bq2945 can operate directly from three nickel chemistry cells. To facilitate the power supply requirements of the bq2945, an REF output is provided to regulate an external low-threshold n-FET. A micropower source for the bq2945 can be inexpensively built using a 2N7002 or BSS138 FET and an external resistor. (See Figure 1.) The value of R11 depends on the battery pack’s nominal voltage. Host-to-bq2945 Message Protocol The Bus Host communicates with the bq2945 using one of three protocols: n Read word n Write word n Read block The particular protocol used is a function of the command. The protocols used are shown in Figure 3. Host-to-bq2945 Messages (see Table 4) ManufacturerAccess() (0x00) This function is used to control CP1 and CP2. (See Table 7.) 10 bq2945 1 S 7 Battery Address 0001011 1 1 8 1 8 1 8 1 1 0 A Command Code A Data byte low A Data byte high A P Write Word 1 S 7 Battery Address 0001011 1 1 8 1 1 7 1 1 0 A Command Code A S Battery Address 1 A 8 1 8 1 Data byte low A Data byte high A P System Host Read Word 1 S 7 Battery Address 0001011 1 1 8 1 1 7 1 1 0 A Command Code A S Battery Address 1 A bq2945 8 1 8 1 8 1 8 1 1 Byte Count =N A Data byte 1 A Data byte 2 A Data byte N A P Block Read A – ACKNOWLEDGE A – NOT ACKNOWLEDGE S – START P – STOP FG294501.eps Figure 3. Host Communication Protocols RemainingCapacityAlarm() (0x01) BatteryMode() (0x03) This function sets or returns the low-capacity alarm value. When RM falls below the RemainingCapacityAlarm value initialized from the external EEPROM, the Remaining_Capacity_Alarm bit is set in BatteryStatus. The system may alter this alarm during operation. This read/write word selects the various battery operational modes. The bq2945 supports the battery capacity information specified in mAh. This function also determines whether the bq2945 charging values are broadcasted to the Smart Battery Charger address. Writing bit 14 to 1 disables voltage and current Master Mode broadcasts to the Smart Battery Charger. Bit 14 is automatically reset to 0 if SMBC and SMBD = 0 for greater than 2 seconds (i.e. pack removal). Input/Output: unsigned integer. This sets/returns the value where the Remaining_Capacity_Alarm bit is set in Battery Status. Units: mAh Writing bit 13 to 1 disables all Master Mode broadcasts including alarm messages to the Smart Battery Charger and Host. The bit remains set until overwritten. Programming bit 3 of FLAGS2 in the EEPROM (EE0x3f) initializes this bit to a 1. Range: 0 to 65,535mAh RemainingTimeAlarm() (0x02) This function sets or returns the low remaining time alarm value. When the AverageTimeToEmpty falls below this value, the Remaining_Time_Alarm bit in BatteryStatus is set. The default value for this register is programmed in EE 0x02-0x03. The system may alter this alarm during operation. Bit 7 is the condition request flag. It is set when the bq2945 is initialized from the EEPROM and reset when a learning cycle has been completed. It is also set to a 1 if CycleCount increases by 32 without a new learning cycle. AtRate() (0x04) Input/Output: unsigned integer. This sets/returns the value where the Remaining_Time_Alarm bit is set in Battery Status. This read/write word is the first half of a two-function set used to set the AtRate value used in calculations made by the AtRateTimeToFull and AtRateTimeToEmpty. Units: minutes Range: 0 to 65,535 minutes n 11 When the AtRate value is positive, the AtRateTimeToFull function returns the predicted time to full-charge at the AtRate value of charge. bq2945 Table 4. bq2945 Register Functions Function Code Access Units Defaults1 ManufacturerAccess 0x00 read/write - - Remaning_Capacity_Alarm 0x01 read/write mAh E2 Remaining_Time_Alarm 0x02 read/write minutes E2 BatteryMode 0x03 read/write bit flag - AtRate 0x04 read/write mA - AtRateTimeToFull 0x05 read minutes - AtRateTimeToEmpty 0x06 read minutes - AtRateOK 0x07 read Boolean - Temperature 0x08 read 0.1°K 2930 Voltage 0x09 read mV E2 Current 0x0a read mA 0 AverageCurrent 0x0b read mA 0 MaxError 0x0c read percent 100 RelativeStateOfCharge 0x0d read percent - AbsoluteStateOfCharge 0x0e read percent - RemainingCapacity 0x0f read mAh E2 FullChargeCapacity 0x10 read mAh E2 RunTimeToEmpty 0x11 read minutes - AverageTimeToEmpty 0x12 read minutes - AverageTimeToFull 0x13 read minutes - ChargingCurrent 0x14 read mA E2 ChargingVoltage 0x15 read mV E2 Battery Status 0x16 read bit flags E2 CycleCount 0x17 read cycle E2 DesignCapacity 0x18 read mAh E2 DesignVoltage 0x19 read mV E2 Specification Info 0x1a read - E2 ManufactureDate 0x1b read - E2 SerialNumber 0x1c read integer E2 0x1d - 0x1f - - - ManufacturerName 0x20 read string E2 DeviceName 0x21 read string E2 Reserved Note: 1. Defaults after reset or power-up. 12 bq2945 Table 4. bq2945 Register Functions (Continued) Code Access Units Defaults1 DeviceChemistry 0x22 read string E2 ManufacturerData 0x23 read string E2 FLAG1 and FLAG2 0x2f read bit flags E2 End of Discharge Voltage 1 (EDV1) 0x3e read - E2 End of Discharge Voltage Final (EDVF) 0x3f read - E2 Function Note: 1. Defaults after reset or power-up. 13 bq2945 n When the AtRate value is negative, the AtRateTimeToEmpty function returns the predicted operating time at the AtRate value of discharge. Output: unsigned integer. Returns the cell temperature in tenths of degrees Kelvin increments. Units: 0.1°K Input/Output: signed integer. AtRate is positive for charge and negative for discharge. Range: 0 to +500.0°K Units: mA Granularity: 0.5°K or better Range: -32,768mA to 32,767mA Accuracy: ± 3°K after calibration AtRateTimeToFull() (0x05) Voltage() (0x09) This read-only word returns the predicted remaining time to fully charge the battery at the AtRate value (mA) and is valid only if read immediately after an AtRate command. This read-only word returns the cell-pack voltage (mV). Output: unsigned integer. Returns the battery terminal voltage in mV. Units: mV Output: unsigned integer. Returns the predicted time to full charge. Range: 0 to 65,535mV Units: minutes Granularity: 0.2% of DesignVoltage Range: 0 to 65,534min Accuracy: ± 1% of DesignVoltage after calibration Granularity: 2 min or better Current() (0x0a) Invalid Data Indication: 65,535 indicates that the AtRate value is negative. This read-only word returns the current through the battery's terminals (mA). AtRateTimeToEmpty() (0x06) Output: signed integer. Returns the charge/discharge rate in mA, where positive is for charge and negative is for discharge This read-only word returns the predicted remaining operating time if the battery is discharged at the AtRate value and is valid only if read immediately after an AtRate command. Units: mA Range: 0 to 32,767mA for charge or 0 to –32,768mA for discharge Output: unsigned integer. Returns the predicted time to empty. Granularity: 0.2% of the DesignCapacity or better Units: minutes Accuracy: ± 1% of the DesignCapacity after calibration Range: 0 to 65,534min AverageCurrent() (0x0b) Granularity: 2min or better This read-only word returns a rolling average of the current through the battery's terminals. The AverageCurrent function returns meaningful values after the battery's first minute of operation. Invalid Data Indication: 65,535 indicates that the AtRate value is not negative. AtRateOK() (0x07) Output: signed integer. Returns the charge/discharge rate in mA, where positive is for charge and negative is for discharge This read-only word returns a Boolean value that indicates whether or not the EDVF flag has been set. Boolean: Indicates if the battery can supply additional energy. Units: mA Units: Boolean Range: 0 to 32,767mA for charge or 0 to –32,768mA for discharge Range: TRUE ≠ 0, FALSE = 0 Granularity: 0.2% of the DesignCapacity or better Accuracy: ± 1% of the DesignCapacity after calibration Temperature() (0x08) This read-only word returns the cell-pack's internal temperature. 14 bq2945 MaxError() (0x0c) Granularity: 0.2% of DesignCapacity or better Returns the expected margin of error (%) in the state of charge calculation. Accuracy: ±MaxError ∗ FCC after circuit and capacity calibration Output: unsigned integer. Returns the percent uncertainty for selected information. FullChargeCapacity() (0x10) This read-only word returns the predicted pack capacity when it is fully charged. FullChargeCapacity defaults to the value programmed in the external EEPROM until a new pack capacity is learned. The new FCC is stored to EEPROM within 400ms of a valid charge after a qualified discharge. Units: % Range: 0 to 100% RelativeStateOfCharge() (0x0d) This read-only word returns the predicted remaining battery capacity expressed as a percentage of FullChargeCapacity (%). RelativeStateOfCharge is only valid for battery capacities more than 1504mAh and less than 10,400mAh. Output: unsigned integer. Returns the estimated full charge capacity in mAh. Units: mAh Output: unsigned integer. Returns the percent of remaining capacity. Range: 0 to 65,535mAh Units: % Accuracy: ±MaxError ∗ FCC after circuit and capacity calibration Granularity: 0.2% of DesignCapacity or better Range: 0 to 100% Granularity: 1% RunTimeToEmpty() (0x11) Accuracy: ±MaxError after circuit and capacity calibration This read-only word returns the predicted remaining battery life at the present rate of discharge (minutes). The RunTimeToEmpty value is calculated based on Current. AbsoluteStateOfCharge() (0x0e) This read-only word returns the predicted remaining battery capacity expressed as a percentage of DesignCapacity (%). Note that AbsoluteStateOfCharge can return values greater than 100%. Absolute StateOfCharge is only valid for battery capacities more than 1504mAh and less than 10,400mAh. Output: unsigned integer. Returns the minutes of operation left. Units: minutes Range: 0 to 65,534min Granularity: 2min or better Output: unsigned integer. Returns the percent of remaining capacity. Invalid data indication: 65,535 indicates battery is not being discharged. Units: % Range: 0 to 65,535% AverageTimeToEmpty() (0x12) Granularity: 1% This read-only word returns the predicted remaining battery life at the present average discharge rate (minutes). The AverageTimeToEmpty is calculated based on AverageCurrent. Accuracy: ±MaxError after circuit and capacity calibration RemainingCapacity() (0x0f) Output: unsigned integer. Returns the minutes of operation left. This read-only word returns the predicted remaining battery capacity. The RemainingCapacity value is expressed in mAh. Units: minutes Range: 0 to 65,534min Output: unsigned integer. Returns the estimated remaining capacity in mAh. Granularity: 2min or better Units: mAh Invalid data indication: 65,535 indicates battery is not being discharged. Range: 0 to 65,535mAh 15 bq2945 Invalid data indication: 65,535 indicates that the Smart Charger should operate as a voltage source outside its maximum regulated current range. AverageTimeToFull() (0x13) This read-only word returns the predicted time until the Smart Battery reaches full charge at the present average charge rate (minutes). ChargingVoltage() (0x15) Output: unsigned integer. Returns the remaining time in minutes to full. If enabled, the bq2945 sends the desired voltage in mV to the Smart Battery Charger. Units: minutes Output: unsigned integer. Transmits/returns the charger voltage output in mV. Range: 0 to 65,534min Units: mV Granularity: 2min or better Range: 0 to 65,534mV Invalid data indication: 65,535 indicates battery is not being charged. Granularity: 0.2% of the DesignVoltage or better Invalid data indication: 65,535 indicates that the Smart Battery Charger should operate as a current source outside its maximum regulated voltage range. ChargingCurrent() (0x14) If enabled, the bq2945 sends the desired charging rate in mA to the Smart Battery Charger. Output: unsigned integer. Transmits/returns the maximum charger output current in mA. BatteryStatus() (0x16) This read-only word returns the battery status word. Units: mA Output: unsigned integer. Returns the status register with alarm conditions bitmapped as shown in Table 5. Range: 0 to 65,534mA Granularity: 0.2% of the design capacity or better Some of the BatteryStatus flags (Remaining_Capacity_Alarm and Remaining_Time_Alarm) are calculated based on current. See Table 8 and 9 for definitions. Table 5. Status Register CycleCount() (0x17) This read-only word returns the number of charge/discharge cycles the battery has experienced. A charge/discharge cycle starts from a base value equivalent to the battery's state-of-charge on completion of a charge cycle. The bq2945 increments the cycle counter during the current charge cycle if the battery has been discharged 15% below the state-of-charge at the end of the last charge cycle. This prevents false reporting of small charge/discharge cycles. The cycle count is stored in EEPROM within 400ms of an update. Alarm Bits 0x8000 Over_Charged_Alarm 0x4000 Terminate_Charge_Alarm 0x2000 Reserved 0x1000 Over_Temp_Alarm 0x0800 Terminate_Discharge_Alarm 0x0400 Reserved 0x0200 Remaining_Capacity_Alarm 0x0100 Remaining_Time_Alarm Output: unsigned integer. Returns the count of charge/discharge cycles the battery has experienced. Status Bits 0x0080 Initialized Units: cycles 0x0040 Discharging 0x0020 Fully_Charged Range: 0 to 65,535 cycles; 65,535 indicates battery has experienced 65,535 or more cycles. 0x0010 Fully_Discharged Granularity: 1 cycle Error Code 0x00000x000f DesignCapacity() (0x18) Reserved for error codes This read-only word returns the theoretical capacity of a new pack. The DesignCapacity value is expressed in mAh at the nominal discharge rate. 16 bq2945 Table 6. Bit Descriptions for FLAGS1 and FLAGS2 (MSB) 7 FLAGS2 DMODE FLAGS1 6 5 4 3 2 1 0 (LSB) CP2 DI CHM CC - OV LTF OC - VQ - VDQ SEDV EDV1 EDVF - Note: - = Reserved Output: unsigned integer. Returns the battery capacity in mAh. ManufacturerName() (0x20) This read-only string returns a character string where the first byte is the number of characters available. The maximum number of characters is 11. The character string contains the battery manufacturer's name. For example, “Unitrode” identifies the battery pack manufacturer as Unitrode. Units: mAh Range: 0 to 65,535mAh DesignVoltage() (0x19) This read-only word returns the theoretical voltage of a new pack in mV. Output: string or ASCII character string DeviceName() (0x21) Output: unsigned integer. Returns the battery's normal terminal voltage in mV. This read-only string returns a character string where the first byte is the number of characters available. The maximum number of characters is 7. The 7-byte character string contains the battery's name. For example, a DeviceName of “bq2945” indicates that the battery is a model bq2945. Units: mV Range: 0 to 65,535mV Specification Info() (0x1a) Output: string or ASCII character string This read-only word returns the specification revision the bq2945 supports. DeviceChemistry() (0x22) ManufactureDate() (0x1b) This read-only string returns a character string where the first byte is the number of characters available. The maximum number of characters is 5. The 5-byte character string contains the battery's chemistry. For example, if the DeviceChemistry function returns “NiMH,” the battery pack contains nickel-metal hydride cells. This read-only word returns the date the cell was manufactured in a packed integer word. The date is packed as follows: (year - 1980) ∗ 512 + month ∗ 32 + day. Field Bits Used Day Month Year Output: string or ASCII character string Format Allowable Value 0–4 5-bit binary value 1–31 (corresponds to date) 5–8 4-bit binary value 1–12 (corresponds to month number) 9–15 7-bit binary value 0 * 127 (corresponds to year biased by 1980) ManufacturerData() (0x23) This read-only string allows access to an up to 5-byte manufacturer data string. Output: block data—data whose meaning is assigned by the Smart Battery's manufacturer. End of Discharge Voltage1 (0x3e) This read-only word returns the first end-of-discharge voltage programmed for the pack. SerialNumber() (0x1c) This read-only word returns a serial number. This number, when combined with the ManufacturerName, the DeviceName, and the ManufactureDate, uniquely identifies the battery. Output: two’s complemented unsigned integer. Returns battery end-of-discharge voltage programmed in EEPROM in mV. Output: unsigned integer 17 bq2945 Bit 4, the Charge Control flag (CC), determines whether a bq2945-based charge termination will set RM to a user-defined programmable full charge capacity. End of Discharge VoltageF (0x3f) This read-only word returns the final end-of-discharge voltage programmed for the pack. The CC values are: Output: two’s complemented unsigned integer. Returns battery final end-of-discharge voltage programmed in EEPROM in mV. 7 - FLAGS1&2() (0x2f) This read-only register returns an unsigned integer representing the internal status registers of the bq2945. The MSB represents FLAGS2, and the LSB represents FLAGS1. See Table 6 for the bit description for FLAGS1 and FLAGS2. The Display Mode flag (DMODE), bit 7 determines whether the bq2945 displays Relative or Absolute capacity. 5 - FLAGS2 Bits 4 3 - 2 - 1 - 1 Selects Relative display 7 - 6 CP2DI RM is not modified on valid bq2945 charge termination 1 RM is set to a programmable percentage of the FCC when a valid bq2945 charge termination occurs 2 - 1 - 0 - 6 - Selects Nickel 1 Selects Li-Ion FLAGS2 Bits 4 3 - 2 OV 1 - 0 - 0 Voltage < 1.05 ∗ ChargingVoltage 1 Voltage ≥ 1.05 ∗ ChargingVoltage The LTF values are: 7 2 - 1 - 0 - 6 - 5 - FLAGS2 Bits 4 3 - 2 - 1 LTF 0 - Where LTF is: Where CHM is: 0 5 - Bit 1, the Low Temperature Fault flag (LTF), is set when temperature < 0°C and cleared when temperature > 5°C. The CHM values are: 7 - 6 - Where OV is: The Chemistry flag (CHM), bit 5, selects Li-Ion or nickel compensation factors. FLAGS2 Bits 5 4 3 CHM - 0 - The OV values are: 0 - Bit 6 reflects the high/low state of CP2. FLAGS2 Bits 5 4 3 - 1 - Bit 2, the Overvoltage flag (OV), is set when the bq2945 detects a pack voltage 5% greater than the programmed charging voltage. This bit is cleared when the pack voltage falls 5% below the programmed charging voltage. Where DMODE is: Selects Absolute display 2 - 0 7 - 0 FLAGS2 Bits 4 3 CC - Bit 3 is reserved. The DMODE values are: 6 - 5 - Where CC is: FLAGS2 7 DMODE 6 - 0 Temperature > 5°C 1 Temperature < 0°C Bit 0, the Overcurrent flag (OC), is set when the average current is 25% greater than the programmed charging current. If the charging current is programmed less than 1024mA, overcurrent is set if the average current is 256mA greater than the programmed charging current. 18 bq2945 This flag is cleared when the average current falls below 256mA. The OC values are: 7 - 6 - 5 - FLAGS2 Bits 4 3 2 - 1 - 1 On first discharge after RM=FCC The SEDV values are: 0 AverageCurrent is less than 1.25 ∗ ChargingCurrent or less than 256mA if charging current is programmed less than 1024mA 1 AverageCurrent exceeds 1.25 ∗ ChargingCurrent or 256mA if the charging current is programmed less than 1024mA. This bit is cleared if average current < 256mA. 7 - The Valid Charge flag (VQ), bit 5, is set when VSRO ≥ |VSRD| and 10mAh of charge has accumulated. This bit is cleared during a discharge and when VSRO ≤ |VSRD|. 2 - 1 - Current < 6.15A 1 Current > 6.15A 6 - 5 - V SRO ≤ |V SRD| 1 V SRO ≥ |V SRD| and 10mAh of charge has accumulated 0 VQ = 1 and Voltage > EDV1 1 Voltage < EDV1 and SEDV = 0 1 EDV1 0 - The EDVF values are: Bit 4 is reserved. 7 - The Valid Discharge flag (VDQ), bit 3, is set when a valid discharge is occurring (discharge cycle valid for learning new full charge capacity) and cleared if a partial charge is detected, EDV1 is asserted when T < 0°C, or self-discharge accounts for more than 256mAh of the discharge. 2 - 1 - 6 - 5 - FLAGS1 Bits 4 3 2 - 1 - 0 EDVF Where EDVF is: The VDQ values are: FLAGS1 Bits 4 3 VDQ FLAGS1 Bits 4 3 2 - The Final End-of-Discharge Voltage flag (EDVF), bit 0, is set when Voltage < EDVF and SEDV = 0 and cleared when VQ = 1 and Voltage > EDVF. 0 5 - 0 - Where EDV1 is: 0 - Where VQ is: 6 - 1 - The EDV1 values are: The VQ values are: 7 - FLAGS1 Bits 4 3 2 SEDV 0 7 FLAGS1 Bits 4 3 - 5 - The First End-of-Discharge Voltage flag (EDV1), bit 1, is set when Voltage < EDV1 and SEDV = 0 and cleared when VQ = 1 and Voltage > EDV1. Bits 7 and 6 are reserved. 5 VQ 6 - Where SEDV is: FLAGS1 6 - Self-discharge is greater than 256mAh, EDV1 = 1 when T < 0°C or VQ = 1 The Stop EDV flag (SEDV), bit 2, is set when the discharge current > 6.15A and cleared when the discharge current falls below 6.15A. 0 OC Where OC is: 7 - 0 0 VQ = 1 and Voltage > EDVF 1 Voltage < EDVF and SEDV = 0 Error Codes and Status Bits 0 - Error codes and status bits are listed in Table 8 and Table 9, respectively. Where VDQ is: 19 bq2945 Control Pins 1 and 2 (CP1, CP2) Programming the bq2945 CP1 and CP2 are open drain outputs that are controlled by host command. Since they are under the control of the host, their use can be defined by the pack designer. Some uses for these pins are charger control, control of current path (charge FET, discharge FET, or fuse), or special LED function. CP1 and CP2 are controlled by the host writing a command to the battery’s ManufacturerAccess slave function. Table 7 describes the commands that are available to control CP1 and CP2. The bq2945 requires the proper programming of an external EEPROM for proper device operation. Each module can be calibrated for the greatest accuracy, or general “default” values can be used. An EV2200-45 programming kit (interface board, software, and cable) for an IBM-compatible PC is available from Unitrode. The bq2945 uses a 24LC01 or equivalent serial EEPROM (capable of read operation to 2.0V) for storing the various initial values, calibration data, and string information. Table 1 outlines the parameters and addresses for this information. Tables 10 and 11 detail the various register contents and show an example program value for an 2400mAh 4-series Li-Ion battery pack, using a 50mΩ sense resistor. The CP2 can also act as a digital input. The logical status can be monitored in bit 6 of the FLAGS2 register. Table 7. ManufactureAccess Commands CMD (0x00) = 0x0505 0x051b 0x0536 0x054e 0x0563 0x057d Action CP1 set to hi-Z CP1 set low CP2 set to hi-Z CP2 set low CP1 and CP2 set to hi-Z CP1 and CP2 set low SBD Seal The bq2945 address space can be “locked” to enforce the SBS specified access to each command code. To lock the address space, the bq2945 must be initialized with EE 0x3d set to 00h. Once this is done, only commands 0x00-0x04 may be written. Attempting to write to any other address will cause a “no acknowledge” of the data. Reading will only be permitted from the command codes listed in the SBD specification plus the five locations designated as optional manufacturing functions 1—5 (0x2f, 0x3c—0x3f). 20 bq2945 Table 8. Error Codes (BatteryStatus() (0x16)) Error Code Access Description OK 0x0000 read/write bq2945 processed the function code without detecting any errors. Busy 0x0001 read/write bq2945 is unable to process the function code at this time. ReservedCommand 0x0002 read/write UnsupportedCommand 0x0003 read/write bq2945 does not support the requested function code. AccessDenied 0x0004 Overflow/Underflow 0x0005 BadSize 0x0006 UnknownError 0x0007 Note: write bq2945 cannot read or write the data at this time—try again later. bq2945 detected an attempt to write to a read-only function code. read/write bq2945 detected a data overflow or underflow. write bq2945 detected an attempt to write to a function code with an incorrect size data block. read/write bq2945 detected an unidentifiable error. Reading the bq2945 after an error clears the error code. 21 bq2945 Table 9. BatteryStatus Bits Alarm Bits Bit Name Set When: Reset When: OVER_CHARGED_ALARM The bq2945 detects a ∆T/∆t or current taper termination. (Note: ∆T/∆t and current taper are valid charge terminations.) A discharge occurs or when the ∆T/∆t or current taper termination condition ceases during charge. TERMINATE_CHARGE_ALARM The bq2945 detects an over-current, over-voltage, over-temperature, ∆T/∆t, or current taper condition during charge. A discharge occurs or when all conditions causing the event cease. OVER_TEMP_ALARM The bq2945 detects that its internal temperature is greater than the programmed value. Internal temperature falls below 50°C. TERMINATE_DISCHARGE_ALARM The bq2945 determines that it has supplied all the charge that it can without being damaged (Voltage < EDVF). Voltage > EDVF signifies that the battery has reached a state of charge sufficient for it to once again safely supply power. REMAINING_CAPACITY_ALARM Either the value set by the RemainThe bq2945 detects that the RemainingCapacityAlarm function is lower ingCapacity is less than that set by than the Remaining Capacity or the the RemainingCapacityAlarm funcRemainingCapacity is increased by tion. charging. REMAINING_TIME_ALARM The bq2945 detects that the estimated remaining time at the present discharge rate is less than that set by the RemainingTimeAlarm function. Either the value set by the RemainingTimeAlarm function is lower than the AverageTimeToEmpty or a valid charge is detected. Status Bits Bit Name Set When: Reset When: INITIALIZED The bq2945 has completed a “learn” cycle. DISCHARGING The bq2945 determines that it is not Battery detects that it is being being charged. charged. FULLY_CHARGED The bq2945 determines a valid charge termination or a maximum overcharge state. RM discharges below 95% of the full charge percentage. FULLY_DISCHARGED bq2945 determines that it has supplied all the charge that it can without being damaged. RelativeStateOfCharge is greater than or equal to 20% 22 Battery detects that power-on or user-initiated reset has occurred. bq2945 Table 10. Example Register Contents EEPROM Address Description Low Byte High Byte EEPROM Hex Contents Low Byte High Byte Example Values Notes EEPROM length 0x00 64 100 Must be equal to 0x64. EEPROM check 1 0x01 5b 91 Must be equal to 0x5b. Remaining time alarm 0x02 0x03 0a 00 Remaining capacity alarm 0x04 0x05 f0 00 240mAh Sets the low capacity alarm level. Reserved 0x06 0x07 00 00 0 Not currently used by the bq2945. Initial charging current 0x08 0x09 60 09 2400mA Sets the initial charge request. Charging voltage 0x0a 0x0b d8 40 16600mV Used to set the fast-charge voltage for the Smart Charger. Battery status 0x0c 0x0d 80 00 128 Cycle count 0x0e 0x0f 00 00 0 Design capacity 0x10 0x11 60 09 2400mAh Nominal battery pack capacity. Design voltage 0x12 0x13 40 38 14400mV Nominal battery pack voltage. Specification information 0x14 0x15 10 00 1.0 Manufacturer date 0x16 0x17 a1 20 Serial number 0x18 0x19 12 27 10002 Fast-charging current 0x1a 0x1b 60 09 2400mA Maintenance charge current 0x1c 0x1d 00 00 0mA Reserved 0x1e 0x1f 00 00 0 Current integration gain1 Note: 0x2c 0x2d 40 00 10 minutes Sets the low time alarm level. Initializes BatteryStatus. Contains the charge cycle count and can be set to zero for a new battery. Default value for this register in a 1.0 part. May 1, 1996 Packed per the ManufactureDate description. = 8353 Contains the optional pack serial number. Used to set the fast-charge current for the Smart Charger. Contains the desired maintenance current after fastcharge termination by the bq2945. Must be programmed to 0x00. 3.2/0.05 1. Can be adjusted to calibrate the battery pack. 23 Represents the following: 3.2/sense resistor in ohms. It is used by the bq2945 to scale the measured voltage values on the SR pin in mA and mAh. This register also compensates for variations in the reported sense resistor value. bq2945 Table 10. Example Register Contents (Continued) EEPROM Address EEPROM Hex Contents Low Byte High Byte Reserved 0x2e 0x2f 00 00 0 Li-Ion taper current 0x38 0x39 10 ff 240mA Sets the upper taper limit for Li-Ion charge termination. Stored in 2’s complement. Maximum overcharge limit 0x3a 0x3b 9c ff 100mAh Sets the maximum amount of overcharge before a maximum overcharge charge suspend occurs. Stored in 2’s complement. Reserved 0x3c 00 Access protect 0x3d 00 FLAGS1 0x3e 00 FLAGS2 0x3f b0 Battery voltage 0x48 offset1 fe Description Temperature offset1 0x49 Maximum temperature and 0x4a ∆T step Charge efficiency 0x4b Full-charge percentage Note: 0x4c Low High Byte Byte 8a Example Values Notes Not currently used by the bq2945. 0 Should be programmed to 0. If the bq2945 is reset and this location is 0, the SBD access only bq2945 locks access to any command outside of the SBD data set. Program to 0x08 for full R/W access. 0 Initializes FLAGS1 Relative display Li-Ion chemistry Initializes FLAGS2. bq2945 charge control -2mV Used to adjust the battery voltage offset according to the following: Voltage = (VSB(mV) + VOFF) ∗ Voltage gain 13.8°C The default value (zero adjustment) for the offset is 12.8°C or 0x80. TOFFNEW = TOFFCURRENT + (TEMPACTUAL - TEMPREPORTED)∗ 10 8f Maximum Maximum charge temperature is 74 - (mt ∗ 1.6)°C (mt temperature = = upper nibble). The ∆T step is (dT ∗ 2 + 16)/10°C 61.2°C (dT = lower nibble) ∆T step = 4.6°C ff Maintenance compensation = 100% Fast compensation = 100% Sets the fast-charge (high) and maintenance charge (low) efficiencies. The upper nibbles sets the low efficiency and the lower nibble adjusts the high efficiency according to the equation: Nibble = (efficiency% ∗ 256 - 196)/4 100% This packed field is the two’s complement of the desired value in RM when the bq2945 determines a full-charge termination. If RM is below this value, RM is set to this value. If RM is above this value, then RM is not adjusted. 9c 1. Can be adjusted to calibrate the battery pack. 24 bq2945 Table 10. Example Register Contents (Continued) EEPROM Address Description EEPROM Hex Contents Low High Low High Byte Byte Byte Byte Example Values Notes Used to set the digital magnitude filter as described in Table 2. Digital filter 0x4d 96 0.30mV Reserved 0x4e 00 0 Self-discharge rate 0x4f 2d 0.25% This packed field is the two’s complement of (52.73/x) where x is the desired self-discharge rate per day (%) at room temperature. Voltage gain1 0x56 0x57 17 07 7.09 Voltage gain is packed as two units. For example, (R4 + R5)/R4 = 7.09 would be stored as: whole number stored in 0x57 as 7 and the decimal component stored in 0x56 as 256 x 0.09 = 23 (= 17h). Reserved 0x58 0x59 00 00 0 Not currently used by the bq2945. Should be programmed to 0. Current measure0x5a 0x5b ment gain1 ee 02 750 The current gain measurement and current integration gain are related and defined for the bq2945 current measurement. This word equals 37.5/sense resistor value in ohms. End of discharge voltage1 0x5c 0x5d 20 d1 12000mV The value programmed is the two’s complement of the threshold voltage in mV. End of discharge voltage final 0x5e 0x5f 40 d4 11200mV The value programmed is the two’s complement of the threshold voltage in mV. Full charge capacity 0x60 0x61 d0 07 2000mA This value sets the initial estimated pack capacity. ∆t step 0x62 ff 20s The ∆t step for ∆T/∆t termination equals 20s ∗ the two’s complement of the byte value. Hold-off time 0x63 f0 320s hold-off b5 181 Must be equal to 0xb5. NA Not currently used by the bq2945. EEPROM check 2 0x64 Reserved Note: 0x65 0x7f The hold-off time is 20s ∗ the two’s complement of the byte value. 1. Can be adjusted to calibrate the battery pack. 25 bq2945 Table 11. Example Register Contents (String Data) String Description Address 0x X0 0x X1 0x X2 0x X3 0x X4 0x X5 0x X6 0x X7 0x X8 0x X9-Xf 0x xa 0x xb 52 R 51 Q - - Manufacturer name 0x200x2b 09 42 B 45 E 4e N 43 C 48 H 4d M 41 A Device name 0x300x37 06 42 B 51 Q 32 2 39 9 34 4 35 5 - Device chemistry 0x400x47 04 6c L 69 I 4f O 4e N - Manufacturer data 0x500x55 05 42 B 51 Q 32 2 30 0 32 2 26 bq2945 Absolute Maximum Ratings Minimum Maximum Unit VCC Symbol Relative to VSS -0.3 +7.0 V All other pins Relative to VSS -0.3 +7.0 V REF Relative to VSS -0.3 +8.5 V Current limited by R1 (See Figure 1.) VSR Relative to VSS -0.3 +7.0 V Minimum 100Ω series resistor should be used to protect SR in case of a shorted battery. TOPR Operating temperature 0 +70 °C Commercial Note: Parameter Notes 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. Exposure to conditions beyond the operational limits for extended periods of time may affect device reliability. DC Voltage Thresholds (TA = TOPR; V = 3.0 to 5.5V) Symbol Parameter Minimum Typical Maximum Unit -50mV - 50mV V Notes EVSB Battery voltage error relative to SB Note: The accuracy of the voltage measurement may be improved by adjusting the battery voltage offset and gain, stored in external EEPROM. For best operation, VCC should be 1.5V greater than VSB. 27 See note bq2945 Recommended DC Operating Conditions (TA = TOPR) Symbol VCC VREF RREF ICC Parameter Minimum Typical Maximum Unit Notes Supply voltage 3.0 4.25 6.5 V VCC excursion from < 2.0V to ≥ 3.0V initializes the unit. Reference at 25°C 5.7 6.0 6.3 V IREF = 5µA Reference at -40°C to +85°C 4.5 - 7.5 V IREF = 5µA Reference input impedance 2.0 5.0 - MΩ VREF = 3V - 90 135 µA VCC = 3.0V - 120 180 µA VCC = 4.25V - 170 250 µA VCC = 5.5V Normal operation VSB Battery input 0 - VCC V RSBmax SB input impedance 10 - - MΩ 0 < VSB < VCC IDISP DISP input leakage - - 5 µA VDISP = VSS ILVOUT VOUT output leakage -0.2 - 0.2 µA EEPROM off VSR Sense resistor input -0.3 - 2.0 V VSR < VSS = discharge; VSR > VSS = charge RSR SR input impedance 10 - - MΩ -200mV < VSR < VCC VIH 0.5 ∗ VCC - VCC V ESCL, ESDA Logic input high 1.4 - 5.5 V SMBC, SMBD 0 - 0.3 ∗ VCC V ESCL, ESDA 0.6 V SMBC, SMBD IOL=350µA, SMBC, SMBD VIL Logic input low -0.5 VOL Data, clock output low - - 0.4 V IOL Sink current 100 - 350 µA VOL≤0.4V, SMBC, SMBD VOLSL LEDX , CP1, CP2 output low, low VCC - 0.1 - V VCC = 3V, IOLS ≤ 1.75mA LED1–LED5, CP1, CP2 VOLSH LEDX , CP1, CP2 output low, high VCC - 0.4 - V VCC = 6.5V, IOLS ≤ 11.0mA LED1–LED5, CP1, CP2 VOHVL VOUT output, low VCC VCC - 0.3 - - V VCC = 3V, IVOUT = -5.25mA VOHVH VOUT output, high VCC VCC - 0.6 - - V IVOUT VOUT source current -33 - - mA At VOHVH = VCC - 0.6V IOLS LEDX , CP1, CP2 sink current 11.0 - mA At VOLSH = 0.4V Note: All voltages relative to VSS. 28 VCC = 6.5V, IVOUT = -33.0mA bq2945 AC Specifications Min Max Units FSMB Symbol SMBus operating frequency Parameter 10 100 KHz TBUF Bus free time between stop and start condition 4.7 µs THD:STA Hold time after (repeated) start condition 4.0 µs TSU:STA Repeated start condition setup time 4.7 µs TSU:STO Stop condition setup time 4.0 µs THD:DAT Data hold time 300 ns TSU:DAT Data setup time 250 ns TLOW Clock low period 4.7 µs THIGH Clock high period 4.0 µs TF Clock/Data fall time 300 ns TR Clock/data rise time 1000 ns TLOW:SEXT Cumulative clock low extend time (slave) 25 ms 35 ms TTIMEOUT 25 Notes Bus Timing Data tR SMBC tHIGH tSU:STA tHD:STA tLOW tHD:DAT tSU:DAT tSU:STO SMBD tF tBUF TD294501.eps 29 bq2945 16-Pin SOIC Narrow (SN) 16-Pin SN (SOIC Narrow) D e Dimension Minimum A 0.060 A1 0.004 B 0.013 C 0.007 D 0.385 E 0.150 e 0.045 H 0.225 L 0.015 All dimensions are in inches. B E H A C A1 .004 L 30 Maximum 0.070 0.010 0.020 0.010 0.400 0.160 0.055 0.245 0.035 bq2945 Data Sheet Revision History ChangeNo. Page No. 1 All 2 6 Added VSB should not exceed 2.4V 2 11 Changed cycle count increase from 30 to 32 for condition request 2 14 Changed AtRateOK() indication from EDV1 to EDVF 2 25 Changed self discharge programming from 52.75/x to 52.73/x Notes: Description of Change “Final” changes from “Preliminary” version Change 1 = June 1998 B changes from Sept. 1997 “Preliminary.” Change 2 = June 1999 C changes from June 1998. Ordering Information bq2945 Temperature Range: blank = Commercial (0 to 70°C) Package Option: SN = 16-pin narrow SOIC Device: bq2945 Gas Gauge IC With SMBus Interface 31 IMPORTANT NOTICE Texas Instruments and its subsidiaries (TI) reserve the right to make changes to their products or to discontinue any product or service without notice, and advise customers to obtain the latest version of relevant information to verify, before placing orders, that information being relied on is current and complete. All products are sold subject to the terms and conditions of sale supplied at the time of order acknowledgement, including those pertaining to warranty, patent infringement, and limitation of liability. TI warrants performance of its semiconductor products to the specifications applicable at the time of sale in accordance with TI’s standard warranty. Testing and other quality control techniques are utilized to the extent TI deems necessary to support this warranty. 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