Not Recommended For New Designs bq2040 Gas Gauge IC With SMBus Interface Features General Description ➤ Provides accurate measurement of available charge in NiCd, NiMH, and Li-Ion batteries The bq2040 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 bq2040 directly supports capacity monitoring for NiCd, NiMH, and LiIon battery chemistries. ➤ Supports SBS v1.0 data set and two-wire interface ➤ Monitors charge FET in Li-Ion pack protection circuit ➤ 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 four-segment LED display for remaining capacity indication The bq2040 uses the System Management Bus v1.0 (SMBus) protocol and supports the Smart Battery Data (SBData) commands. The bq2040 also supports the SBData charge control functions. Battery state-of-charge, remaining capacity, remaining time, and chemistry are av ai l a b l e o v e r th e s e ri a l l i n k. Battery-charge state can be directly indicated using a four-segment LED display to graphically depict battery full-to-empty in 25% increments. The bq2040 estimates battery selfdischarge based on an internal timer and temperature sensor and user-programmable rate information stored in external EEPROM. The bq2040 also automatically recalibrates or “learns” battery capacity in the full course of a discharge cycle from full to empty. The bq2040 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 is used to program initial values into the bq2040 and is necessary for proper operation. ➤ 16-pin narrow SOIC Pin Connections Pin Names VCC 3.0–6.5V SB Battery sense input VCC 1 16 VOUT ESCL EEPROM clock PSTAT Protector status input ESCL 2 15 REF ESDA EEPROM data SMBD SMBus data input/output ESDA 3 14 SMBC LED1-4 LED segment 1-4 SMBC SMBus clock LED1 4 13 SMBD VSS System ground REF Voltage reference output LED2 5 12 PSTAT SR Sense resistor input VOUT EEPROM supply output LED3 6 11 SB DISP Display control input LED4 7 10 DISP VSS 8 9 SR 16-Pin Narrow SOIC PN204001.eps SLUS005–JUNE 1999 E 1 Not Recommended For New Designs bq2040 DISP Pin Descriptions VCC Supply voltage input ESCL Serial memory clock 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. Output used to clock the data transfer between the bq2040 and the external nonvolatile configuration memory. ESDA SB LED display segment outputs PSTAT Each output may drive an external LED. VSS Ground SR Sense resistor input 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. Serial memory data and address Bidirectional pin used to transfer address and data to and from the bq2040 and the external nonvolitile configuration memory. LED1– LED4 Display control input Protector status input Provides overvoltage status from the Li-Ion protector circuit and can initiate a charge suspend request. SMBD 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 bq2040 is VSR + VOS. (See Table 3.) SMBus data Open-drain bidirectional pin used to transfer address and data to and from the bq2040. SMBC SMBus clock Open-drain bidirectional pin used to clock the data transfer to and from the bq2040. REF Reference output for regulator REF provides a reference output for an optional FET-based micro-regulator. VOUT Supply output Supplies power to the external EEPROM configuration memory. 2 Not Recommended For New Designs bq2040 Figure 1 shows a typical battery pack application of the bq2040 using the LED capacity display, the serial port, and an external EEPROM for battery pack programming information. The bq2040 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 EEPROM. Functional Description General Operation The bq2040 determines battery capacity by monitoring the amount of charge put into or removed from a rechargeable battery. The bq2040 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. (Optional) VCC VOUT ESCL ESDA LED1 LED2 LED3 LED4 VSS REF SMBC SMBD PSTAT SB DISP SR bq2040 Chart 1 For bq2040 With No D8 NiMH Li-Ion No. of Cells R5 R11 R4 Q1 2 301K 604K 100K BSS138 3 4 499K 806K 100K BSS138 698K 604K 100K 2N7002 6 499K 499K 100K BSS138 8 698K 806K 100K BSS138 9 806K 499K 100K 2N7002 10 909K 604K 100K 2N7002 12 909K 909K 86.5K 2N7002 (Optional) 2040LED.eps Figure 1. Battery Pack Application Diagram—LED Display 3 Not Recommended For New Designs bq2040 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 Manufacture 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 overload 0x2c/0x2d Sets the overload current threshold 16 bits mA Battery low % 0x2e Sets the battery low amount 8 bits % Reserved 0x2f Reserved for future use 8 bits NA Device name 0x30-0x37 Programs DeviceName (0x21) 64 bits NA Li-Ion taper current Sets the upper limit of the taper current for charge 0x38/0x39 termination 16 bits mA Maximum overcharge limit 0x3a/0x3b Sets the maximum amount of overcharge 16 bits NA Reserved must = 0x00 8 bits NA 0x3d Locks commands outside of the SBS data set 8 bits NA 0x3e Initializes FLAGS1 8 bits NA 0x3f Initializes FLAGS2 8 bits NA Reserved 0x3c Access protect FLAGS1 FLAGS2 Device chemistry 0x40-0x45 Programs DeviceChemistry (0x22) 48 bits NA Current measurement gain 0x46/0x47 Sense resistor calibration value 16 bits NA Battery voltage offset 0x48 Voltage calibration value 8 bits NA Temperature offset 0x49 Temperature calibration value 8 bits NA Maximum temperature and ∆T step 0x4a Sets the maximum charge temperature and the ∆T step for ∆T/∆t termination 8 bits NA 4 Not Recommended For New Designs bq2040 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 Current integration gain 0x4e Programs the current integration gain to the sense resistor value 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 EDVF charging current Sets the charge current request when the battery 0x5a/0x5b voltage is less than EDVF 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 Sets the ∆t step for ∆T/∆t termination 8 bits NA ∆t step 0x62 Hold-off time 0x63 Sets ∆T/∆t hold-off timer 8 bits NA 0x64 EEPROM data integrity check byte must = 0xb5 8 bits NA EEPROM check 2 Reserved 0x65-0x7f Reserved for future use 5 NA Not Recommended For New Designs bq2040 Voltage Thresholds Layout Considerations In conjunction with monitoring VSR for charge/discharge currents, the bq2040 monitors the battery potential through the SB pin. The voltage potential is determined through a resistor-divider network per the following equation: The bq2040 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. 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 a programmable “empty” state. The bq2040 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 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 bq2040 should be in thermal contact with the cells for optimum temperature measurement. Gas Gauge Operation The operational overview diagram in Figure 2 illustrates the operation of the bq2040. The bq2040 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. 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. EDV monitoring may be disabled under certain conditions. If the discharge current is greater than the value stored in location 0x2c and 0x2d in the EEPROM (EE 0x2c/0x2d), EDV monitoring is disabled and resumes after the current falls below the programmed value. 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 bq2040 is reset when first connected to the battery pack. On power-up, the bq2040 initializes and reads the EEPROM configuration memory. The bq2040 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 bq2040 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 bq2040 adapts its capacity determination based on the actual conditions of discharge. 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. Temperature The battery’s empty state is also programmed in the EEPROM. The battery low percentage (EE 0x2e) stores the percentage of FCC that will be written to RM when the battery voltage drops below the EDV1 threshold. The bq2040 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 bq2040 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. Dur- 6 Not Recommended For New Designs bq2040 Inputs Charge Current 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 Outputs Chip-Controlled Two-Wire Available Charge Serial Interface LED Display FG294501.eps Figure 2. Operational Overview ing subsequent discharges, FCC is updated with the latest measured capacity in the Discharge Count Register plus the battery low amount, 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 bq2040 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. 3. 4. 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, both discharge and self-discharge increment the DCR. After RM = 0, only discharge increments the DCR. The DCR resets to 0 when RM = FCC and stops counting at EDV1 on discharge. The DCR does not roll over but stops counting when it reaches FFFFh. 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. FCC is updated on the first charge after a qualified discharge to EDV1. The updated FCC equals the battery low percentage times the current FCC plus the DCR value. A qualified discharge to EDV1 occurs if all of the following conditions exist: 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 the battery low amount after the EDV1 threshold has been reached. If RM is already equal to or less than the battery low amount, RM is not modified. If RM reaches the battery low amount before the battery voltage falls below EDV1 on discharge, RM stops counting down until the EDV1 threshold is reached. RM is set to 0 when the battery voltage reaches EDVF. To prevent overstatement of charge during periods of overcharge, RM stops incrementing when RM = FCC. RM may optionally be written to a user-defined value when fully charged if the battery pack is under bq2040 charge control. On initialization, RM is set to 0. n n 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 low temperature fault bit in FLAGS2 is not set when the EDV1 level is reached during discharge. Battery voltage is not more than 256mV below the EDV1 threshold when EDV1 is set. 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. 7 Not Recommended For New Designs bq2040 Charge Counting Current Taper Charge activity is detected based on a positive voltage on the SR input. If charge activity is detected, the bq2040 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. For Li-Ion charge control, the ChargingVoltage must be set to the desired pack voltage during the constant voltage charge phase. The bq2040 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 less than the programmed threshold in EE 0x38—0x39 and non-zero for at least 100s. The bq2040 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. ∆T/∆t The ∆T/∆t used by the bq2040 is programmable in both the temperature step (1.6°C–4.6°C) and time step (20 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. Discharge Counting ∆T ∆T is set by the formula: = ∆t ∆t 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. [(lower nibble of EE 0x4a)∗ 2 + 16 ] / 10 [320 − (EE 0x62) ∗ 20)] Self-Discharge Estimation 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. The bq2040 continuously decrements RM and increments DCR for self-discharge based on time and temperature provided that the discharge flag in BatteryStatus is set (charge not detected). The bq2040 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 approximately doubles for every 10°C increase until the temperature is ≥ 70°C or halves every 10°C decrease until the temperature is < 10°C. Charge Termination Charge Control Once the bq2040 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 te rmi n a ti n g co n d i ti o n s ce a s e, th e Te rm inate_Charge_Alarm and the Over_Charged_Alarm are cleared, and the requested charging current is set to the maintenance rate. The bq2040 requests the maintenance rate until RM falls below the amount determined by the programmable 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. The bq2040 supports SBS charge control by broadcasting the ChargingCurrent and the ChargingVoltage to the Smart Charger address. The bq2040 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 bq2040 updates the value used in the charging current broadcasts based on the battery’s state of charge, voltage, and temperature. The bq2040 internal charge control is compatible with nickel-based and Li-Ion chemistries. The bq2040 uses current taper detection for Li-Ion primary charge termination and ∆T/∆t for nickel based primary charge termination. The bq2040 also provides a number of safety terminations based on battery capacity, 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. 8 Not Recommended For New Designs bq2040 Charge Suspension Count Compensations The bq2040 may temporarily suspend charge if it detects a charging fault. The charging faults include the following conditions: 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. n Maximum Overcharge: If charging continues for more than the programmed maximum overcharge limit as defined in EE 0x3a—0x3b beyond RM=FCC, the Fully_Charged bit is set, and the requested charging current is set to the maintenance rate. Charge Compensation Charge efficiency is compensated for state-of-charge, temperature, and battery chemistry. The charge efficiency is adjusted using the following equations: n Overvoltage: An over-voltage fault exists when the bq2040 measures a voltage more than 5% above the ChargingVoltage. When the bq2040 detects an overvoltage condition, the requested charge current is set to 0 and the Terminate_Charge_Alarm bit is set in BatteryStatus. The alarm bit is cleared when the current drops below 256mA and the voltage is less than 105% of ChargingVoltage. 1.) RM = RM * (Q EFC − Q ET ) where RelativeStateOfCharge < FullChargePercentage, and Q EFC is the programmed fast-charge efficiency varying from 0.75 to 1.0. 2.) RM = RM * (Q ETC − Q ET ) where RelativeStateOfCharge ≥ FullChargePercentage and Q ETC is the programmed maintenance (trickle) charge efficiency varying from 0.75 to 1.0. n Overcurrent: An overcurrent fault exists when the bq2040 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 1mA above the lowest multiple of 256mA that exceeds the ChargingCurrent. When the bq2040 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 is used to adjust the charge efficiency as the battery temperature increases according to the following: Q ET = 0 if T < 30°C Q ET = 0.02 if 30 ° C ≤ T < 40 ° C Q ET = 0.05 if T ≥ 40 ° C QET is 0 over the entire temperature range for Li-Ion. n Maximum Temperature: When the battery temperature equals 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 Over_Temp_Alarm bit is cleared when the temperature drops to 43°C below the maximum temperature threshold minus 5°C. Digital Magnitude Filter The bq2040 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. n PSTAT: When the PSTAT input is ≥1.5V, the requested charge current is set to 0 and the Terminate_Charge_Alarm bit is set in BatteryStatus if the Discharging flag is not set. The alarm bit is cleared when the PSTAT input is <1.0V or the Discharging flag is set. DMF = 45 VSRD Table 2. Typical Digital Filter Settings n Low Temperature: When the battery temperature is less than 12°C (LTF bit in FLAGS2 set), the requested charge current is set to the maintenance rate. Once the temperature is above 15°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 EDVF rate stored in EE0x5a/0x5b. Once the voltage is above EDVF, the requested charge current is set to the fast or maintenance rate depending on the state of the LTF bit. 9 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 Not Recommended For New Designs bq2040 Table 3. bq2040 Current-Sensing Errors Symbol Parameter VOS Offset referred to VSR INL Integrated non-linearity error INR Integrated nonrepeatability error Typical Maximum Units ± 75 ± 150 µV Notes DISP = VCC. ±1 ±4 % Add 0.1% per °C above or below 25°C and 1% per volt above or below 4.25V. ± 0.5 ±1 % Measurement repeatability given similar operating conditions. and Remaining_Capacity_Alarm is set. VSB below EDVF (EDVF = 1) disables the display output. Error Summary Capacity Inaccurate Microregulator 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. The bq2040 can operate directly from three nickel chemistry cells. To facilitate the power supply requirements of the bq2040, an REF output is provided to regulate an external low-threshold n-FET. A micropower source for the bq2040 can be built inexpensively 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. Current-Sensing Error Communicating With the bq2040 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. The bq2040 includes a simple two-pin (SMBC and SMBD) bi-directional serial data interface. A host processor uses the interface to access various bq2040 registers; see Table 4. This method allows battery characteristics to be monitored easily. The open-drain SMBD and SMBC pins on the bq2040 are pulled up by the host system, or may be connected to VSS, if the serial interface is not used. Display The bq2040 can directly display capacity information using low-power LEDs. The bq2040 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 25% of the FCC. The interface uses a command-based protocol, where the host processor sends the battery address and an eightbit command byte to the bq2040. The command directs the bq2040 to either store the next data received to a register specified by the command byte or output the data specified by the command byte. In absolute mode, each segment represents a fixed amount of charge, 25% 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. bq2040 Data Protocols 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 bq2040. (See Figure 3). When DISP is tied to VCC, the LED1-4 outputs are inactive. When DISP is left floating, the display becomes active whenever the bq2040 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. Host-to-bq2040 Message Protocol The Bus Host communicates with the bq2040 using one of three protocols: LED1 blinks at a 4Hz rate indicating a low battery condition whenever the display is active, EDVF is not set, 10 n Read word n Write word Not Recommended For New Designs bq2040 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 bq2040 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 FG204001.eps Figure 3. Host Communication Protocols n Input/Output: unsigned integer. This sets/returns the value where the Remaining_Time_Alarm bit is set in Battery Status. Read block The particular protocol used is a function of the command. The protocols used are shown in Figure 3. Units: minutes Host-to-bq2040 Messages (see Table 4) Range: 0 to 65,535 minutes ManufacturerAccess() (0x00) BatteryMode() (0x03) This read/write word is an open location. This read/write word selects the various battery operational modes. The bq2040 supports the battery capacity information specified in mAh. This function also determines whether the bq2040 charging values are broadcasted to the Smart Battery Charger address. Input/Output: word. RemainingCapacityAlarm() (0x01) 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. 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). 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. Input/Output: unsigned integer. This sets/returns the value where the Remaining_Capacity_Alarm bit is set in Battery Status. Units: mAh Bit 7 is the condition request flag. It is set when the bq2040 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. Range: 0 to 65,535mAh RemainingTimeAlarm() (0x02) AtRate() (0x04) 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. 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. 11 Not Recommended For New Designs bq2040 Table 4. bq2040 Register Functions Function Code Access Units Defaults1 ManufacturerAccess 0x00 read/write - - RemaningCapacityAlarm 0x01 read/write mAh E2 RemainingTimeAlarm 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 SpecificationInfo 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 Not Recommended For New Designs bq2040 Table 4. bq2040 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 Not Recommended For New Designs bq2040 n n When the AtRate value is positive, the AtRateTimeToFull function returns the predicted time to full-charge at the AtRate value of charge. Temperature() (0x08) This read-only word returns the cell-pack's internal temperature. 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. Output: unsigned integer. Returns the predicted time to full charge. Units: mV 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 Output: unsigned integer. Returns the predicted time to empty. Range: 0 to 32,767mA for charge or 0 to –32,768mA for discharge Units: minutes Granularity: 0.2% of the DesignCapacity or better Range: 0 to 65,534min Accuracy: ± 1% of the DesignCapacity after calibration Granularity: 2min or better AverageCurrent() (0x0b) Invalid Data Indication: 65,535 indicates that the AtRate value is not negative. 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. AtRateOK() (0x07) This read-only word returns a Boolean value that indicates whether or not the EDVF flag has been set. Output: signed integer. Returns the charge/discharge rate in mA, where positive is for charge and negative is for discharge 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 14 Not Recommended For New Designs bq2040 Accuracy: ± 1% of the DesignCapacity after calibration RemainingCapacity() (0x0f) This read-only word returns the predicted remaining battery capacity. The RemainingCapacity value is expressed in mAh. MaxError() (0x0c) Returns the expected margin of error (%) in the state of charge calculation. Output: unsigned integer. Returns the estimated remaining capacity in mAh. Output: unsigned integer. Returns the percent uncertainty for selected information. Units: mAh Units: % Range: 0 to 65,535mAh Range: 0 to 100% Granularity: 0.2% of DesignCapacity or better Accuracy: ±MaxError ∗ FCC after circuit and capacity calibration 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. 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. Output: unsigned integer. Returns the percent of remaining capacity. Units: % Range: 0 to 100% Output: unsigned integer. Returns the estimated full charge capacity in mAh. Granularity: 1% Units: mAh Accuracy: ±MaxError after circuit and capacity calibration Range: 0 to 65,535mAh Granularity: 0.2% of DesignCapacity or better AbsoluteStateOfCharge() (0x0e) Accuracy: ±MaxError ∗ FCC after circuit and capacity calibration 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. RunTimeToEmpty() (0x11) 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. Output: unsigned integer. Returns the percent of remaining capacity. Units: % Output: unsigned integer. Returns the minutes of operation left. Range: 0 to 65,535% Units: minutes Granularity: 1% Range: 0 to 65,534min Accuracy: ±MaxError after circuit and capacity calibration Granularity: 2min or better Invalid data indication: 65,535 indicates battery is not being discharged. AverageTimeToEmpty() (0x12) This read-only word returns the predicted remaining battery life at the present average discharge rate (minutes). The AverageTimeToEmpty is calculated based on AverageCurrent. 15 Not Recommended For New Designs bq2040 Output: unsigned integer. Returns the minutes of operation left. BatteryStatus() (0x16) This read-only word returns the battery status word. Units: minutes Output: unsigned integer. Returns the status register with alarm conditions bitmapped as shown in Table 5. Range: 0 to 65,534min Granularity: 2min 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. Invalid data indication: 65,535 indicates battery is not being discharged. AverageTimeToFull() (0x13) Table 5. Status Register This read-only word returns the predicted time until the Smart Battery reaches full charge at the present average charge rate (minutes). Alarm Bits Output: unsigned integer. Returns the remaining time in minutes to full. 0x8000 Over_Charged_Alarm 0x4000 Terminate_Charge_Alarm Units: minutes 0x2000 Reserved Range: 0 to 65,534min 0x1000 Over_Temp_Alarm Granularity: 2min or better 0x0800 Terminate_Discharge_Alarm 0x0400 Reserved 0x0200 Remaining_Capacity_Alarm 0x0100 Remaining_Time_Alarm If enabled, the bq2040 sends the desired charging rate in mA to the Smart Battery Charger. 0x0080 Initialized 0x0040 Discharging Output: unsigned integer. Transmits/returns the maximum charger output current in mA. 0x0020 Fully_Charged 0x0010 Fully_Discharged Invalid data indication: 65,535 indicates battery is not being charged. ChargingCurrent() (0x14) Status Bits Units: mA Error Code Range: 0 to 65,534mA 0x00000x000f Granularity: 0.2% of the design capacity or better Invalid data indication: 65,535 indicates that the Smart Charger should operate as a voltage source outside its maximum regulated current range. Reserved for error codes 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 bq2040 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. ChargingVoltage() (0x15) If enabled, the bq2040 sends the desired voltage in mV to the Smart Battery Charger. Output: unsigned integer. Transmits/returns the charger voltage output in mV. Units: mV Range: 0 to 65,534mV Output: unsigned integer. Returns the count of charge/discharge cycles the battery has experienced. 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. Units: cycles 16 Not Recommended For New Designs bq2040 Table 6. Bit Descriptions for FLAGS1 and FLAGS2 (MSB) 7 FLAGS2 DMODE FLAGS1 Note: 6 5 4 3 2 1 0 (LSB) PSTAT CHM CC - OV LTF OC IMIN VQ - VDQ OVLD EDV1 EDVF ∆T/∆t - = Reserved Range: 0 to 65,535 cycles; 65,535 indicates battery has experienced 65,535 or more cycles. 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. Granularity: 1 cycle DesignCapacity() (0x18) This read-only word returns the theoretical capacity of a new pack. The DesignCapacity value is expressed in mAh at the nominal discharge rate. Output: unsigned integer ManufacturerName() (0x20) Output: unsigned integer. Returns the battery capacity in mAh. 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, “Benchmarq” identifies the battery pack manufacturer as Benchmarq. Units: mAh Range: 0 to 65,535mAh DesignVoltage() (0x19) Output: string or ASCII character string This read-only word returns the theoretical voltage of a new pack in mV. DeviceName() (0x21) 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 “bq2040” indicates that the battery is a model bq2040. Output: unsigned integer. Returns the battery's normal terminal voltage in mV. Units: mV Range: 0 to 65,535mV Output: string or ASCII character string SpecificationInfo() (0x1a) DeviceChemistry() (0x22) This read-only word returns the specification revision the bq2040 supports. 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. ManufactureDate() (0x1b) 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. Output: string or ASCII character string Field Bits Used Format ManufacturerData() (0x23) Allowable Value Day 0–4 5-bit binary 1–31 (corresponds to value date) Month 5–8 4-bit binary 1–12 (corresponds to value month number) Year 9–15 7-bit binary 0–127 (corresponds to value year biased by 1980) 17 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. Not Recommended For New Designs bq2040 The CHM value is: End of Discharge Voltage1 (0x3e) This read-only word returns the first end-of-discharge voltage programmed for the pack. 7 - Output: two’s complemented unsigned integer. Returns battery end-of-discharge voltage programmed in EEPROM in mV. 6 - 5 CHM FLAGS2 Bits 4 3 - 2 - 1 - Where CHM is: End of Discharge VoltageF (0x3f) This read-only word returns the final end-of-discharge voltage programmed for the pack. 0 Selects Nickel 1 Selects Li-Ion Bit 4, the Charge Control flag (CC), determines whether a bq2040-based charge termination will set RM to a user-defined programmable full charge capacity. Output: two’s complemented unsigned integer. Returns battery final end-of-discharge voltage programmed in EEPROM in mV. The CC value is: FLAGS1&2() (0x2f) This read-only register returns an unsigned integer representing the internal status registers of the bq2040. The MSB represents FLAGS2, and the LSB represents FLAGS1. See Table 6 for the bit description for FLAGS1 and FLAGS2. 7 - 6 - 5 - FLAGS2 Bits 4 3 CC - 2 - 1 - 0 The Display Mode flag (DMODE), bit 7 determines whether the bq2040 displays Relative or Absolute capacity. RM is not modified on valid bq2040 charge termination 1 RM is set to a programmable percentage of the FCC when a valid bq2040 charge termination occurs The DMODE value is: 7 DMODE 6 - Bit 3 is reserved. 2 - 1 - Bit 2, the Overvoltage flag (OV), is set when the bq2040 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. 0 - Where DMODE is: The OV value is: 0 Selects Absolute display 1 Selects Relative display 7 - Bit 6 reflects the high/low state of PSTAT. PSTAT ≥1.5V generates a charge suspend condition. The PSTAT value is: 7 - 6 PSTAT 0 - Where CC is: FLAGS2 FLAGS2 Bits 5 4 3 - 0 - FLAGS2 Bits 5 4 3 - PSTAT input < 1.0V 1 PSTAT input ≥ 1.5V 5 - FLAGS2 Bits 4 3 - 2 OV 1 - 0 - Where OV is: 2 - 1 - 0 - 0 Voltage < 1.05 ∗ ChargingVoltage 1 Voltage ≥ 1.05 ∗ ChargingVoltage Bit 1, the Low Temperature Fault flag (LTF), is set when Temperature is < 12°C and cleared when Temperature is ≥ 15°C. Where PSTAT is: 0 6 - The LTF value is: The Chemistry flag (CHM), bit 5, selects Li-Ion or nickel compensation factors. 7 - 18 6 - 5 - FLAGS2 Bits 4 3 - 2 - 1 LTF 0 - Not Recommended For New Designs bq2040 The IMIN value is: Where LTF is: 0 Temperature > 15°C 1 Temperature < 12°C Where IMIN is: Bit 0, the Overcurrent flag (OC), is set when Current is 25% greater than the programmed charging current. If the charging current is programmed less than 1024mA, overcurrent is set if Current is 256mA greater than the programmed charging current. This flag is cleared when Current falls below 256mA. 0 A valid current taper termination condition is not present. 1 Valid current taper termination condition detected. 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|. The OC value is: 7 - 6 - FLAGS2 Bits 4 3 2 - 5 - 1 - 7 - 0 OC 1 Current is less than 1.25 ∗ ChargingCurrent or less than 256mA if charging current is programmed less than 1024mA Current exceeds 1.25 ∗ ChargingCurrent or 256mA if the charging current is programmed less than 1024mA. This bit is cleared if Current < 256mA. 1 - 0 - FLAGS1 Bits 5 4 3 - 2 - 1 - 0 V SRO ≤ |V SRD | 1 V SRO ≥ |V SRD | and 10mAh of charge has accumulated 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. The ∆T/∆t value is: ∆T/∆t 2 - Bit 4 is reserved. Bits 7 indicates that a ∆T/∆t termination condition exists. 6 - FLAGS1 Bits 4 3 - Where VQ is: FLAGS1 7 5 VQ The VQ value is: Where OC is: 0 6 - 7 - 0 - 6 - 5 - FLAGS1 Bits 4 3 VDQ 2 - 1 - 0 - The VDQ value is: Where ∆T/∆t is: Where VDQ is: 0 The ∆T/∆t rate drops below the programmed rate. 1 The ∆T/∆t rate exceeds the programmed rate. 6 IMIN 5 - FLAGS1 Bits 4 3 - 2 - 1 - Self-discharge is greater than 256mAh, EDV1 = 1 when T < 0°C or VQ = 1 1 On first discharge after RM=FCC The Overload flag (OVLD), bit 2, is set when the discharge current is greater than the programmed rate and cleared when the discharge current falls below the programmed rate. Bit 6 indicates that a current taper termination condition exists. 7 - 0 0 - 7 - 19 6 - 5 - FLAGS1 Bits 4 3 2 OVLD 1 - 0 - Not Recommended For New Designs bq2040 The OVLD value is: SBD Seal Where OVLD is: 0 Current < programmed rate 1 Current > programmed rate The bq2040 address space can be “locked” to enforce the SBS specified access to each command code. To lock the address space, the bq2040 must be initialized with EE 0x3d set to b0h. 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). The First End-of-Discharge Voltage flag (EDV1), bit 1, is set when Voltage < EDV1 and OVLD = 0 and cleared when VQ = 1 and Voltage > EDV1. 7 - 6 - 5 - FLAGS1 Bits 4 3 2 - 1 EDV1 0 - Programming the bq2040 The EDV1 value is: The bq2040 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 EV2200-40 programming kit (interface board, software, and cable) for an IBM-compatible PC is available from Benchmarq. Where EDV1 is: 0 VQ = 1 and Voltage > EDV1 1 Voltage < EDV1 and OVLD = 0 The Final End-of-Discharge Voltage flag (EDVF), bit 0, is set when Voltage < EDVF and OVLD = 0 and cleared when VQ = 1 and Voltage > EDVF. 7 - 6 - 5 - FLAGS1 Bits 4 3 2 - 1 - The bq2040 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. 0 EDVF The EDVF value is: Where EDVF is: 0 VQ = 1 and Voltage > EDVF 1 Voltage < EDVF and OVLD = 0 Error Codes and Status Bits Error codes and status bits are listed in Table 8 and Table 9, respectively. 20 Not Recommended For New Designs bq2040 Table 8. Error Codes (BatteryStatus() (0x16)) Error Code Access Description OK 0x0000 read/write bq2040 processed the function code without detecting any errors. Busy 0x0001 read/write bq2040 is unable to process the function code at this time. ReservedCommand 0x0002 read/write UnsupportedCommand 0x0003 read/write bq2040 does not support the requested function code. AccessDenied 0x0004 Overflow/Underflow 0x0005 BadSize 0x0006 UnknownError 0x0007 Note: write bq2040 cannot read or write the data at this time—try again later. bq2040 detected an attempt to write to a read-only function code. read/write bq2040 detected a data overflow or underflow. write bq2040 detected an attempt to write to a function code with an incorrect size data block. read/write bq2040 detected an unidentifiable error. Reading the bq2040 after an error clears the error code. 21 Not Recommended For New Designs bq2040 Table 9. BatteryStatus Bits Alarm Bits Bit Name Set When: Reset When: OVER_CHARGED_ALARM The bq2040 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 bq2040 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 bq2040 detects that its internal temperature is greater than the programmed value. Internal temperature falls to 43°C or the maximum temperature threshold minus 5°C. TERMINATE_DISCHARGE_ALARM The bq2040 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 bq2040 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 bq2040 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 bq2040 loads from the EEPROM A bad EEPROM load is detected. (bit 7 set in EE0x0c). DISCHARGING The bq2040 determines that it is not Battery detects that it is being being charged. charged. FULLY_CHARGED The bq2040 determines a valid charge termination or a maximum overcharge state. RM discharges below the full charge percentage. FULLY_DISCHARGED bq2040 determines that it has supplied all the charge that it can without being damaged. RelativeStateOfCharge is greater than or equal to 20% 22 Not Recommended For New Designs bq2040 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 bq2040. 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 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. Design capacity 0x10 0x11 60 09 2400mAh Normal battery pack capacity. Design voltage 0x12 0x13 40 38 14400mV Nominal battery pack voltage. Specification information 0x14 0x15 10 00 1.0 Manufacture date 0x16 0x17 a1 20 Serial number 0x18 0x19 12 27 Default value for this register in a 1.0 part. May 1, 1996 Packed per the ManufactureDate description. = 8353 10002 Fast-charging current 0x1a 0x1b 60 09 2400mA Maintenance charge current 0x1c 0x1d 00 00 0mA Reserved 0x1e 0x1f 00 00 0 Current overload 0x2c Battery low % 0x2e 0x2d 70 08 17 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 bq2040. Must be programmed to 0x00. 6000mA Sets the discharge current at which EDV threshold monitoring is disabled. Sets the battery capacity that RemainingCapacity is reduced to at EDV1. The value equals 2.56 ∗ (%RM at EDV1) 3% 23 Not Recommended For New Designs bq2040 Table 10. Example Register Contents (Continued) EEPROM Address Description Low Byte High Byte EEPROM Hex Contents Low High Byte Byte 00 Example Values Reserved 0x2f Li-Ion taper current 0x38 0x39 10 ff 240mA Sets the upper taper limit for Li-Ion charge termination. Stored in 2’s complement. Maxi m um overcha r g e lim it 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 b0 FLAGS1 0x3e 00 FLAGS2 0x3f Current measurement gain1 0x46 Battery voltage 0x48 offset1 0 Notes 0 00 fe Must be programmed to 0. If the bq2040 is reset and bit 3 of this location is 0, the bq2040 locks access to any command outside of the SBS SBD access only data set. Program to 0xb8 for full R/W access, 0xb0 for SBD access only. 0 Initializes FLAGS1 Relative display Li-Ion chemistry Initializes FLAGS2. bq2040 charge control b0 0x47 Not currently used by the bq2040. 0f 3840 The current gain measurement and current integration gain are related and defined for the bq2040 current measurement. This word equals 192/sense resistor value in ohms. -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 Temperature offset1 0x49 8a Maximum temperature and ∆T step 0x4a 5f Maximum Maximum charge temperature is 69- (mt ∗ 1.6)°C (mt temperature = = upper nibble). The ∆T step is (dT ∗ 2 + 16)/10°C 61.0°C (dT = lower nibble). ∆T step = 4.6°C ff Maintenance compensation = 100% Fast compensation = 100% Charge efficiency 0x4b Full-charge percentage Note: 0x4c 9c 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 This packed field is the two’s complement of the desired value in RM when the bq2040 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. 100% 1. Can be adjusted to calibrate the battery pack. 24 Not Recommended For New Designs bq2040 Table 10. Example Register Contents (Continued) EEPROM Address Description Digital filter EEPROM Hex Contents Low High Low High Byte Byte Byte Byte 0x4d 96 Example Values Notes 0.30mV Used to set the digital magnitude filter as described in Table 2. 3.2/0.05 Represents the following: 3.2/sense resistor in ohms. It is used by the bq2040 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. 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 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). Current integration gain1 0x4e 40 Self-discharge rate 0x4f 2d Voltage gain1 0x56 0x57 17 07 7.09 Reserved 0x58 0x59 00 00 0 EDVF charging current 0x5a 0x5b 64 00 100mA End of discharge voltage 1 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 0f Hold-off time 0x63 00 EEPROM check 2 0x64 b5 Reserved Note: 0x65 0x7f 0 Should be programmed to 0. Contains the desired charge current below EDVF. The ∆t step for ∆T/∆t termination equals 320 - (byte value ∗ 20). 20s 320s hold-off The hold-off time is 320 - (byte value ∗ 20). 181 Must be equal to 0xb5. NA Not currently used by the bq2040. 1. Can be adjusted to calibrate the battery pack. 25 Not Recommended For New Designs bq2040 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 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 30 0 34 4 30 0 - Device chemistry 0x400x45 04 6c L 69 I 4f O 4e N - Manufacturer data 0x500x55 05 42 B 51 Q 32 2 30 0 32 2 26 Not Recommended For New Designs bq2040 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 R11 (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 Not Recommended For New Designs bq2040 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 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 IOL Sink current VOLSL 0 < VSB < VCC - - 0.4 V 100 - 350 µA VOL≤0.4V, SMBC, SMBD LEDX output low, low VCC - 0.1 - V VCC = 3V, IOLS ≤ 1.75mA LED1–LED4 VOLSH LEDX output low, high VCC - 0.4 - V VCC = 6.5V, IOLS ≤ 11.0mA LED1–LED4 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 sink current 11.0 - mA At VOLSH = 0.4V Note: All voltages relative to VSS. 28 VCC = 6.5V, IVOUT = -33.0mA Not Recommended For New Designs bq2040 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 25 TTIMEOUT Notes Bus Timing Data tR SMBC tHIGH tSU:STA tHD:STA tLOW tHD:DAT tSU:DAT tSU:STO SMBD tF tBUF TD294501.eps 29 Not Recommended For New Designs bq2040 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 Not Recommended For New Designs bq2040 Data Sheet Revision History ChangeNo. Page No. 3 3 Updated recommended application schematic. 3 9 Changed overcurrent fault conditon for ChargingCurrent < 1024mA. 3 10 4Hz operation of LED clarification. 3 11 Added descriptions for bits 7 and 13 of BatteryMode. 3 14 AtRateTimeToEmpty and AtRateTimeToFull invalid data indication correction. 3 15, 16 RunTimeToEmpty, AverageTimeToEmpty and AverageTimeToFull invalid data indication corrections. 3 23 Notes: Description of Change Changed typical Battery low % value for Li-Ion with EDV1 = 3.0V/cell. 3 24 Li-Ion taper current is stored in 2’s complement. 3 24 Changed typical ∆T step and Full-charge percentage for Li-Ion. 3 25 Voltage gain is (R4 + R5)/R4. 3 25 Changed typical EDV1 and EDVF values for Li-Ion. 4 6 Added VSB should not exceed 2.4V 4 8 The self discharge rate approx imately doubles or halves 4 11 Changed cycle count increase from 30 to 32 for condition request. 4 14 Changed AtRateOK() indication from EDV1 to EDVF 4 25 Changed self-discharge programming from 52.75/x to 52.73/x. 4 25 Changed recommended EDVF charging current from 0mA to 100mA Changes 1 and 2 refer to the 1998 Data Book Change 3 = June1998 D changes from Jan. 1998 C. Change 4 = June 1999 E changes from June 1998 D. Ordering Information bq2040 Temperature Range: blank = Commercial (0 to 70°C) Package Option: SN = 16-pin narrow SOIC Device: bq2040 Gas Gauge IC With SMBus Interface 31 PACKAGE OPTION ADDENDUM www.ti.com 2-Oct-2015 PACKAGING INFORMATION Orderable Device Status (1) Package Type Package Pins Package Drawing Qty Eco Plan Lead/Ball Finish MSL Peak Temp (2) (6) (3) Op Temp (°C) Device Marking (4/5) BQ2040SN-C408 NRND SOIC D 16 40 Green (RoHS & no Sb/Br) CU NIPDAU Level-2-260C-1 YEAR 0 to 70 2040 C408 BQ2040SN-C408G4 NRND SOIC D 16 40 Green (RoHS & no Sb/Br) CU NIPDAU Level-2-260C-1 YEAR 0 to 70 2040 C408 BQ2040SN-C408TR NRND SOIC D 16 2500 Green (RoHS & no Sb/Br) CU NIPDAU Level-2-260C-1 YEAR 0 to 70 2040 C408 BQ2040SN-D111 NRND SOIC D 16 40 Green (RoHS & no Sb/Br) CU NIPDAU Level-2-260C-1 YEAR 0 to 70 2040 D111 BQ2040SN-D111G4 NRND SOIC D 16 40 Green (RoHS & no Sb/Br) CU NIPDAU Level-2-260C-1 YEAR 0 to 70 2040 D111 BQ2040SN-D111TR NRND SOIC D 16 2500 Green (RoHS & no Sb/Br) CU NIPDAU Level-2-260C-1 YEAR 0 to 70 2040 D111 BQ2040SN-D111TRG4 NRND SOIC D 16 2500 Green (RoHS & no Sb/Br) CU NIPDAU Level-2-260C-1 YEAR 0 to 70 2040 D111 (1) The marketing status values are defined as follows: ACTIVE: Product device recommended for new designs. LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect. NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design. PREVIEW: Device has been announced but is not in production. Samples may or may not be available. OBSOLETE: TI has discontinued the production of the device. (2) Eco Plan - The planned eco-friendly classification: Pb-Free (RoHS), Pb-Free (RoHS Exempt), or Green (RoHS & no Sb/Br) - please check http://www.ti.com/productcontent for the latest availability information and additional product content details. TBD: The Pb-Free/Green conversion plan has not been defined. Pb-Free (RoHS): TI's terms "Lead-Free" or "Pb-Free" mean semiconductor products that are compatible with the current RoHS requirements for all 6 substances, including the requirement that lead not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, TI Pb-Free products are suitable for use in specified lead-free processes. Pb-Free (RoHS Exempt): This component has a RoHS exemption for either 1) lead-based flip-chip solder bumps used between the die and package, or 2) lead-based die adhesive used between the die and leadframe. The component is otherwise considered Pb-Free (RoHS compatible) as defined above. Green (RoHS & no Sb/Br): TI defines "Green" to mean Pb-Free (RoHS compatible), and free of Bromine (Br) and Antimony (Sb) based flame retardants (Br or Sb do not exceed 0.1% by weight in homogeneous material) (3) MSL, Peak Temp. - The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature. (4) There may be additional marking, which relates to the logo, the lot trace code information, or the environmental category on the device. Addendum-Page 1 Samples PACKAGE OPTION ADDENDUM www.ti.com 2-Oct-2015 (5) Multiple Device Markings will be inside parentheses. Only one Device Marking contained in parentheses and separated by a "~" will appear on a device. If a line is indented then it is a continuation of the previous line and the two combined represent the entire Device Marking for that device. (6) Lead/Ball Finish - Orderable Devices may have multiple material finish options. Finish options are separated by a vertical ruled line. Lead/Ball Finish values may wrap to two lines if the finish value exceeds the maximum column width. Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is provided. TI bases its knowledge and belief on information provided by third parties, and makes no representation or warranty as to the accuracy of such information. Efforts are underway to better integrate information from third parties. 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Addendum-Page 2 PACKAGE MATERIALS INFORMATION www.ti.com 14-Jul-2012 TAPE AND REEL INFORMATION *All dimensions are nominal Device Package Package Pins Type Drawing SPQ Reel Reel A0 Diameter Width (mm) (mm) W1 (mm) B0 (mm) K0 (mm) P1 (mm) W Pin1 (mm) Quadrant BQ2040SN-C408TR SOIC D 16 2500 330.0 16.4 6.5 10.3 2.1 8.0 16.0 Q1 BQ2040SN-D111TR SOIC D 16 2500 330.0 16.4 6.5 10.3 2.1 8.0 16.0 Q1 Pack Materials-Page 1 PACKAGE MATERIALS INFORMATION www.ti.com 14-Jul-2012 *All dimensions are nominal Device Package Type Package Drawing Pins SPQ Length (mm) Width (mm) Height (mm) BQ2040SN-C408TR SOIC D 16 2500 367.0 367.0 38.0 BQ2040SN-D111TR SOIC D 16 2500 367.0 367.0 38.0 Pack Materials-Page 2 IMPORTANT NOTICE Texas Instruments Incorporated and its subsidiaries (TI) reserve the right to make corrections, enhancements, improvements and other changes to its semiconductor products and services per JESD46, latest issue, and to discontinue any product or service per JESD48, latest issue. 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