8.3.2.1 SOC Smoothing Feature

Rapid changes in operating conditions, such as temperature or discharge current, can lead to sudden changes in the algorithm's immediate calculation of RemainingCapacity( ), FullChargeCapacity( ), and StateOfCharge( ). SOC Smoothing provides filtered data to the host resulting in more gradual changes to SOC-related data when conditions vary and can provide a better end-user experience. The feature is enabled through Op Config [SMOOTHEN].

Table 1. SOC_INT Function Definition

Table 2. Battery Detection

8.4.1.1 POR and INITIALIZATION Modes

Upon Power On Reset (POR), the fuel gauge copies ROM-based configuration defaults to RAM and begins INITIALIZATION mode where essential data is initialized and will remain in INITIALIZATION mode as halted-CPU state when an adapter, or other power source is present to power the bq27425 (and system), yet no battery has been detected. The occurrence of POR or a Control( ) RESET subcommand will set the Flags( ) [ITPOR] status bit to indicate that RAM has returned to ROM default data. When battery insertion is detected, a series of initialization activities begin including an OCV measurement. In addition CONTROL_STATUS [QMAX_UP] and [RES_UP] bits are cleared to allow fast learning of Qmax and impedance.

Some commands, issued by a system processor, can be processed while the bq27425 is halted in this mode. The gauge will wake up to process the command, and then return to the halted state awaiting battery insertion. The current consumption of INITIALIZATION mode is similar to NORMAL mode.

8.4.1.2 CONFIG UPDATE Mode

If the application requires different configuration data for the bq27425. The host can update both NVM and RAM based parameters using the Control( ) SET_CFGUPDATE subcommand to enter CONFIG UPDATE mode as indicated by the Flags( ) [CFGUPMODE] status bit. In this mode, fuel gauging is suspended while the host uses the Extended Data Commands to modify the configuration data blocks. To resume fuel gauging, the host sends a Control( ) SOFT_RESETsubcommand to exit CONFIG UPDATE mode and clear both Flags( ) [ITPOR] and [CFGUPMODE] bits. After a time-out of approximately 240 seconds (4 minutes), the gauge will automatically exit CONFIG UPDATE mode if it has not received a SOFT_RESET subcommand from the host.

8.4.1.3 NORMAL Mode

The fuel gauge is in NORMAL mode when not in any other power mode. During this mode, AverageCurrent( ), Voltage( ) and Temperature( ) measurements are taken once per second, and the interface data set is updated. Decisions to change states are also made. This mode is exited by activating a different power mode.

Because the gauge consumes the most power in NORMAL mode, the Impedance Track™ algorithm minimizes the time the fuel gauge remains in this mode.

8.4.1.4 SLEEP Mode

SLEEP mode is entered automatically if the feature is enabled (Operation Configuration [SLEEP]) = 1) and AverageCurrent( ) is less than the programmable level Sleep Current (default = 10 mA). Once entry into SLEEP mode has been qualified, but before entering it, the bq27425 performs an ADC autocalibration to minimize offset.

During SLEEP mode, the bq27425 periodically takes data measurements and updates its data set. However, a majority of its time is spent in an idle condition.

The bq27425 exits SLEEP if any entry condition is broken, specifically when: AverageCurrent( ) rises above Sleep Current (default = 10 mA).

8.4.1.5 HIBERNATE Mode

HIBERNATE mode could be used when the system equipment needs to enter a very low-power state, and minimal gauge power consumption is required. This mode is ideal when a system equipment is set to its own HIBERNATE, SHUTDOWN, or OFF modes.

Before the fuel gauge can enter HIBERNATE mode, the system must set the [HIBERNATE] bit of the CONTROL_STATUS register. The gauge waits to enter HIBERNATE mode until it has taken a valid OCV measurement and the magnitude of the average cell current has fallen below Hibernate Current. The gauge can also enter HIBERNATE mode if the cell voltage falls below Hibernate Voltage. The gauge will remain in HIBERNATE mode until the system issues a direct I²C command to the gauge. I²C communication that is not directed to the gauge will only briefly wake it up and the gauge immediately returns to HIBERNATE mode.

It is the system’s responsibility to wake the bq27425 after it has gone into HIBERNATE mode and to prevent a charger from charging the battery before the [OCVTAKEN] bit is set which signals an OCV reading is taken. After waking, the gauge can proceed with the initialization of the battery information.

Table 3. Standard Commands

8.5.1.1 Control(): 0x00 and 0x01

Issuing a Control( ) command requires a subsequent 2-byte subcommand. These additional bytes specify the particular control function desired. The Control( ) command allows the system to control specific features of the bq27425 during normal operation and additional features when the bq27425 is in different access modes, as described in Table 4.

8.5.1.2 Temperature( ): 0x02 and 0x03

This read-/write-word function returns an unsigned integer value of the temperature in units of 0.1°K measured by the fuel gauge. If Op Config [TEMPS] bit = 0 (default), a read command will return the internal temperature sensor value and write command will be ignored. If Op Config [TEMPS] bit = 1, a write command sets the temperature to be used for gauging calculations while a read command returns to temperature previously written.

8.5.1.3 Voltage( ): 0x04 and 0x05

This read-only function returns an unsigned integer value of the measured cell-pack voltage in mV with a range of 0 to 6000 mV.

8.5.1.4 Flags( ): 0x06 and 0x07

This read-word function returns the contents of the gas gauge status register, depicting the current operating status.

8.5.1.5 NominalAvailableCapacity( ): 0x08 and 0x09

This read-only command pair returns the uncompensated (less than C/20 load) battery capacity remaining. Units are mAh.

8.5.1.6 FullAvailableCapacity( ): 0x0A and 0x0B

This read-only command pair returns the uncompensated (less than C/20 load) capacity of the battery when fully charged. Units are mAh. FullAvailableCapacity( ) is updated at regular intervals, as specified by the IT algorithm.

8.5.1.7 RemainingCapacity( ): 0x0C and 0x0D

This read-only command pair returns the compensated battery capacity remaining. Units are mAh.

8.5.1.8 FullChargeCapacity( ): 0x0E and 0x0F

This read-only command pair returns the compensated capacity of the battery when fully charged. Units are mAh. FullChargeCapacity( ) is updated at regular intervals, as specified by the IT algorithm.

8.5.1.9 AverageCurrent( ): 0x10 and 0x11

This read-only command pair returns a signed integer value that is the average current flow through the sense resistor. In NORMAL mode, it is updated once per second and is calculated by dividing the 1-second change in coulomb counter data by 1 second. Large current spikes of short duration will be averaged out in this measurement. Units are mA.

8.5.1.10 AveragePower( ): 0x18 and 0x19

This read-only function returns an signed integer value of the average power during battery charging and discharging. It is negative during discharge and positive during charge. A value of 0 indicates that the battery is not being discharged. The value is reported in units of mW.

8.5.1.11 StateOfCharge( ): 0x1C and 0x1D

This read-only function returns an unsigned integer value of the predicted remaining battery capacity expressed as a percentage of FullChargeCapacity( ), with a range of 0 to 100%.

8.5.1.12 IntTemperature( ): 0x1E and 0x1F

This read-only function returns an unsigned integer value of the internal temperature sensor in units of 0.1°K measured by the fuel gauge. If Op Config [TEMPS] = 0, this command will return the same value as Temperature( ).

8.5.1.13 StateOfHealth( ): 0x20 and 0x21

0x20 SOH percentage: this read-only function returns an unsigned integer value, expressed as a percentage of the ratio of predicted FCC(25°C, SOH LoadI) over the DesignCapacity(). The FCC(25°C, SOH LoadI) is the calculated full charge capacity at 25°C and the SOH LoadI which is programmed in factory (default = –400 mA). The range of the returned SOH percentage is 0x00 to 0x64, indicating 0 to 100% correspondingly.

0x21 SOH Status: this read-only function returns an unsigned integer value, indicating the status of the SOH percentage:

• 0x00: SOH not valid (initialization)
• 0x01: Instant SOH value ready
• 0x02: Initial SOH value ready
  • Calculation based on default Qmax
  • May not reflect SOH for currently inserted pack
• 0x03: SOH value ready
  • Calculation based on learned Qmax
  • Most accurate SOH for currently inserted pack following a Qmax update
• 0x04 through 0xFF: Reserved

8.5.1.14 OperationConfiguration( ): 0x3A and 0x3B

This read-only function returns the contents of the NVM Operation Configuration (Op Config) register and is most useful for system level debug to quickly determine device configuration.

8.5.1.15 DesignCapacity( ): 0x3C and 0x3D

This read-only function returns the value stored in Design Capacity and is expressed in mAh. This is intended to be the theoretical or nominal capacity of a new pack and is used as an input for the algorithm to scale the normalized resistance tables and for the calculation of StateOfHealth().

8.5.1.16 DebugX( ):

Several read-only functions such as Debug1( ), Debug2( ), Debug3( ) provide information useful for debug purposes. For factory use only.

Table 7. Extended Commands

8.5.2.1 OperationConfiguration( ): 0x3A and 0x3B

SEALED and UNSEALED Access: This command returns the Operation Configuration register setting.

8.5.2.2 DesignCapacity( ): 0x3C and 0x3D

SEALED and UNSEALED Access: This command returns the value is stored in Design Capacity and is expressed in mAh. This is intended to be the theoretical or nominal capacity of a new pack and is used as an input for the algorithm to scale the normalized resistance tables.

8.5.2.3 DataClass( ): 0x3E

UNSEALED Access: This command sets the data class to be accessed. The class to be accessed should be entered in hexadecimal.

SEALED Access: This command is not available in SEALED mode.

8.5.2.4 DataBlock( ): 0x3F

UNSEALED Access: This command sets the data block to be accessed. When 0x00 is written to BlockDataControl( ), DataBlock( ) holds the block number of the data to be read or written. Example: writing a 0x00 to DataBlock( ) specifies access to the first 32-byte block and a 0x01 specifies access to the second 32-byte block, and so on.

SEALED Access: Issuing a 0x01 instructs the BlockData( ) command to transfer the Manufacturer Info block.

8.5.2.5 BlockData( ): 0x40 through 0x5F

UNSEALED Access: This data block is the remainder of the 32-byte data block when accessing general block data.

SEALED Access: This data block is used to access the Manufacturer Info block. No other NVM or RAM data blocks are accessible in SEALED mode.

8.5.2.6 BlockDataChecksum( ): 0x60

UNSEALED Access: This byte contains the checksum on the 32 bytes of block data read or written. The least-significant byte of the sum of the data bytes written must be complemented ( [255 – x], for x being the least-significant byte) before being written to 0x60. For a block write, the correct complemented checksum must be written before the BlockData( ) will be transferred to NVM or RAM.

SEALED Access: This byte contains the checksum for the 8 bytes of the Manufacturer Info block.

8.5.2.7 BlockDataControl( ): 0x61

UNSEALED Access: This command is controls the data access mode. Writing 0x00 to this command enables BlockData( ) to access NVM and RAM.

SEALED Access: This command is not available in SEALED mode.

8.5.2.8 Reserved: 0x62 through 0x7F

8.5.3.1 Accessing Block Data

The fuel gauge contains both re-writable EEPROM non-volatile memory (NVM) and ROM-based data blocks. Upon device RESET, the ROM-based data blocks are copied to associated volatile RAM space to initialize default configuration and data constants to be used by the fuel gauging algorithm. Re-writable NVM-based data blocks contain information expected to change such as: calibration, customer data, and Impedance Track fuel gauging data tables. If the application requires a change to the NVM or RAM configuration data, the host can update the data blocks in CONFIG UPDATE mode. RAM-based data changes are temporary and must be applied by the host using CONFIG UPDATE mode after each device RESET; while changes to the NVM data blocks are permanent. The data blocks can be accessed in several different ways, depending on the access mode and what data is being accessed.

Commonly accessed data block locations, frequently read by a system, are conveniently accessed through specific instructions, already described in Extended Data Commands. These commands are available when the fuel gauge is either in UNSEALED or SEALED mode.

Most data block locations, however, are only accessible in UNSEALED mode by use of the evaluation software or by data block transfers. These locations should be optimized and/or fixed during the development and manufacture processes. Once established, the values generally remain unchanged during end-equipment operation.

To access data locations individually, the block containing the desired data NVM locations must be transferred to the command register locations, where they can be read to the system or changed directly. This is accomplished by sending the set-up command BlockDataControl( ) (0x61) with data 0x00. Up to 32 bytes of data can be read directly from the BlockData( ) (0x40 through 0x5F), externally altered, then rewritten to the BlockData( ) command space. Alternatively, specific locations can be read, altered, and rewritten if their corresponding offsets are used to index into the BlockData( ) command space. Finally, the data residing in the command space is transferred to the associated data block, once the correct checksum for the whole block is written to BlockDataChecksum( ) (0x60).

Occasionally, a data CLASS will be larger than the 32-byte block size. In this case, the DataBlock( ) command designates in which 32-byte block the desired locations reside. The correct command address is then given by 0x40 + offset modulo 32. For example, to access Sleep Current in the Gas Gauging class, the DataClass( ) is issued 82 (0x52) to set the class. Because the offset is 34, it resides in the second 32-byte block. Hence, DataBlock( ) is issued 0x01 to set the block offset, and the offset used to index into the BlockData( ) memory area is 0x40 + 34 modulo 32 = 0x40 + 2 = 0x40 + 2 = 0x42.

Reading and writing subclass data are block operations up to 32 bytes in length. If, during a write, the data length exceeds the maximum block size, then the data is ignored.

None of the data written to memory are bounded by the fuel gauge, the values are not rejected by the fuel gauge. Writing an incorrect value may result in hardware failure due to firmware program interpretation of the invalid data. The data written to NVM blocks is not persistent, so a power-on reset does resolve the fault.

Table 8. Data NVM Access

8.5.4.1 Sealing and Unsealing Data Blocks

The fuel gauge implements a key-access security scheme to transition from a SEALED state to the UNSEALED state. Devices are shipped from the factory in the UNSEALED state and should be SEALED before use in end-equipment. The Sealed to Unseal key can only be updated in the UNSEALED state.

To SEAL from UNSEALED: The host sends the SEALED subcommand 0x0020 to the Control( ) register. After receiving the SEALED subcommand, the CONTROL_STATUS [SS] bit is set within 2 seconds.

To UNSEAL from SEALED: Host sends the keys to the Control( ) register. The keys must be sent consecutively, with no other data written to Control( ).

The first word is Key 0 and the second word is Key 1. The order of the keys sent are Key 1 followed by Key 0. The order of the bytes for each key entered through the Control( ) command is the reverse of what is read from the part. For example, if the 4-byte Sealed to Unseal key is 0x56781234, key 1 is 0x1234 and key 0 is 0x5678. So, the host should write 0x3412 followed by 0x7856 to unseal the part. After receiving the correct key sequence the CONTROL_STATUS [SS] bit is cleared.

Table 9. Data Block Summary

8.5.7.1 I²C Interface

The fuel gauge supports the standard I²C read, incremental read, quick read, one-byte write, and incremental write functions. The 7-bit device address (ADDR) is the most significant 7 bits of the hex address and is fixed as 1010101. The first 8 bits of the I²C protocol are, therefore, 0xAA or 0xAB for write or read, respectively.

Figure 7. I²C Interface Read/Write

The quick read returns data at the address indicated by the address pointer. The address pointer, a register internal to the I²C communication engine, increments whenever data is acknowledged by the fuel gauge or the I²C master. “Quick writes” function in the same manner and are a convenient means of sending multiple bytes to consecutive command locations (such as two-byte commands that require two bytes of data).

The following command sequences are not supported:

Attempt to write a read-only address (NACK after data sent by master):

Figure 8. Attempt to Write a Read-Only Address

Attempt to read an address above 0x6B (NACK command):

Figure 9. Attempt to Read an Address Above 0x6B

8.5.7.2 I²C Time Out

The I²C engine releases both SDA and SCL if the I²C bus is held low for 2 seconds. If the fuel gauge is holding the lines, releasing them frees them for the master to drive the lines. If an external condition is holding either of the lines low, the I²C engine enters the low-power sleep mode.

8.5.7.3 I²C Command Waiting Time

To ensure proper operation at 400 kHz, a t_(BUF) ≥ 66 μs bus-free waiting time must be inserted between all packets addressed to the fuel gauge. In addition, if the SCL clock frequency (f_SCL) is > 100 kHz, use individual 1-byte write commands for proper data flow control. The following diagram shows the standard waiting time required between issuing the control subcommand the reading the status result. For read-write standard command, a minimum of 2 seconds is required to get the result updated. For read-only standard commands, there is no waiting time required, but the host must not issue any standard command more than two times per second. Otherwise, the gauge could result in a reset issue due to the expiration of the watchdog timer.

Figure 10. I²C Command Waiting Time

8.5.7.4 I²C Clock Stretching

A clock stretch can occur during all modes of fuel gauge operation. In SLEEP and HIBERNATE modes, a short clock stretch occurs on all I²C traffic as the device must wake up to process the packet. In the other modes (INITIALIZATION, NORMAL) clock stretching only occurs for packets addressed for the fuel gauge. The majority of clock stretch periods are small as the I²C interface performs normal data flow control. However, less frequent yet more significant clock stretch periods may occur as blocks of NVM are updated. The following table summarizes the approximate clock stretch duration for various fuel gauge operating conditions.

Table 11. Op Config Register Definition