7.1 Overview

The bq34110 device incorporates multiple capabilities to provide detailed and sophisticated information on single-cell and multi-cell battery packs. Several different battery chemistries are supported, including Li-Ion, LiFePO4, lead-acid (PbA), Nickel Metal Hydride (NiMH), and Nickel Cadmium (NiCd). The device integrates a gas gauge for monitoring battery charge level, an End-Of-Service (EOS) Determination function to evaluate when a battery is nearing the end of its usable life, a specialized WHr Charge Termination function to enable battery charging to a targeted energy capacity, a charge control scheme using direct pin control, SHA-1/HMAC-based authentication, and lifetime data logging functionality.

7.2 Functional Block Diagram

7.3 Feature Description

The bq34110 gas gauge uses Compensated End-of-Discharge Voltage (CEDV) technology to accurately predict the battery capacity and other operational characteristics of the battery, and can be interrogated by a host processor to provide cell information, such as remaining capacity, full charge capacity, and average current.

The integrated End-Of-Service (EOS) Determination function is specifically intended for applications where the battery is rarely discharged, such as in uninterruptible power supplies (UPS), enterprise server backup systems, and telecommunications backup modules. In such systems, the battery may remain in a fully (or near-fully) charged state for much of its lifetime, with it rarely or never undergoing a significant discharge. If the health of the battery in such a system is not monitored regularly, then it may degrade beyond the level required for a system backup/discharge event, and thus fail precisely at the time when it is needed most.

The EOS Determination function monitors the health of the battery through the use of infrequent Learning Phases, which involves a controlled discharge of ~1% capacity, and provides an alert to the system when the battery is approaching the end of its usable service. By coordinating battery charging with the Learning Phases, the battery capacity available to the system can be maintained above a preselected level to avoid compromising the ability for the battery to support a system discharge event.

The bq34110 device can support multi-cell battery configurations with maximum voltage up to 65 V through the use of external and internal resistive divider networks to reduce the voltage to an acceptable range for the device’s integrated ADC. These resistive dividers are actively controlled to avoid unnecessary power dissipation when not needed. The device integrates an internal temperature sensor as well as support for an external NTC thermistor, such as a Semitec 103AT or Mitsubishi BN35-3H103FB-50.

The battery current is monitored by measuring the voltage across a series resistor, R_SENSE, which is placed in series with the battery pack and has a typical value of 5 mΩ to 20 mΩ. The bq34110 device integrates two ADCs, one of which is dedicated to current measurement, and the second used for measurement of several other parameters, including temperature and voltage.

Communication with the device is provided through an I²C interface, supporting rates up to 400 kHz. Dual ALERT pins are provided with programmable configuration, which enables them to be used for such functions as a host interrupt/alert or controlling the battery charger.

To minimize power consumption, the bq34110 gauge has several power modes: NORMAL, SNOOZE, and SLEEP, which are under register or algorithm control. In addition, a separate chip enable (CE) pin is provided to control the internal LDO, which powers the bq34110 internal circuitry, and can put the device into SHUTDOWN mode.

Information is accessed through a series of commands called Data Commands, which are indicated by the general format Command(). These commands are used to read and write information in the bq34110 device’s control and status registers, as well as its data flash locations.

Commands are sent from the host to the bq34110 device via I²C and can be executed during application development, pack manufacture, or end-equipment operation. Cell information is stored in the bq34110 device in non-volatile flash memory. Many of the data flash locations are accessible during application development and pack manufacture. They cannot, generally, be accessed directly during end-equipment operation. Access to these locations is achieved by using the bq34110 device’s companion evaluation software, through individual commands, or through a sequence of data flash access commands. To access a desired data flash location, the correct data flash subclass and offset must be known.

The bq34110 device provides 32 bytes of user-programmable data flash memory. This data space is accessed through a data flash interface. For specifics on accessing the data flash, see the bq34110 Technical Reference Manual (SLUUBF7).

A SHA-1/HMAC-based battery pack authentication feature is also implemented on the bq34110 device. When the device is in UNSEALED mode, authentication keys can be (re)assigned. A scratch pad area is used to receive challenge information from a host and to export SHA-1/HMAC encrypted responses. For more information on authentication, see the bq34110 Technical Reference Manual (SLUUBF7).

7.3.1 Communications

7.3.1.1 I²C Interface

The bq34110 device supports the standard I²C read, incremental read, one-byte write quick read, and functions. The 7-bit device address (ADDR) is the most significant 7 bits of the hex address and is fixed as 1010101. The 8-bit device address is therefore 0xAA or 0xAB for write or read, respectively.

Figure 6. Supported I²C formats: (a) 1-byte write, (b) quick read, (c) 1 byte-read, and (d) incremental read (S = Start, Sr = Repeated Start, A = Acknowledge, N = No Acknowledge, and P = Stop).

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 device 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 2-byte commands that require two bytes of data).

Figure 7. Attempt to Write a Read-Only Address (Nack After Data Sent By Master)

Figure 8. Attempt to Read an Address Above 0x7F (NACK Command)

Figure 9. Attempt at Incremental Writes (Nack All Extra Data Bytes Sent)

Figure 10. Incremental Read at the Maximum Allowed Read Address

7.3.1.2 I²C Time Out

The I²C engine releases both SDA and SCL if the I²C bus is held low for a time programmed in data flash. If the device were holding the lines, releasing them frees the master to drive the lines.

Detailed examples of I²C transactions accessing gauge data can be found in the Using I²C Communication with the bq275xx Series of Fuel Gauges Application Report (SLUA467).

7.4 Device Functional Modes

The bq34110 device has four functional power modes: NORMAL, SNOOZE, SLEEP, and SHUTDOWN, based on firmware and/or host control.

• In NORMAL mode, the device is fully powered and can execute any allowable task.
• In SNOOZE mode, the device periodically wakes to take data measurements and updates the data set, after which it then returns directly to SNOOZE.
• In SLEEP mode, the device maintains the low-frequency oscillator but turns off the high-frequency oscillator and exists in a reduced-power state, periodically taking measurements and performing calculations.
• In SHUTDOWN mode, the device is fully powered down and can only be awakened using the chip enable (CE) pin.