BQ27741-G1_14 Datasheet, PDF (17/39 Pages) Texas Instruments – Single Cell Li-Ion Battery Fuel Gauge with Integrated Protection

www.ti.com
NOTE
Formatting Conventions in This Document:
Commands: italics with parentheses and no breaking spaces, for example,
RemainingCapacity( ).
Data Flash: italics, bold, and breaking spaces, for example, Design Capacity.
Register Bits and Flags: brackets only, for example, [TDA]
Data Flash Bits: italic and bold, for example, [XYZ1]
Modes and states: ALL CAPITALS, for example, UNSEALED mode.
bq27741-G1
SLUSBF2 – JULY 2013
Communications
HDQ Single-Pin Serial Interface
The HDQ interface is an asynchronous return-to-one protocol where a processor sends the command code to
the fuel gauge. With HDQ, the least significant bit (LSB) of a data byte (command) or word (data) is transmitted
first. The DATA signal on pin 12 is open-drain and requires an external pullup resistor. The 8-bit command code
consists of two fields: the 7-bit HDQ command code (bits 0 through 6) and the 1-bit RW field (MSB bit 7). The
RW field directs the fuel gauge either to:
• Store the next 8 bits of data to a specified register, or
• Output 8 bits of data from the specified register
The HDQ peripheral can transmit and receive data as either an HDQ master or slave.
HDQ serial communication is normally initiated by the host processor sending a break command to the fuel
gauge. A break is detected when the DATA pin is driven to a logic low state for a time t_(B) or greater. The DATA
pin then is returned to its normal ready logic high state for a time t_(BR). The fuel gauge is now ready to receive
information from the host processor.
The fuel gauge is shipped in the I²C mode. TI provides tools to enable the HDQ peripheral.
HDQ Host Interruption
The default fuel gauge behaves as an HDQ slave-only device. If the HDQ interrupt function is enabled, the fuel
gauge is capable of mastering and also communicating to a HDQ device. There is no mechanism for negotiating
which is to function as the HDQ master and care must be taken to avoid message collisions. The interrupt is
signaled to the host processor with the fuel gauge mastering an HDQ message. This message is a fixed
message that signals the interrupt condition. The message itself is 0x80 (slave write to register 0x00) with no
data byte being sent as the command is not intended to convey any status of the interrupt condition. The HDQ
interrupt function is not public and needs to be enabled by command.
When the SET_HDQINTEN subcommand is received, the fuel gauge detects any of the interrupt conditions and
asserts the interrupt at one-second intervals until either:
• The CLEAR_HDQINTEN subcommand is received, or
• The number of tries for interrupting the host has exceeded a predetermined limit. After the interrupt event,
interrupts are automatically disabled. To re-enable interrupts, SET_HDQINTEN needs to be sent.
Low Battery Capacity
This feature works identically to SOC1. It uses the same data flash entries as SOC1 and triggers interrupts as
long as SOC1 = 1 and HDQIntEN = 1.
Temperature
This feature triggers an interrupt based on the OTC (Overtemperature in Charge) or OTD (Overtemperature in
Discharge) condition being met. It uses the same data flash entries as OTC or OTD and triggers interrupts as
long as either the OTD or OTC condition is met and HDQIntEN = 1. (See detail in HDQ Host Interruption.)
Copyright © 2013, Texas Instruments Incorporated
Product Folder Links: bq27741-G1
Submit Documentation Feedback
17