BQ27742-G1 Datasheet, PDF (24/46 Pages) Texas Instruments – Single-Cell Li-Ion Battery Fuel Gauge with Programmable Hardware Protection

bq27742-G1
SLUSBV9C – MARCH 2014 – REVISED FEBRUARY 2016
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Battery Parameter Measurements (continued)
7.5.5 Temperature
The fuel gauge external temperature sensing is optimized with the use of a high-accuracy negative temperature
coefficient (NTC) thermistor with R25 = 10 kΩ ± 1% and B25/85 = 3435 kΩ ± 1% (such as Semitec 103AT for
measurement). The fuel gauge can also be configured to use its internal temperature sensor. The fuel gauge
uses temperature to monitor the battery-pack environment, which is used for fuel gauging and cell protection
functionality.
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.
7.6 Communications
7.6.1 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.
7.6.2 I²C Interface
The fuel gauge 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.
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