BQ27000 Datasheet, PDF (25/29 Pages) Texas Instruments – SINGLE CELL Li-Ion AND Li-Pol BATTERY GAS GAUGE IC FOR PORTABLE APPLICATIONS (bqJUNIOR)

bq27000, bq27200
www.ti.com
SLUS556B – SEPTEMBER 2004 – REVISED NOVEMBER 2004
If a communication timeout occurs (for example, if the host waits longer than T_(RSPS) for the bq27000 to respond)
or if this is the first access command, then a BREAK should be sent by the host. The host may then resend the
command. The bq27000 detects a BREAK when the HDQ pin is driven to a logic-low state for a time T_(B) or
greater. The HDQ pin then returns to its normal ready-high logic state for a time T_(BR).The bq27000 is then ready
for a command from the host processor.
The return-to-one data-bit frame consists of three distinct sections:
1. The first section starts the transmission by either the host or the bq27000 taking the HDQ pin to a logic-low
state for a period equal to T_(HW1) or T_(DW1).
2. The next section is the actual data transmission, where the data should be valid for T_(HW0)- T_(HW1) or T_(DW0)-
T_(DW1).
3. The final section stops the transmission by returning the HDQ pin to a logic-high state and holding it high
until the time from bit start to bit end is equal to T_(CYCH) or T_(CYCD).
The HDQ line can remain high for an indefinite period of time between each bit of address or between each bit of
data on a write cycle. After the last bit of address is sent on a read cycle, the bq27000 starts outputting the data
after T_(RSPS) with timing as specified. The serial communication timing specification and illustration sections give
the timings for data and break communication. Communication with the bq27000 always occurs with the
least-significant bit being transmitted first.
Plugging in the battery pack can be seen as the start of a communication due to contact bounce. It is
recommended that each communication or string of communications be preceded by a break to reset the HDQ
engine.
Command byte
The Command byte of the bqJUNIOR consists of eight contiguous valid command bits. The command byte
contains two fields: W/R Command and address. The Command byte values are shown as follows:
7
6
5
4
3
2
1
0
W/R
AD6
AD5
AD4
AD3
AD2
AD1
AD0
W/R
Indicates whether the command bytes is a read or write command. A 1 indicates a write command
and that the following eight bits should be written to the register specified by the address field of the
Command byte, whereas a 0 indicates that the command is a read. On a read command, the
bqJUNIOR outputs the requested register contents specified by the address field portion of the
Command byte.
AD6-AD0 The seven bits labeled AD6—AD0 containing the address portion of the register to be accessed.
Reading 16-bit Registers
Because 16-bit values are read only 8 bits at a time with the HDQ interface, it is possible that the device can
update the register value between the time the host reads the first and second bytes. To prevent any system
issues, any 16-bit values read by the host should be read with the following procedure.
1. Read high byte (H0).
2. Read low byte (L0).
3. Read high byte (H1).
4. If H1=H0, then valid result is H0, L0.
5. Otherwise, read low byte (L1) and valid result is H1, L1.
This procedure assumes that the 3 or 4 reads are made more quickly than the update rate of the value. The
maximum update rate of any value in the bq27000/27200 is 1.28 seconds.
Communicating with the bq27200 (I²C interface)
The bq27200 supports the standard I²C read, incremental read, quick read, and one byte write 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. (S = Start, Sr = Repeated Start, A =
Acknowledge, N = No Acknowledge, and P = Stop)
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