BQ27620-G1 Datasheet, PDF (38/45 Pages) Texas Instruments – System-Side Impedance Track™ Fuel Gauge

bq27620-G1
SLUSAE3 – OCTOBER 2012
www.ti.com
7.3 I²C Command Waiting Time
To ensure proper operation at 400 kHz, a t_(BUF) ≥ 66 μs bus free waiting time should be inserted between
all packets addressed to the bq27620-G1 . 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 should not issue all standard
commands more than two times per second. Otherwise, the gauge could result in a reset issue due to the
expiration of the watchdog timer.
S ADDR [6:0] 0 A CMD [7:0] A DATA [7:0] A P 66ms
S ADDR [6:0] 0 A CMD [7:0] A DATA [7:0] A P 66ms
S ADDR [6:0] 0 A CMD [7:0] A Sr ADDR [6:0] 1 A DATA [7:0] A DATA [7:0]
Waiting time inserted between two 1-byte write packets for a subcommand and reading results
(required for 100 kHz < f_SCL £ 400 kHz)
NP
66ms
S ADDR [6:0] 0 A CMD [7:0] A DATA [7:0] A DATA [7:0] A P 66ms
S ADDR [6:0] 0 A CMD [7:0] A Sr ADDR [6:0] 1 A DATA [7:0] A DATA [7:0] N P
Waiting time inserted between incremental 2-byte write packet for a subcommand and reading results
(acceptable for f_SCL £ 100 kHz)
66ms
S ADDR [6:0] 0 A CMD [7:0] A Sr ADDR [6:0] 1 A DATA [7:0] A DATA [7:0] A
DATA [7:0] A DATA [7:0] N P 66ms
Waiting time inserted after incremental read
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 will occur on all I²C traffic as the device must wake-up to process the packet. In the
other modes ( BAT INSERT CHECK , NORMAL) clock stretching will only occur 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 Data
Flash are updated. The following table summarizes the approximate clock stretch duration for various fuel
gauge operating conditions.
Gauging Mode
SLEEP
HIBERNATE
BAT INSERT
CHECK
NORMAL
Operating Condition / Comment
Clock stretch occurs at the beginning of all traffic as the device wakes up.
Clock stretch occurs within the packet for flow control. (after a start bit, ACK or first data bit)
Normal Ra table Data Flash updates.
Data Flash block writes.
Restored Data Flash block write after loss of power.
End of discharge Ra table Data Flash update.
Approximate
Duration
≤ 4 ms
≤ 4 ms
24 ms
72 ms
116 ms
144 ms
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COMMUNICATIONS
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