BQ27421-G1 Datasheet, PDF (13/20 Pages) Texas Instruments – System-Side Impedance Track™ Fuel Gauge With Integrated Sense Resistor

bq27421-G1
www.ti.com
SLUSB85 – MAY 2013
I²C Command Waiting Time
To ensure proper operation at 400 kHz, a t_(BUF) ≥ 66 μs bus-free waiting time must be inserted between all
packets addressed to the bq27421-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 must not issue any standard command 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
I²C Clock Stretching
A clock stretch can occur during all modes of fuel gauge operation. In SLEEP and HIBERNATE modes, a short ≤
100 µs clock stretch occurs on all I²C traffic as the device must wake-up to process the packet. In the other
modes ( INITIALIZATION , NORMAL) a ≤ 4 ms clock stretching period may occur within packets addressed for
the fuel gauge as the I²C interface performs normal data flow control.
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