SLUA475 November 2016 BQ2060A , BQ20Z80 , BQ40Z50-R1 , BQ40Z50-R2 , BQ40Z60 , BQ78350-R1 , BQ78350-R1A
1.2.1 Clock Stretching
Figure 3. SMBus Clock Stretch Clock stretching is a simple way for the slave to indicate to the host that it is busy (see Figure 3). Any time the clock is low in the packet, the slave has the right to grab the clock and hold it low as long as required; however, the bit must not cause a packet timeout (25 ms).
The entire packet must not be longer than 25 ms, which includes the clock stretch. TI fuel gauges usually only clock stretch before or after the ACK or NACK bits.