Data Sheet
ICM-20948
Document Number: DS-000189 Page 81 of 89
Revision: 1.3
14 USE NOTES
14.1 GYROSCOPE MODE TRANSITION
When gyroscope is transitioning from low-power to low-noise mode, several unsettled output samples will be
observed at the gyroscope output due to filter switching and settling. The number of unsettled gyroscope output
samples depends on the filter and ODR settings.
14.2 POWER MANAGEMENT 1 REGISTER SETTING
CLKSEL[2:0] has to be set to 001 to achieve the datasheet performance.
14.3 DMP MEMORY ACCESS
Reading/writing DMP memory and FIFO through I
2
C in a multithreaded environment can cause wrong data being read.
To avoid the issue, one may use SPI instead of I
2
C, or use I
2
C with mutexes.
14.4 TIME BASE CORRECTION
The system clock frequency at room temperature in gyroscope mode and 6-Axis mode varies from part to part, and
the clock rates specified in datasheet are the nominal values. The percentage of frequency deviation from the nominal
values for each part is logged in register TIMEBASE_CORRECTION_PLL, and the range of the code is ±10% with each
LSB representing a step of 0.079%. For example, if on one part TIMEBASE_CORRECTION_PLL = 0x0C = d’12, it means
the clock frequency in gyroscope mode and 6-Axis mode is ~0.94% faster than the nominal value.
When operating in accelerometer-only mode, the system clock frequency at room temperature is the nominal
frequency over parts, and it is independent of the value stored in TIMEBASE_CORRECTION_PLL register.
14.5 I
2
C MASTER CLOCK FREQUENCY
I
2
C master clock frequency can be set by register I2C_MST_CLK as shown in Table 23. Due to temperature variation
and part to part variation of system clock frequency in different power modes, I2C_MST_CLK should be set such that
in all conditions the clock frequency will not exceed what a slave device can support. To achieve a targeted clock
frequency of 400 kHz, MAX, it is recommended to set I2C_MST_CLK = 7 (345.6 kHz / 46.67% duty cycle).
I2C_MST_CLK
NOMINAL CLK
FREQUENCY [KHZ]
DUTY CYCLE
0 370.29 50.00%
1 - -
2 370.29 50.00%
3 432.00 50.00%
4 370.29 42.86%
5 370.29 50.00%
6 345.60 40.00%
7 345.60 46.67%
8 304.94 47.06%
9 432.00 50.00%
10 432.00 41.67%
11 432.00 41.67%
12 471.27 45.45%
13 432.00 50.00%