The TMAG6181-Q1 has a rotation tracking feature to track high-speed rotations at low current consumption to save power. This feature lets the device decrease the sleep time when magnetic field rotations are detected, and enables the device to track the higher speed and acceleration events. When the turns counter is enabled using the TURNS pin, the rotation tracking feature is also enabled. This feature is enabled in both the active-turns mode and the low-power mode (see Device Functional Modes).

In active mode, when the turns counter is enabled, the Hall sensor signals are monitored approximately every 1.6ms. But when a rotation is detected, the period between the next wake-up event is reduced by 1/8th to 0.2ms. If no rotation change is detected for four consecutive periods, then the sleep time is increased to 0.4ms. If new rotations are detected, then the tracking algorithm goes to 0.2ms and the counter for the four consecutive periods is reset. If no rotations are detected in next four consecutive periods, then the sleep time is doubled again to 0.8ms and then eventually back to 1.6ms if no more rotations are detected. After reaching this default value of 1.6ms, the rotation tracking feature allows theTMAG6181-Q1 to continue sampling at this fixed period until new rotations are detected.

In low-power mode, when the turns counter is enabled, the Hall sensor signals are monitored approximately every 25.6ms. But when a rotation is detected, the period between the next wake-up event is reduced by 1/16th to 1.6ms. If no rotation change is detected for four consecutive periods, then the sleep time is increased to 3.2ms. If new rotations are detected, then the tracking algorithm goes to 1.6ms and the counter for the four consecutive periods is reset. If no rotations are detected in the next four consecutive periods, then the sleep time is doubled again to 6.4ms and then to 12.8ms after the next four cycles. After reaching the default value of 25.6ms, the rotation tracking feature allows the TMAG6181-Q1 to continue sampling at this fixed period until new rotations are detected. Figure 6-17 shows the rotation tracking feature during low-power mode.

Use Equation 16 to calculate the maximum angle travel, θ, for a rotating magnetic field.

where,

• t is the field travel time
• v is the velocity of the moving field in rpm
• a is the acceleration of the moving field in rpm/second

The turns counter has an angle resolution of 90°. The turns counter can successfully track the rotations if the counter ensures the state transitions (as shown in Figure 6-13) and does not jump any states. At an acceleration of 6000rpm/sec, the rotation tracking feature enables the device to track up to 8000rpm during low-power mode and in active-turns mode, and enables at track up to 60000rpm.

Table 6-1 shows the trade-off between maximum speed (in rpm) that can be tracked by the turns counter and the current consumption in active mode.

Table 6-2 shows the trade-off between maximum speed (in rpm) that can be tracked by the turns counter and the current consumption in low-power mode