The TMAG6181-Q1 features an integrated 11-bit turns counter that can be used to keep track of rotation counts in different modes of operation (see Device Functional Modes). Figure 7-2 shows the typical application diagram when the turns counter is used in the system. The turns counter can be initiated and reset using the open-drain TURNS pin.

The turns counter uses the integrated X and Y Hall sensors to detect the rotation. The outputs from the Hall sensors are sampled at an interval of t_{tc_update} to update the turns counter. The turns counter can detect a change in the applied magnetic field at a resolution of 90° with a range of 360°. The turns counter also keeps track of direction information. The counter is incremented if the applied field is rotated clockwise and decremented if the field is rotated counter-clockwise. Figure 6-13 shows the counter operation based on the rotation of the input magnetic field.

Figure 6-13 Turns Counter Operation

The turns counter information is sent using the TURNS pin in a Pulse Width Modulation (PWM) format. Figure 6-14 shows the PWM duty cycle variation based on the turns counter value. The typical pulse-width modulation (PWM) carrier frequency is 2.5kHz. When the counter value is 0, the TURNS pin outputs a 50% duty cycle.

Figure 6-14 Turns Counter PWM Output on TURNS Pin

Figure 6-15 shows the timing diagram to enable the turns counter in active mode. When the part powers up, the turns counter is not enabled by default. The turns counter can be enabled by holding the TURNS pin low, for at least t_{tc_start}. When the TURNS pin is released, the pin turns into the output mode and sends out the PWM pulses corresponding to the internal turns counter after a time delay of t_{tc_delay}, as provided in the Specifications. To reset the counter and disable the output on TURNS pin, TURNS is pulled low for at least t > t_{tc_reset}. When the turns counter is enabled in the active mode, the internal wake-up oscillator is used to enable the Hall sensor signal path at regular intervals to update the turns counter information. This allows the device to keep the turns counter feature on at a lower power consumption overhead.

Figure 6-15 Timing Diagram Showing the Turns Counter Operation in Active Mode

Figure 6-16 shows the timing diagram of the turns counter operation in low-power mode. The part can be placed in a low-power, duty-cycled state if the turns counter is enabled. During this low-power state, an internal wake-up oscillator is used to wake up the device at regular intervals, t_sleep. When the part wakes up, the integrated Hall sensor signals are monitored for a rotation, and the turns counter information is updated. The TURNS pin does not output the PWM pulses during this low-power state. When the part is moved into an active state from the low-power state, the PWM pulses corresponding to the turns counter information saved during the low-power state is sent out to the microcontroller.

Figure 6-16 Timing Diagram Showing the Turns Counter Operation in Low-Power Mode