TMAG5273: TMAG5273A1QDBVR

Hello Nirmith,

Thanks for posting to the sensing forum! Is there a specific reason why TMAG5273 was chosen for measuring the RPM of a motor? Typically, for RPM measurements digital hall latches or switches are used. As the motor rotates you will obtain a square wave, obtaining the electrical frequency of the motor lets you mathematically convert the electrical frequency to the motors RPM. I am just curious if the plan is to use the alert pin on the TMAG5273 in order to make the measurement or if another method was going to be used.

The frequency bandwidth of TMAG5273 isn't specifically published because it mainly depends on your setup of the device. You can see the spec under section 6.11 Power up and Conversion Time. If only one channel is enabled then the conversion time is 50us then 20kHz, but once other channels are added then conversion for each subsequent channel is 25us.

I hope this helps!

Best,

Isaac

Hey Nirmith,

Thanks for the info. My suggestions would be to go with a latch, either DRV5011 (smaller package in case it makes your design easier) or DRV5013. If you are getting about +/-60mT from the permanent magnets on the motor then you shouldn't have any problems finding a sensitivity suitable for your motor.

When using the electrical frequency from a digital latch you can use the following formula to calculate the RPM of the motor: 

RPM= (60*Electrical frequency)/pole pairs

Electrical frequency being the measured frequency from your latch, and pole pairs is the amount of pole pairs in the rotor.

Best,

Isaac

Hello Nirmith,

It sounds like you are using the best option for your application at the moment. Another option you can do is have TMAG5273 set up to generate an interrupt INT pin when the threshold has crossed a specific value. This will generate the square wave that is typically used to obtain the electrical frequency. Look at section 7.3.3 in the datasheet for more information on how the interrupt functions works. The formula would change slightly since you would be getting twice the amount of transitions since it would function as a switch.

Best,

Isaac

Hey Nirmith,

When INT_MODE is set on the TMAG5273, it can be setup to create an interrupt either on the SCL pin or through the INT pin. I find it easier to interrupt through the INT pin but this also depends on how many GPIO's you have available on your MCU.

The interrupt occurs when the magnetic field goes above your programmed threshold, this is what I mean by a specific value. The threshold value is chosen by you and is configured using the X_THR_CONFIG, Y_THR_CONFIG, or Z_THR_CONFIG registers. The direction you choose mainly depends on where you are sensing the rotors polarity transitions. Essentially, you would be setting up TMAG5273 to act as a switch.

If you choose to go through the interrupt function, then it might not be completely necessary to read the magnetic data for that channel since you should be seeing the INT pin toggling when the motor is running. The INT pin would be connected to a microcontrollers GPIO pin where you can use a timer to time the frequency of the falling edges of the input (falling edges since this is an active low pin).

I made a mistake earlier and the calculation for RPM would remain the same, RPM= (60*Electrical frequency)/pole pairs. Since we are only timing the edges it would not make a difference to the formula. This would all be done inside the MCU. Just keep in mind that you still have to pay attention to the conversion time and we recommend that the conversion time is more than 2 times the max RPM you are expecting from the motor.

As far as code goes I am not sure if I have anything to provide. Did you just need code to configure the TMAG5273 into the interrupt mode? Or were you looking for something else?

Best,

Isaac

Hi Isaac 

Ya sure Thank you for helping me out.

Regards 

Nirmith