DRV5055: Sensing distance

Hello Sindhuja,

Thank you for using the TI forum. In general, getting a larger/stronger magnet will allow you to sense the magnet at a farther distance from the sensor. You can use magnetic calculators, such as the one found on the DRV5012 product page (www.ti.com/.../DRV5012) to determine the magnetic flux density at a given distance from the sensor for a specified magnet. Then use the gain value (linear sensors) or sensor trip point (switches and latches) of the Hall device to see if that flux density will be enough for your application. Also, using a sensor with a higher gain value (or a lower trip point) will detect weaker magnetic fields. I have a few other suggestions for you based on what is important to you in your design:

1) If you need a linear output sensor (to determine how close the magnet is within the 40-50 mm) and:
a. You need both poles of the magnet then you may want to use the DRV5055A1. This has a gain of 100 mV/mT. You will still need a fairly large/strong magnet for this to work well from 40-50 mm.
b. You only need one pole of the magnet then you may want to use the DRV5056A1. This has a gain of 200 mV/mT. This would allow a smaller/weaker magnet than option (1), but it would still have to be a fairly strong magnet.

2) If you only need a switch to detect if the magnet is present and:
a. You don’t care if it is a north or south pole that trips the sensor, then you could use the DRV5033FA. This sensor has a trip point of ±3.5 mT (±6.8 mT MAX) and a release point of ±2 mT (±0.5 mT MIN). (You can use the calculator to see what types of magnet produce that field at your preferred distance).
b. You need to know if the magnet is a north or south pole, then you could use the DRV5032DU. This sensor has a trip point of ±2.5 mT (±3.9 mT MAX) and a release point of ±1.8 mT (±0.9 mT MIN), and has two outputs so that you can tell if the north or south pole tripped the sensor. (You can use the calculator to see what types of magnet produce that field at your preferred distance; slightly smaller magnet needed the previous option).

3) If you are doing some kind of rotary encoding or other design where a latch device is useful, then you may want to use the DRV5015A1. This sensor has a trip and release point of ±0.7 mT (±2 mT MAX/MIN) (released by the opposite pole). This option allows you the smallest magnet of the options I have given you, but is application specific.

A list of our Hall Effect Devices, along with some other recourse can be found at this forum post: e2e.ti.com/.../2664186

Hello Sindhuja,

I believe that at a distance doubling up the magnets would have a similar effect to doubling the thickness of the magnet (as long as the magnets are the same orientation). If you would like to simulate your design to see more accurately how this would affect the magnetic field, then you could use a free 2D simulation program such as FEMM (www.femm.info/.../HomePage). Although, It may be easier to predict the outcome if you just use one magnet. The forum post I referenced above has a list of some common magnet suppliers, and specifically k&j magnetics (https://www.kjmagnetics.com/) has a pretty good variety of magnet sizes.