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DRV5033: DRV5033

Part Number: DRV5033
Other Parts Discussed in Thread: , DRV5055

We are using the DRV5033 in TO92 case hall sensor on a project, the problem is that each sensor switches at a different height from the magnet  (within a 5mm difference). We have set up a jig so that the only variable is the hall sensor, we have the same voltage 3 volt, magnet is a Dia 4x8mm (+/- 83 Gauss) the magnet is 10mm away from the magnet. How do we get that all the sensors switch at the same height (within 0,3mm of each other) 

  • Arnold,

    Thanks for choosing the TI forums. To be able to help here, I have a few followup questions.

    - Can you share the grade of the magnet you are using here?

    - Can you share which version of the DRV5033 you are using?

    - Is my understanding correct you are bringing the north face of the cylinder magnet down to the face of the TO-92 package to activate the device?


  • Hi Carolus 

    Thank you for the reply 

    - magnet is a N38 NI Neodymium or NI plated rear earth magnet Dia 4mm x 8mm long 

    - we have tried the DRV5033AJQLPGM and the DRV5033-Q1

    - We have tried bringing the face of the magnet past the face of the sensor and we have tried bringing the face perpendicular to the face of sensor both with the same effect. 

    Are these sensors built to switch in same position ? what would the tolerances be from sensor to sensor ? 

  • Arnold,

    Thanks for the information. There are a few things here that you need to take into consideration in terms of tolerance where your trip point will occur:

    1. Magnets are not a one stop shop, and neodymium grades, ferrites, etc. all fall on a distribution themselves. For example, looking at the standard N38 type magnet, this material will typically exhibit anywhere from 12.2-12.6 kGs. This means that the magnet will produce a slightly varying strength from magnet to magnet, and will affect your trip distance.

    2. The main distribution you need to examine from the sensor perspective are the operating and release points, or BOP and BRP, of the sensor. If we look at the datasheet for the DRV5033:

    For the AJ version of this device, the operating point, while typically 6.9mT, this can range from 3mT to 12 mT. If we examine the magnet traveling head on case using the magnetic field calculator (located in the DRV5033 product folder. A useful "B strength at X distance" calculator can be found in the DRV5055 product folder as well), we see that these points for an N38 4mmDx8mmH magnet occur at 15.2mm and 8.5mm, respectively. This means that over the full potential range of operating points as it varies from part to part, there is a possible distance delta of 6.7mm in your current design of where the Hall sensor would actually trip. 

    in general, the curve of the magnet's magnetic strength is a classic y = 1/x curve. When working with very strong magnets and very high sensitivity sensors, you are operating on the flat portion of the "L" curve, and these distributions tend to be well sparsed out due to the flat nature of the curve. When working with lesser sensitivities and weaker magnets, you are forced to bring the magnet closer to the part which operates on the leg of the L curve, where even a large change in distribution results in a very small delta of distance traveled. 

    To pull this in, I would start by looking into a weaker magnet, which would need to get closer to the sensor for it to trip. For example, if I use the same form factor as the magnet you are using above, and change the grade of the magnet to a typical ferrite magnet (typical strength is ~4kGs), these points now correlate to 9.5mm and 5mm, shrinking the above delta to 4.5mm. Decreasing the size of the magnet is also an option to help tighten this up.

    By the same token, you could also look to less sensitive sensors as well. Do you absolutely need to be in a TO-92 package here? If you can use a SOT-23 and bring the magnet down onto it, you may want to check out DRV5032ZE. If you need to use the TO-92 package, you could check  out the DRV5023BI, which has min/max BOP of 6/24 mT. With these points, for a 4mmDx8mmH ferrite magnet, your points would reduce even further to 3.45mm and 6.95mm, for a total distance delta of 3.5mm. Again, reducing the size of the magnet would continue to reduce this further.