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MLX90217
Cam Sensor
 Download MLX90217 Datasheet (PDF)
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MLX90217 General Description
The MLX90217 is a self adjusting digital output rotary position gear tooth sensor designed for use in automotive camshaft sensing as well as other speed sensing applications. It is designed to be used with a bias magnet south facing the back (non-marked) side of the IC. The device has an open collector output which is short circuit protected.
The MLX90217 is a sophisticated IC featuring an on-chip 10-bit A/D Converter and logic that acts as a digital sample and hold circuit. A separate 4-bit A/D converter provides a fixed hysteresis. The 90217 does not have a chopper delay. The 90217 uses a single Hall plate which is immune to rotary alignment problems. The bias magnet can be from 50 to 400mT.
As the signal is sampled, the logic recognizes an increasing or decreasing flux density. The output will turn on (BOP) after the flux has reached its peak and decreased by an amount equal to the hysteresis. Similarly the output will turn off (BOP) after the flux has reached its minimum value and increased by an amount equal to the hysteresis.
MLX90217 Features and Benefits
- Rotary Position Gear Tooth Sensor
- Short Circuit Protection
- On-chip 10 bit A/D Converter
- Self-Adjusting Magnetic Range
- High Speed Operation
- No Chopper Delay
- Zero Speed Detection
- No Rotary Orientation Concerns
MLX90217 Environmental Information
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MLX90217 Frequently asked Questions
MLX90217 AS CRANK SENSOR..
Question
HI ALL!
CAN MLX90217 BE USED IN CRANK POSITION SENSING (ROTARY ORIENTATION INSENSITIVE)?
Answer
In principle, the MLX90217 could be used for an active crankshaft position sensor.
It will be able to deliver an electrical signal from the first-edge ("Zero-speed") up to 10000 RPM (i.e. 10 kHz input signal w/ Crank target 60-2 teeth) regardless of the direction.
You will not be able to meet the repeatibility specification required by the engine management control unit and strategy. This is linked to the working principle of the MLX90217 i.e. a fully digital track-and-hold circuitry.
For Crankshaft application, we recommend the MLX90254. This circuit is an AC-coupled differential Hall sensor. It can be used together w/ a back-bias magnet at the front of a ferromagnetic toothwheel. It can also be used at the front of a magnetic wheel.
The AC-coupled differential circuitry allows the MLX90254 to meet extremely tight jitter specification compatible w/ the engine management requirements.
However, it is not a zero-speed sensor.
MLX90217 HALL CHIP
Question
We are using MLX90217 in one of our speed sensing applications. The input frequency to the chip is 12khz. If the chip is exposed once to high speed sensing applications where input frequency will be 30khz will there be any performance degradation of the sensor once it is brought back to its normal speed sensing range.
Regards
Sujatha
MARKING DETAILS ON MLX90217
Answer
The only diferrence is the number of digital steps for the hysteresis.
Both MLX90217CA and CC fullfill the magnetic hysteresis specification of the product datasheet i.e. 1.8 mT ... 10 mT.
However, the typical hysteresis for the CA is around 4 mT while the CC is around 7 mT.
In other words, you can typically work at bigger airgaps using the Rev. CA. However your capability study for your application needs to be computed with the worst case hysteresis which is idential for both version i.e. 10 mT.
MELEXIS 90217 Operating Bias
Question
Could you please explain how the chip behavior is if bias magnet strength is 1.28tesla. Will the waveform obtained from it will be erratic at larger speed or it will not give any waveform at all.
The reason behind this question is:
We have used MLX90217LUA in one of our application for gear wheel speed sensing. The speed range is 3906 rpm & air gap between chip & wheel is 1.77mm max. The device marking on the chip is 17CA for first batch. We obtained the required waveform at maximum speed as well.
But now after manufacturing 50 products, the chip output is erratic at larger speed. We noticed the device marking on the chip as 17CC. CC on the device body indicates series & Die rev no. If you replace this chip with 17CA keeping all other items same, waveform appears normal. Other items include magnet & signal condioning PCB etc.
Could you please explain what could be the reason for difference in behavior of two different batch chips.
Question
We are finally arrived at the fact that magnet used by us has the surface gauss strength of 390mT. 12800G is actually the Br Value. Hence we could say that bias magnet used in our application is meeting the 50 to 400mT requirements as per 90217 data sheet.
Now please let me know how the chip behaves when it is affected by ESD. Will it cease functioning completely or still continue to work but there will be performance degration.
Please send us 5 new samples of MLX90217LUA Hall sensors to us in order to investigate cause of failure.
Question
We received the samples & tested for its functionality. But the problem is still persists. The output reading obtained is erratic after 3500RPM. Bias magnet used is having surface gauss strength of 390mT, which is well within the requirements as per the MLX90217 datasheet.
Kindly let us know what exact changes has been made in 17CC with respect to 17CA. This will enable us to resolve the issue as early as possible.
Question
Will it be possible for Melexis to supply MLX90217LUA Hall sensors with device marking 17CA in quantities of 100/200nos. per two month.
If so please let us know the availability of these MLX90217LUA Hall sensors in order to enable us to purchase it immediately.
MLX90217
Question
i am using MLX90217 hall effect sensor,i wanted to know,how much will be the maximum distance between sensor and magnets,and how can we convert the analog signal to digital output,if the rotation is high can the sensor able to get magnetic field.
I n the example it was mentioned that the magnet was attached to the back of sensor (non marked side )is it compulsory,i think the magnet has to attract the sensor ?
Answer
Hi, sorry for the late reply.
Prior answering your specific question, I would recommend you to look at the other Posts linked to the MLX90217 as there are precious information there.
From your message, I have the impression you plan to use the MLX90217 at the front of a rotating magnet. It can work that way of course even if the most common application is w/ a so-called back bias magnet (magnet at the back of the IC) and a ferrous rotating target at the front of the IC/magnet.
The IC senses the magnetic flux density and from the modulation of this flux density, it derives a digital output signal. The output transfer characteristic is based on track-and-hold circuit and the hysteresis for the peak detection is the value in the specification i.e. 1.8 mT up to 10.0 mT.
The modulation of the flux density can be generated by a spinning magnet (like you are doing apparently) or a spinning ferrous target at the front of the IC w/ a back bias magnet.
Answer
I have the impression that your are not using the right component for your application. MLX90217 is a gear-tooth sensor w/ track-and-hold circuitry. I do believe you need a simple Hall effect switch w/ fixed absolute threshold. Could you tell a bit more on your applications.
Question
Hello, i´m interested in the MLX90217,to use it in speed measurement, the problem is that i´m using a perforate disc with holes, the disc have 4mm of thickness, also the disc will move axially, reason why, the distance between the sensor and the disc, will variate around 10mm, so my question is the next: could be this a problem or not?.
Besides, i´m interested to know which is the minimun diameter of the disc perforations and the separation between this perforations?.
Thanks for the information you could supllies me, waiting for a soon answer
Answer
MLX90217 is a so-called mono-cell sensor i.e. it features only one Hall sensitive element. Consequently, it cannot provide the rotation direction information i.e. CW or CCW.
The sensors capable of doing that feature 2 sensitive elements for which the pitch should be used to build the target wheel (you want to have the pitch equal to one quarter of the full length "tooth-notch" in order to have 2 signals in quadrature and then an easy life w/ the determination of the rotation direction).
In summary, MLX90217 is more for "speed sensing" (RPM, pulse counting) applications.
However, by using a special ("shaped") target wheel as described on Page 5 of the datasheet and taking into account the working principle of MLX90217 i.e. peak detector, it is possible to get the information CW/CCW as a noticeable difference in duty cycle. This can work in practice but it needs of course to be characterized over the application airgap and airgap tolerance, temperature range, magnet tolerance...
You can possibly acheive your goals.
Question
We currently use the MLX90217 sensor for various speed sensing applications where we have a bias magnet at the back.
In one of our customers applications we have the problem that there are sometimes (1 in 1000 pulses or so) erratic pulses. We suppose it could be connected to the internal "intelligence" of the MLX90217 as it is a non standard target (something like a pin). Can you tell me where I can find additional information on the self adjustment mechanisms of the MLX90217? Or do you have another idea what could be the cause of the problem?
Question
Dear Sir or Madam
Pls give a hand in the using about MLX90217.We want to use the chip in the gear velocity measurement.The gear is one module and the teeth distance is 2mm,the distance is 4mm beteen the sensor and the teeth.Can you give some parameter about the magnet and gear.for instance the material of the magnet and the gear,their dimension etc.Special in the magnet paramet.
Look forward for your help.
Question
Pls give a hand in the using about MLX90217.We want to use the chip in the gear velocity measurement.The gear is one module and the teeth distance is 2mm,the distance is 4mm beteen the sensor and the teeth.Can you give some parameter about the magnet and gear.for instance the material of the magnet and the gear,their dimension etc.Special in the magnet paramet.
Answer
This item has already been discussed on the forum. Please have a look in some previous posted messages about the MLX90217.
To make your life easy, I have inserted it again below.
Any kind of magnet (SmCo, NdFeB, AlNiCo, Ferrite) can be used as long as the amplitude of the magnetic signal modulation (due to the rotation of the wheel i.e. succession of teeth and valleys => AC signal) at the IC level is more than 100 G (10 mT). This should be verified at maximum Airgap (i.e. max. distance between sensor and target wheel). Pay also attention to the magnetic bias itself (i.e. DC component of the magnetic flux density applied on the back side of the IC): it should be maintained below 4000 G (or 400 mT) w/ the proper polarity.
If you take a "cubic" magnet of 5 mm x 5 mm x 5 mm NdFeB and you place directly at the back of the IC, you should be fine.
For the gearwheel, if you take valleys w/ 4 mm depth, you should be fine.
Again, to do a good job, once in the design phase you should measure the field strength between magnet and target with linear hall sensor or gaussmeter and plot this to be sure the signal is adequate for reliable operation over temperature and life.
- rotary orientation
Question
In the MLX90217 product description it is mentioned there are no rotary orientation concerns. Can you specify this in more detail, i.e. what is the (small) influence of the rotary position with respect to a pole wheel. As far as I understood the Hall effect, there will be always be some kind rotary influence unless it is not compensated.
Magnet selection for Mlx90217 and Mlx90254
Question
My customer would like use MLX90217 for cam sensor and Mlx90254 for crankshaft sensor. And they don't very clear how to select magnet for these two chips. They ask for the documents about magnet selection for Mlx90217 and Mlx090254 and give the magnet and airgap vs. output signal curve. Would you please help me with this request?
Answer
Your question lacks some important details. The gear target geometry is equally important to the airgap vs. output signal curve.
A typical magnet for use with the MLX90217 or MLX90254 might be something like a NeFeB material, grade N35 or better and in a 5mm dia. x 8mm length. A rare earth SmCo material would also work and might give better temperature performance especially above 125C, although a good, quality supplier of NeFeB would have grades of Neo materal to meet high temp requirements. I also encourage your customer to read thoroughly the datasheets on the products to better understand how magnet selecion affects performnce
Buy MLX90217
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