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MLX90215
Precision Programmable Linear Hall IC
 Download MLX90215 Datasheet (PDF)
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MLX90215 General Description
The MLX90215 is a Programmable Linear Hall Effect sensor IC fabricated utilizing silicon-CMOS technology. It posesses active error correction circuitry which virtually eliminates the offset errors normally associated with analog Hall Effect devices. All magnetic response functions of the MLX90215 are fully programmable for even greater versatility.
The VOQ (VOUT@ B=0), sensitivity, direction of slope and the magnitude of sensitivity drift over temperature, are all programmable.
The ratiometric output voltage is proportional to the supply voltage. When using the supply voltage as a reference for an A/D converter, fluctuations of +10% in supply voltage will not affect accuracy. When programmed for a conventional sensitivity (with a positive gain), the voltage at the output will increase as a South magnetic field is applied to the branded face of the MLX90215. Conversely, the voltage output will decrease in the presence of a North magnetic field. The MLX90215 has a sensitivity drift of less than +1% error, and VOQ stability drift of less than +0.4% error, over a broad temperature range.
MLX90215 Features and Benefits
- Programmable Linear Hall IC
- Quad Switched / Chopper Stabilized
- Ratiometric Output for A/D Interface
- Adjustable Quiescent Voltage (VOQ )
- Very Low Quiescent Voltage Temperature Drift
- Adjustable Sensitivity
- Adjustable Temperature Compensation of Sensitivity
MLX90215 Environmental Information
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MLX90215 Frequently asked Questions
Linear Hall!
Question
Is it possibile to measure field up to 300mT with MLX90215EVA? And what about preprogrammed linear hall sensor MLX90215LVA-BC03(10mV/mT)?
Answer
Yes it is possible if you are only going to measure a single polarity field at 300mT. The offset (Voq) can be programmed to 1v or less and allow a signal span from 1v to 4v. This would result in the +300mt * 10mV/mT= 3V signal being within the span of the device. IF the field is of opposite magnetic polarity the arrangement could be swapped by setting the invert bit or by setting Voq to 4 volts or even by applying the field to the back of the VA package.
The standard device MLX90215LVA-BC03 would not work because the offset is programmed to 2.5v and only allows a signal span of approximately 2 to 2.4 volts in one magnetic polarity. So a field of +300mT would be clipped at the upper supply rail (practically speaking about 4.5 to 4.9 volts) . In this case it would only be possible to sense about 200 maybe 240mT when using the MLX90215LVA-BC03.
Hall chip weight on plate sensing
Answer
If there is application when you need only two states (on/off) then you can use hall latch like US1881,2881,...
Then you have two possibilityes. You can use permanent magnet and adjust distance betwen hall switch and magnet, or you can made a coil but you need very accurate current source. In this case your distance can be constant and you adjust sensitivity with current!
The first option is cheaper. Current source can be made with a few transistors for second option.
The third option is that you took pre-programmed linear sensor like MLX90215LVA-BC03 (10mV/mT). In this case you must build external hysteresis circuit(one op-amp)and you can adjust it with two resistors(loop)! Here you can also use permanent magnet!
Hall Sensor application
Answer
In substituting for a potentiometer the analaog products to consider include the MLX90215, 90251 or 90242. Other products to consider from our sister company, Sentron, would be the 2SA-10. All of these devices require some permanent magnet field source to drive the output through the desired range for the desired mechanical displacement. See our Hall effect applications guide for more details.
An encoder with digital outputs can be realized with a simple Hall effect digital switch or latch like the US188x,288x, 588x or even the MLX90224. All of these devices will require an appropriate multipole ring magnet to create the multiple pole transitions per revolution needed to implement an encoder function. There are also some ideas on this in the Hall applicaitons guide at www.melexis.com
Programming the MLX90215 manually
Question
I'm interested in programming the MLX90215 manually so that I can use it in RAM mode, although I realise that this 'is not intended for regular operation'!
Is there any more information about the programming waveforms, transfer rate and timings and so on? The datasheet and the FAQ are quite sketchy.
Answer
Is it for evaluation in the lab or to be used in a real application around a micro-controller (for example)?
In the first case, you should buy a MLX programming unit (e.g. PTC-04). It is delivered w/ all the necessary tools to program this part as well as other MLX programmable Hall sensors. It is a quite universal tool.
In the latter case, Melexis does not recommend this mode of operation as it was not the intention to let the device work permanently in RAM. This RAM mode is only for calibration purpose in conjunction w/ the programming unit i.e. in a well under-controlled environment. There is not enough check to guarantee this mode in a not-controlled environment (e.g. EMI perturbations,...). Furthermore, the programming protocol is based on "exotic" waveforms on the supply line (up to 15 V) and the output line. You will need to add dedicated H/W to make this happen.
In summary, we do not disclose the programming protocol for the MLX90215 and we recommend to use the ptc-04 in all cases.
Noise Filtering for MLX90215
Question
I'm looking for a Hall effect sensor with high sensitivity. MLX90215 seems to be matched most. However, for an application of measure the distance from magnet, I need to reduce the peak to peak noise.
I would like to work at 140mV/mT sensitivity. The noise will be 50mV. I'm thinking to set a low-pass filter at the output of sensor. However, I don't know which frequency I should choose. Could you please tell me the frequency of the noise at the output of this sensor?
Is there a better solution for this problem?
Answer
Low pass filter can only help and the lower the cut-off frequency, the better results you will get.
At the sensitivity range you are thinking i.e. 140mV/mT or 14 mV/G, the internal sampling frequency of the chip is already pretty low (4 kHz) and therefore a cut-off frequency of 500 Hz (or less) for your filter will be adequate to eliminate the noise components which are associated to the internal sampling.
You can also work w/ MLX90251 as this IC has also an on-chip filter you can set through the programming unit (e.g. together w/ offset and gain settings). Using the strongest filter (i.e. Filter = 15), you will already get a serious noise reduction and you may not need an external low-pass filter: a decoupling cap will be enough. Advantage of MLX90251 is that 140 mV/mT is not at the top end of its specification while MLX90215 gain settings is somewhat limited to this value.
In any case, all those filter (internal or external) considerations need to be checked vs. your bandwidth requirement for your application. If you do not have specific "speed" requirements, you have the complete freedom. If you have speed/response time/bandwidth requirements, then you need to consider those while dimensioning your filter.
PreProgrammed MLX90215
Question
Where is the datasheet for the pre-programmed MLX90215LVA-BC03.
US1881
Answer
As you have surmised correctly this is not an appropriate use for this IC. The current in a PCB trace is generally much too small and generates a very weak magnetic field. Usually the field is orders of magnitude smaller than the field required to switch an 1881 Hall Latch. Even our linear Hall ICs, like the MLX90215 or MLX90251 are not sensitive enough for this task. Melexis has a device called the CSA1V that can be used to detect certain currents flowing in a PCB trace. You can learn more about this part at http://www.sentron.ch/csa.htm. Sentron is a Melexis company that specialies in advanced magnetic sensor technologies.
To make the US1881 work would require a toroidal ferrite core with the 1881 inserted into an air gap in the core and then likely several hundred turns of copper magnet wire on the core. The current would then be run through this coil and the field in the gap would be a multiple of the amp turns of the windings. I am sure this is not what you had in mind so look at the CSA1V and see if it could meet your expectations. This IC uses very clever on chip flux concentrator technology to give a more sensitive detection solution without requiring ferrite cores and windings.
MLX90242LUA Hall Sensor
Answer
The 90242 does not have any user adjustable provision for temperature compensation of the magnetic material. The described temperature behavior indicates a Rare Earth Samarium Cobalt material is being applied. Is that correct? The Magnet is losing 3.5% of it field strength at the elevated temperature (128-25=103). This IC has a range for its' thermal coefficent of sensitivity and also for the drift of the null or Voq value. Both will influence the overall Vout drift due to the temperature change. But both have a statistical distribution within the typical range provided in the datasheet. It becomes quite limited to be able predict what any 1 IC will do without specifically characterizing that device over temperature and with a stable magnetic field (from an Helmholtz coil not a permanent magnet).
Meanwhile the MLX90215 or the MLX90251 are available as programmable Linear Hall IC's with the significant advantage that the temperature coefficient can be set to compensate for the loss in magnetic strength by increasing the gain of sensitivity an opposite amount.
General quesions for MLX90215
Question
Can I use the MLX90215 or MLX90251 ,with a cylindrical magnet, to measure rotary angle and have a linear output with regard to the angle?
Answer
Not easily, the MLX90215 and 90251 are Linear Hall effect Sensors. Meaning their output is linearly proportional to the strength of the sensed magnetic field. Unfortunately to obtain a linear relationship between rotation and magnet field strength is technically challenging. Magnetic fields are not linear and need fairly complex magnetic pole pieces and magnetic circuits to create linear fields even over relative small rotational displacements. And many of the best ideas are covered with patents.
The MLX90316 is specifically designed to simplify this challenge. It uses Triaxis(Registered Trademark) technology to make it possible to use a simple disk magnet and achieve 360 degree rotational sensors. Through simple programming it can also do small rotational angles as well.
Buy MLX90215
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