Welcome to the training module on Chopper Stabilized, Precision Hall Effect Latches A3290 where you will study the concept of Latching hall-Effect Sensor and its features and applications
Latching Hall-effect sensors, often referred to as &quot;latches&quot;, are digital output. Here shows pictorial the two possible states of the latching sensor. The sensor is initially off and the output is shown to be high, which will be the full supply voltage. The output remains high until the positive field magnitude reaches BOP at which time the output switches on and the voltage drops to its low state (Vsat), typically <200 mV. If the magnetic field is reduced the sensor remains on and will remain on until the negative field magnitude reaches BRP.
Here shows basic operation of Hall Element which uses Whetstone's bridge and Chopper stabilization circuit which is used for Hall sensor where it cancels the mismatching of the resistor circuit by changing direction of current flow.
The A3290 and A3291 Hall effect latches are extremely temperature-stable and stress-resistant sensors, especially suited for operation over extended temperature ranges (up to 125°C). Superior high-temperature performance is made possible through Dynamic Offset Cancellation, which reduces the residual offset voltage normally caused by device package overmolding, temperature dependencies, and thermal stress. The two devices are identical except for their magnetic switch points.
The Hall effect sensor A3290 can goes into various application areas like to measure Speed, and it can be used in Rotary Encoder, revolution counting, Flow meter, Brushless motor commutation…Etc.
The outputs of the A3290/91 switch low (turn on) when a magnetic field perpendicular to the Hall sensor transitions through and exceeds the Operate Point threshold, BOP. This is illustrated in this slide. After turn-on, the output is capable of sinking 25 mA, and the output voltage reaches VOUT(SAT). These devices latch that is, after a south (+) polarity magnetic field of sufficient strength impinging on the branded face of the device turns on the device, the device remains on until the magnetic field is reduced below the Release Point threshold, BRP. At that transition, the device output goes high (turns off). The difference in magnetic operate and release points is the hysteresis, BHYS, of the device. This built-in hysteresis allows clean switching of the output, even in the presence of external mechanical vibration and electrical noise. When the devices are powered on, if the ambient magnetic field has an intensity that is between BOP and BRP , the initial output state is indeterminate. The first time that the level of B either rises through BOP , or falls through BRP , however, the correct output state is obtained.
This slide shows Thermal characteristics curve for the device A3290: The Package Thermal Resistance, RJA, is a figure of merit summarizing the ability of the application and the device to dissipate heat from the junction (die), through all paths to the ambient air. Power derating curve here shows for single layer PCB with LH Package and UA package, Double layered PCB with LH Package. The second curve is Power Dissipation versus Ambient temperature
Here is general Application information while using the A3290 device. And also few Thermal Characteristics of this device under Heat dissipate condition.
Here is information about Bandwidth of hall-effect sensor which is about 25kHz to 30kHz and Power-up Time.
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Study on Chopper Stabilized, Precision Hall Effect Latches
Study on Chopper Stabilized, Precision Hall Effect Latches <ul><li>Source: ALLEGRO MICROSYSTEMS </li></ul>
Introduction <ul><li>Purpose </li></ul><ul><ul><li>Study on Chopper Stabilized, Precision Hall Effect Latches </li></ul></ul><ul><li>Outline </li></ul><ul><ul><li>Basics of Latching Hall-Effect Sensor </li></ul></ul><ul><ul><li>Chopper Stabilized Technique </li></ul></ul><ul><ul><li>Features and Application of A3290 device </li></ul></ul><ul><ul><li>Functional Block Diagram </li></ul></ul><ul><ul><li>Application and Technical Information </li></ul></ul><ul><li>Content </li></ul><ul><ul><li>11 pages </li></ul></ul>
Latching Hall-Effect Sensors <ul><li>Latching Hall-effect sensors are digital output, Hall-effect switches which switch on with a positive magnetic field and switch off with a negative magnetic field. </li></ul><ul><li>Since these sensors latch on and latch off both magnetic polarities are required for operation. </li></ul><ul><li>The positive magnetic field >BOP will latch the sensor on. The sensor will remain on even as the positive field is reduced to zero. </li></ul><ul><li>The negative field reaches BRP. Once turned off at BRP the sensor remains off until the field is again reversed and Bop is reached. </li></ul>
Chopper-Stabilized Technique <ul><li>The Hall element can be considered as a resistor array similar to a Wheatstone bridge. </li></ul><ul><li>When using Hall effect technology a limiting factor for switch-point accuracy is the small signal voltage, VHALL, developed across the Hall element. </li></ul><ul><li>A large portion of the offset is a result of the mismatching of these resistors. </li></ul><ul><li>The A3290/1 use a proprietary dynamic offset cancellation technique, with an internal high-frequency clock, to reduce the residual offset. </li></ul><ul><li>The signal is then captured by a sample-and-hold circuit and further processed using low-offset bipolar circuitry. </li></ul><ul><li>The chopper-stabilizing technique cancels the mismatching of the resistor circuit by changing the direction of the current flowing through the Hall element. </li></ul>Hall element, basic circuit operation Chopper stabilization circuit
Features and Benefits of A3290 ▪ Symmetrical switch points ▪ Resistant to physical stress ▪ Superior temperature stability ▪ Output short-circuit protection ▪ Operation from unregulated supply ▪ Reverse battery protection ▪ Solid-state reliability ▪ Small package size
Applications <ul><li>Speed sensor </li></ul><ul><li>Rotary Encoder </li></ul><ul><li>Revolution counting </li></ul><ul><li>Flow meter </li></ul><ul><li>Brushless motor commutation </li></ul><ul><li>Anti-pinch sunroof / window lift motor commutation </li></ul>
Functional Block Diagram Hysteresis of ΔVOUT Switching Due to ΔB Block Diagram
Thermal Characteristics Power Derating Curve Power Dissipation versus Ambient Temperature
Application Information <ul><li>It is strongly recommended that an external bypass capacitor be connected between the supply and ground to reduce both external noise and noise generated by the chopper-stabilization technique. </li></ul><ul><li>The Package Thermal Resistance, RJA, is a figure of merit summarizing the ability of the application and the device to dissipate heat from the junction (die), through all paths to the ambient air. </li></ul><ul><li>Radiation from the die through the device case, RJC, is relatively small component of RJA. </li></ul>Typical basic application circuit
Technical Information Bandwidth The bandwidth of Hall-effect sensors is typically 25 kHz to 30 kHz. In this era of 2 GHz microprocessors 25 kHz appears to be rather slow. In reality it is very rare for bandwidth to be a concern. Few mechanical systems will require or are capable of moving or spinning magnets fast enough to approach 25 kHz. Power-Up Time Power-up time depends to some extent on the sensor design. Digital output sensors, such as the latching sensor, reach stability on initial power up in the following times. Sensor type Power-up time Non-chopped designs (such as A3187 family) <1 µs Chopper-stabilized (such as A3280 family) < 40 µs
Additional Resource <ul><li>For ordering the A3290, please click the part list or </li></ul><ul><li>Call our sales hotline </li></ul><ul><li>For additional inquires contact our technical service hotline </li></ul><ul><li>For more product information go to </li></ul><ul><ul><li>http://www.allegromicro.com/en/Products/Part_Numbers/3290/index.asp </li></ul></ul>Newark 1 Farnell 1 Newark 2 Farnell 2