The adjustable B_OP of the TMAG5328 enables design flexibility that fixed B_OP Hall-effect switches cannot provide. The advantages of the TMAG5328 programmable B_OP include the following:

• Design Flexibility: The magnet-to-sensor distance at which the output of the sensor changes state depends on the B_OP, magnet material, and magnet dimensions. The B_OP can be adjusted on the TMAG5328, therefore the B_OP enables the following capabilities:
  • Reuse of TMAG5328 device across multiple platforms: Different hardware platforms often have different requirements for switching distance and magnet specifications. As an example, Figure 1-1 shows two refrigerator designs with different dimensions. If it desired for the switch to assert its output low when the door angle is at 2°, each refrigerator would require a Hall sensor with a different B_OP. According to Figure 1-3, the B_OP should be set to 7.87 mT so that the output of the switch typically is asserted low at 2°. The output of the Hall-effect switch would typically be asserted high at 2.2° . Figure 1-6 shows that refrigerator 2 requires a B_OP,TYP of 3.49 mT for the output of the switch to typically assert low at a door angle of 2°. The output would typically assert high at a door angle of 2.5° with this switch. The TMAG5328 can be reused in both of these refrigerator designs by only changing the voltage or resistor connected to its ADJ pin to produce the necessary B_OP for each design. Only using one Hall-effect switch provides better inventory management compared to using two different Hall-effect switches.
    Figure 1-6 Magnetic Flux Density vs Refrigerator Angle of Opening (Refrigerator 2).
  • Easy last minute design adjustments: If a magnet in a design changes, the magnetic flux density seen by the Hall-effect sensor would also change. The TMAG5328 can easily address the changes in observed magnetic flux density by adjusting its B_OP accordingly to reproduce a switching distance that is close to the switching distance before design adjustments. As an example, let’s say the magnet in refrigerator 1 of was changed from 10x10x10 to 7x7x7. Figure 1-7 shows that changing the magnet requires a B_OP of 3.17 mT for the output to be typically asserted low at 2°. In this case, the output would typically assert high when the door angle is at 2.4°. Alternatively, if the mechanical construction of a design changes in a way that requires a different magnet-to-sensor distance (similar to the two magnet-to-sensor distances in the refrigerators in Figure 1-3), the B_OP on the TMAG5328 can also be easily adjusted to meet the new resulting magnet to sensor switching distance requirements.
    Figure 1-7 Magnetic Flux Density vs Refrigerator Angle of Opening (Refrigerator 1 With Different Magnet).
• Reduced design time: To determine if a Hall sensor can be used in a design, prototyping or magnetic simulations are often performed. The adjustable B_OP on the TMAG5328 can accelerate both prototyping and magnetic simulations.
  • Easy and quick prototyping: In some systems, initial system prototyping is done by placing different Hall-effect switches with different B_OP specifications into a system to see how the B_OP options affect the desired magnet to sensor switching distances. Testing multiple B_OP options with fixed B_OP devices require hand soldering then testing multiple devices one by one, which is time consuming. However, because the B_OP of the TMAG5328 can be dynamically adjusted, it is not required to solder multiple devices to test B_OP. To test a specific B_OP with the TMAG5328, only the corresponding voltage must be applied to the ADJ pin of the device, which accelerates prototyping time. After determining the voltage that produces the desired B_OP, the final system can use a DAC to generate this voltage to recreate the desired B_OP. Alternatively, the voltage can be converted to a resistor value that produces the same B_OP so that the final system only requires a TMAG5328 and resistor.
  • Reduced simulation time: Magnetic simulations are used to determine the relationship between magnetic flux density sensed by the device and distance, similar to the relationship shown in Figure 1-3, Figure 1-6, and Figure 1-7. Depending on the utilized magnetic simulator, it could take a long time to run a simulation. Performing these types of magnetic simulations commonly require multiple simulation iterations, where the selected magnet, magnet-to-sensor distances, and B_OP can be iteratively adjusted until the desired switching behavior can be guaranteed. Having an adjustable B_OP, loosens design constraints, which reduces the time it takes to perform simulations to find a viable solution, thereby reducing time to market. As an example, let’s say that the conditions for Refrigerator 1 in Figure 1-3 are first simulated to determine the relationship in Figure 1-3. If only a 3.17 mT B_OP Hall sensor is available instead of the 7.87 mT B_OP needed to produce the 2° switching distance for the given magnet, the designer can try using a different magnet to see if using a different magnet helps meet their requirements. It could take a few simulation iterations to find that using a 7x7x7 magnet can produce the desired B_OP. However, if the TMAG5328 was used, the B_OP could be set to the 7.87 mT B_OP needed for the first simulation, thereby preventing the wasted time performing the additional simulation iterations.
• Enables new applications not typically available with fixed B_OP sensors: The adjustable B_OP of the TMAG5328 allows the device to be used for the following purposes:
  • Determining the sensed magnetic flux density seen by the switch: Omnipolar Hall-effect switches typically only provide information on whether the absolute value of the sensed magnetic flux density is greater than B_OP or less than B_RP. The TMAG5328, on the other hand, also enables a method to estimate the sensed magnetic flux density seen by the device, assuming that it is within the 2 to 15 mT range. The sensed magnetic flux density seen by the device can be determined by connecting a voltage source to the ADJ pin, setting the ADJ pin to 1.2 V, and then gradually decreasing the voltage until the output is asserted low. The voltage at which the output switches state can be converted to units of mT to estimate the magnetic flux density seen by the device. Section 2 provides more information on how to determine the sensed magnetic flux density seen by the switch.
  • Implementing a programmable Hall-effect switch with microcontroller-less standalone mode: A DAC with nonvolatile memory (NVM), such as the DAC43701 or TPL1401, can be paired with the TMAG5328 to create a programmable Hall-effect switch implementation. In this implementation, the DAC output is connected to the TMAG5328 output so that the DAC output voltage sets the B_OP of the TMAG5328. A microcontroller is only needed to initially configure the DAC nonvolatile memory to automatically generate the voltage needed to implement the desired B_OP. After the DAC is configured, the microcontroller is no longer needed in the system. The DAC will automatically drive the TMAG5328 to create the desired B_OP, even after subsequent system power ON or reset events. Instead of relying on applying a specific condition on the device’s VCC pins, this programmable Hall-effect switch implementation uses the DAC communication interface (SPI, I2C, and so forth) to program the switch, which makes it easier to program or dynamically change the B_OP. The DAC communication interface often can support multiple devices on the same interface, therefore multiple DAC+switch systems can be connected to the same bus for faster programming. Section 3 provides more information on how to use the DAC with NVM for implementing a programmable Hall-effect switch.
  • Implementing diagnostics: A square wave can be applied to the TMAG5328 to implement diagnostics for detecting faults such as TMAG5328 device pin shorts, TMAG5328 device pin disconnections, and when a system’s magnet is either too close or too far from the sensor. The magnet out-of-range functionality implemented for diagnostics can also be reused as a magnetic window comparator instead. Section 4 provides more details on this.