Most Hall-effect switches have a fixed B_OP, which typically imposes design constraints on the placement and specifications of the magnet needed to ensure switching of the Hall-effect sensor at the desired distance. To allow design flexibility, many Hall-effect switches come with multiple device variants with different B_OP values; however, there are only a finite number of B_OP options available with a Hall-effect switch, which still puts constraints on the placement and specifications of the magnet.

The TMAG5328 Hall-effect switch, on the other hand, has an adjustable B_OP that can be programmed anywhere between 2 to 15 mT by applying a voltage or connecting a resistor to the ADJ pin of the device. By following simple formulas, it is easy to calculate what resistor value or voltage value is needed to set up the right B_OP value. The hysteresis value of the TMAG5328 is fixed to 1 mT, which results in the B_RP value being B_OP – 1 mT. As an example, if the B_OP is set to 5 mT, the B_RP would be set to 4 mT.

To set the B_OP of the TMAG5328 using an external resistor, connect the resistor between the ADJ and GND pins of the device. Figure 1-4 shows the relationship between B_OP and resistance defined as B_OP(mT) = R_ADJ(kΩ). The B_OP of the TMAG5328 must be set to a value between 2 mT and 15 mT, R_ADJ must be set between 2 kΩ and 15 kΩ.

The other method to setup the B_OP is to apply a voltage to the ADJ pin. The relationship between B_OP and voltage is defined as B_OP(mT)= V_ADJ(mV) × 0.0125. To apply a voltage on the ADJ pin, the voltage source must be able to settle within 4 µs after being exposed to a 80-µA current on the ADJ pin. Figure 1-5 shows that the TMAG5328 B_OP must be set to a value between 2 mT and 15 mT and the V_ADJ must be set between 160 mV and 1200 mV.