SBAU393 December 2021 DRV5056
In this EVM, a contactless trigger is implemented using Hall-effect sensors, which reduces wear and tear compared to traditional triggers that use potentiometers and mechanical switches. This design includes 3D-printed trigger module with embedded magnet for illustrating a Hall-based trigger press mechanism. In this implementation, a magnet is placed so that it moves along with the trigger. As the trigger is pressed, the magnet approaches a DRV5056 linear Hall sensor, which translates the sensed magnetic flux density from the moving magnet into an output voltage. Since the sensed magnetic flux density and output voltage varies with the location between the magnet and the linear Hall sensor, the output voltage provides information on the location of the magnet, and therefore, the trigger displacement. This design translates up to 10 mm of trigger displacement into an output voltage.
A TPS22917 load switch is used to disconnect power to the linear Hall sensor and other components if the trigger is not pressed. To wake up the system to enter active mode, the design uses the DRV5032 Hall-effect switch for detecting when the trigger displacement exceeds the turn-on distance. When the sensed magnetic flux density of the wake-up Hall-effect switch exceeds the magnetic operating point (BOP) of the switch, the output of the Hall-effect switch is asserted low, which triggers the load switch to reconnect power to the linear Hall sensor.
In addition to the wake-up Hall-effect switch, additional DRV5032 Hall-effect switches are present for implementing optional protection against external magnetic fields. If these additional Hall-effect switches detect strong external magnetic fields, the design automatically disconnects power to the linear Hall sensor to disable the sensor's output, thereby preventing the EVM from accidentally turning ON due to strong external magnetic fields.
This protection also turns OFF a currently ON EVM when strong magnetic fields are present. Each of the tamper Hall sensors can be individually disabled, which enables the user to select the number of Hall sensors needed for their system based on their sleep current consumption and external magnetic field protection requirements.
This EVM supports standalone operation or connection to external systems for in-system evaluation. In standalone operation, the design is powered from AAA batteries that are inserted into the battery holder that comes with the HALL-TRIGGER-EVM. To illustrate status, the following LEDs are used:
LEDs on the output of each Hall-effect switch.
An LED added to the VCC input of the linear Hall sensor for indicating when the system is woken up from its sleep mode and the linear Hall sensor is powered.
An LED that changes its brightness based on how far the trigger is pressed.
For connecting to external systems for in-system evaluation, a TPS70933 LDO is included in the design to convert external battery voltages from 5 V to 30 V down to a 3.3-V rail that powers the design. Instead of connecting the DRV5056 power to the load switch output, the design can also be reconfigured so that the DRV5056 is powered from an external 3.3-V rail.