7.3.1 Support for ERM and LRA Actuators

Linear vibrators (also known as Linear Resonant Actuators or LRA in haptics terminology) vibrate only at their resonant frequency. Usually, linear vibrators have a high-Q frequency response, due to which there is a rapid drop in vibration performance at offsets of 3 to 5 Hz from the resonant frequency. Therefore, while driving a linear vibrator with the DRV8601, ensure that the commutation of the input PWM signal is within the prescribed frequency range for the chosen linear vibrator. Vary the duty cycle of the PWM signal symmetrically above and below 50% to vary the strength of the vibration. As in the case of DC motors, the PWM signal is typically generated using software, and many different advanced haptic sensations can be produced by applying different PWM signals into the DRV8601.

Figure 13. LRA Example for 1/2 Full-Scale Drive

The DRV8601 is designed to drive a DC motor (also known as Eccentric Rotating Mass or ERM in haptics terminology) in both clockwise and counter-clockwise directions, as well as to stop the motor quickly. This is made possible because the outputs are fully differential and capable of sourcing and sinking current. This feature helps eliminate long vibration tails which are undesirable in haptic feedback systems.

Figure 14. Reversal of Direction of Motor Spin Using DRV8601

Another common approach to driving DC motors is the concept of overdrive voltage. To overcome the inertia of the mass of the motor, they are often overdriven for a short amount of time before returning to the rated voltage of the motor in order to sustain the rotation of the motor. The DRV8601 can overdrive a motor up to the V_DD voltage. Overdrive is also used to stop (or brake) a motor quickly. The DRV8601 can brake up to a voltage of –V_DD. For safe and reliable overdrive voltage and duration, refer to the data sheet of the motor.

7.3.2 Internal Reference

The internal voltage divider at the REFOUT pin of this device sets a mid-supply voltage for internal references and sets the output common mode voltage to VDD/2. Adding a capacitor to this pin filters any noise into this pin and increases the PSRR. REFOUT also determines the rise time of VO+ and VO when the device is taken out of shutdown. The larger the capacitor, the slower the rise time. Although the output rise time depends on the bypass capacitor value.

7.3.3 Shutdown Mode

DRV8601 has a shutdown mode which is controlled using the EN pin. EN pin is 1.8-V compatible. By pulling EN pin low, the device enters low power state, consuming only 10 nA of shutdown current.