Eccentric Rotating Mass Motor Control

Adding vibration to your product is a great way to create a sensory rich user experience. The easiest method to accomplish this is to add a small eccentric rotating mass (ERM) motor. These motors use imbalanced weight attached to the shaft to create uneven centripetal force about the axis of the shaft.

Using GreenPAK™ with low dropout regulators (LDOs), provides a fully customizable, low-power solution to drive and control a wide variety of small ERM motors appropriate for devices such as mobile phones, game controllers, etc. The programmable digital and analog resources in GreenPAK make it easy to implement custom features to differentiate your haptic experience as well as protection features to ensure smooth and safe operation, including:

Custom vibration strength
Custom vibration patterns and timing
Braking
Custom motor kick-start and
Over-current/short circuit protection
Over-temp protection

GreenPAK Benefits for ERM Motor Control

Flexibility
- GreenPAK VDD is 2.5 to 5.0 V
- GreenPAK has integrated delays for programmable button de-bounce
- GreenPAK’s Inter-Integrated Circuit (I2C) interface allows changes to vibration patterns and timing
- GreenPAK general-purpose input/output (GPIO) routing is flexible – Ensuring the least complexity in PCB routing
Power Consumption
- GreenPAK is low-power
System Stability
- GreenPAK has integrated LDO protection
- GreenPAK is Zero Code – Implementing features in hardware ensures stability
- GreenPAK can integrate many components ensuring fewer points of failure

Vibration Patterning and Strength

Using GreenPAK’s programmable digital and timing blocks it is possible to make a number of different vibration patterns. With the LDOs integrated into the GreenPAK, which can switch between two voltage outputs using digital logic and up to 32 different levels via I2C, it is also possible to create vibrations of different strengths.

Kickstart

To quickly start an ERM motor, it is useful to drive it at a higher voltage for a short duration. This overcomes the momentum of the still mass and allows for cleaner vibration patterns.

Braking

Some ERM motors include a special pin for braking. Using digital logic and GreenPAK’s configurable GPIO, driving the braking pin anytime the motor should stop is easy.

Pattern and Kickstart Circuit in GreenPAK

Protection

The LDOs in GreenPAK contain over-current and short circuit detection which will cause the LDO to shut down in the event of a failure. Additionally, using the integrated temperature sensor and programmable analog comparator (ACMP), it is easy to implement over-temperature shutdown as well.