Input

Output Drive

3.3 V

0 V

0%

50%

100%

-3.3 V

PWM Input Duty Cycle

DRV2603

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SLOS754A – JUNE 2012 – REVISED JANUARY 2014

ECCENTRIC ROTATING MASS MOTORS (ERM)

Eccentric Rotating Mass motors, or ERMs, are typically DC-controlled motors of the bar or coin type. ERMs can

be driven in the clockwise direction or counter-clockwise depending on the polarity of voltage across its two

terminals. Bi-directional drive is made possible in a single-supply system by differential outputs that are capable

of sourcing and sinking current. This feature helps eliminate long vibration tails which are undesirable in haptic

feedback systems..

Figure 13. Reversal of Motor Direction

Another common approach to driving DC motors is the concept of overdrive voltage. To overcome the inertia of

the motor's mass, they are often overdriven for a short amount of time before returning to the motor's rated

voltage to sustain the motor's rotation. Negative overdrive is also used to stop (or brake) an ERM quickly by

reversing the magnetic field of the driving coil(s).

ERM MODE

The DRV2603 is a compact, cost-effective driver solution for ERM motors. Most competing solutions require

external components for biasing or level-shifting, but the DRV2603 requires only one decoupling capacitor giving

a total approximate circuit size of 2 mm by 2 mm. This small solution size still comes packed with features such

as a level-shifted input, differential outputs for braking, constant drive strength over supply, edge rate control, and

a wide input PWM frequency range.

When in ERM mode, the DRV2603 employs a simple control scheme. A 100% input duty cycle gives full-strength

forward rotation, a 50% input duty cycle give no rotation strength, and a 0% duty cycle give full-strength reverse

rotation. Forcing the motor velocity towards reverse rotation is used to implement motor braking in ERMs. By

stringing together various duty cycles over varying amounts of time, a haptic motor control signal will be

constructed at the output to precisely drive the motor.

Figure 14. ERM Mode

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