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DA7280

LRA/ERM Haptic Driver with Multiple Input Triggers,

Integrated Waveform Memory and Wideband Support

Datasheet

Revision 3.0

30-Jul-2019

CFR0011-120-00

34 of 76

5.7

Advanced Operation

DA7280 features several advanced modes of operation to fine-tune actuator haptic performance.

5.7.1

Frequency Tracking

The closed-loop frequency tracking on DA7280 is implemented via a proportional-integral (PI)

controller. The proportional coefficient is stored in FRQ_PID_Kp_H/L and the integral coefficient in

FRQ_PID_Ki_H/L. The default values of the coefficients are optimized to cover a wide range of

actuators with typical settling times of approximately 40 ms from a 20 % frequency offset. If further

optimization is required to target a specific actuator the coefficients can be updated. The LRA tuning

tool in the DA7280 SmartCanvas GUI provides an intuitive and graphical way to easily adjust the Kp

and Ki coefficients.

To increase absolute accuracy of the lock during playback, DA7280 supports automatic scaling of the

frequency tracking controller proportional coefficient. This feature is enabled via

FREQ_TRACKING_AUTO_ADJ and becomes active after the device has achieved initial frequency

lock. The FRQ_LOCKED_LIM value is used to determine the threshold for the initial lock and can be

scaled up or down depending on system requirements. If optimizing FRQ_PID_K<x> coefficients with

the FREQ_TRACK_AUTO_ADJ enabled in normal operation, ensure that the closed loop is stable

for a step response when FREQ_TRACK_AUTO_ADJ is set at either 0 or 1.

The resonant frequency tracking algorithm converges to the correct value from up to 25 % offset

between the initial nominal datasheet value and the actual resonant frequency. This range is

conservative to prevent unwanted behavior. A fault triggers if the actuator resonant frequency is

outside the 50 Hz to 300 Hz range. To block these checks, set FREQ_TRACKING_FORCE_ON = 1.

FRQ_TRACK_BEMF_LIM disables the frequency tracking if the BEMF signal becomes too low. It

should always be set lower than the value in RAPID_STOP_LIM.

The instantaneous value of the resonant frequency period is updated every half-period and written to

LRA_PER_ACTUAL_H/L. The values can be converted to period using the following formula:

�� (��) = 1333.32 × 10−9 × (128 × ��_��_��_�� + ��_��_��_��)

(10)

If more accurate information is required (for example if a frequency tracking enabled sequence is

played to determine the resonant frequency before entering wideband operation), the average

resonant frequency information over the last four half-periods is written to

LRA_PER_AVERAGE_H/L. The values can be converted to period using the following formula:

�� (��) = 1333.32 × 10−9 × (128 × ��_��_��_�� + ��_��_��_��) (11)

5.7.2

Rapid Stop

The Rapid Stop algorithm relies on actuator BEMF sensing to detect actuator motion during a stop-

to-zero LRA acceleration. The algorithm provides a stopping signal to the LRA until the actuator

crosses the point of no acceleration. Since drive updates happen only at the zero cross point, this

introduces latency that may cause the actuator to overshoot the stop position. Due to this, the Rapid

Stop will also trigger at a pre-determined threshold set by RAPID_STOP_LIM. The default setup

covers most actuators, but if Rapid Stop is too short (actuator not fully stopped), the register value

should be decreased; and if Rapid Stop overshoots (actuator stopped and then reversed), the

Note: The Rapid Stop algorithm can be triggered only for sequences longer than three half-periods.

5.7.3

Initial Impedance Update

DA7280 performs an impedance measurement at the very first half-period of drive at the start of

playback. This allows a one-shot update of V2I_FACTOR_H/L to take into account specific actuator

DA7280 Datasheet(PDF) 34 Page - Dialog Semiconductor

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