LRA/ERM Ultra-Low Power Haptic Driver with Multiple Input Triggers and Integrated Waveform Memory

R15DS0041EE0330 Rev.3.30

June 16, 2026

CFR0011-120-00

Page 33

6.7

Advanced Operation

DA7282 features several advanced modes of operation to fine-tune actuator haptic performance.

6.7.1

Frequency Tracking

The closed-loop frequency tracking on DA7282 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 DA7282 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, DA7282 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)

6.7.2

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 register value should be increased.

NOTE

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

6.7.3

Initial Impedance Update

DA7282 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 variation for increased

voltage accuracy of the drive. The result is reported to IMPEDANCE_H/L, which can be read by the host and

converted to impedance using the following formula:

������������������������������������������������ ������������������������������������������������������(������������������������������������������) = (������������������������������������������������������_������ × 4 + ������������������������������������������������������_������) × 0.0625Ω

(12)

To disable this feature, set V2I_FACTOR_FREEZE and CALIB_IMPEDANCE_DIS = 1.