DA7281

LRA/ERM Haptic Driver with Multiple I²C

Addresses, Integrated Waveform Memory, and

Wideband Support

Datasheet

Revision 3.1

10-Feb-2022

CFR0011-120-00

39 of 87

© 2022 Renesas Electronics

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.

5.7.3

Initial Impedance Update

DA7281 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.

5.7.4

Amplitude PID

Some cylinder based ERMs generate excessively large-amplitude BEMF voltages. DA7281 can

compensate for this by reducing the drive current level, set AMP_PID_EN = 1. The result is an

improved haptic response. Figure 17 describes how the actuator voltage and current differs when

AMP_PID_EN enabled or disabled.

Time [s]

VOUT

IOUT

AMP_PID_EN = 0

Time [s]

BEMF Voltage

Time [s]

VOUT

IOUT

AMP_PID_EN = 1

Time [s]

IOUT drops automatically to compensate

BEMF and keep VOUT constant

Figure 17: Output Voltage and Current for Different AMP_PID_EN Values

Note: This is not usually required for LRAs as the amplitude of the BEMF is typically very low.

5.7.5

Wideband Operation

DA7281 natively supports wideband LRAs and allows continuous frequency updates to the output

signal while driving. Amplitude and frequency data use parallel data paths, for configuration see

Section 5.6.5. This section describes how to use the frequency component only.

For wideband operation, frequency tracking must be disabled, by setting FREQ_TRACK_EN = 0,

because drive at frequencies different from the actuator resonant frequency is required. Rapid Stop

and Active Acceleration also rely on frequency tracking so must be deactivated by setting