DRV2625 Datasheet, PDF (30/77 Pages) Texas Instruments – DRV2625 Ultra Low Power Closed-Loop LRA/ERM Haptic Driver with Built-In Library

DRV2625
SLOS879A – DECEMBER 2015 – REVISED DECEMBER 2015
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8.6.8 Waveform Playback Programming
8.6.8.1 Data Formats for Waveform Playback
The DRV2625 uses a signed data format (2's complement) to specify the magnitude and direction of the drive.
The actuator can be driven in either closed-loop or open-loop. In closed-loop, positive numbers indicate the
magnitude of the drive desired. Negative numbers are interpreted as a brake signal, which is automatic in closed-
loop. In open-loop, positive and negative numbers are required to specify amplitude magnitude for both driving
and braking. In the case that automatic braking is selected for open loop, then any negative number will be
interpreted as a brake signal.
8.6.8.2 Open-Loop Mode
In open-loop mode, the reference level for full-scale drive is set by the OD_CLAMP[7:0] parameter. A mid-scale
input value gives no drive signal, and a less-than mid-scale gives a negative drive value. For an ERM, a negative
drive value results in counter-rotation, or braking. For an LRA, a negative drive value results in a 180-degree
phase shift in commutation.
8.6.8.3 Closed-Loop Mode
In closed-loop mode, the DRV2625 device provides automatic overdrive and braking for both ERM and LRA
devices. Positive values indicate that acceleration is desired. Negative values and 0 indicate that braking is
desired.
The reference level for steady-state full-scale drive is set by the RATED_VOLTAGE[7:0] bit (when auto-
calibration is performed). The output voltage can momentarily exceed the rated voltage for automatic overdrive
and braking, but does not exceed the OD_CLAMP[7:0] voltage. Braking occurs automatically based on the input
signal when the back-EMF feedback determines that braking is necessary.
In the event that the user is concerned that the overdrive time may be too high for a particular actuator, the
OD_CLAMP_TIME[1:0] can be used to limit the amount of time spent in over-drive mode (a voltage above the
rated voltage). If the overdrive time is exceeded and the DRV2625 device is still attempting to overdrive the
actuator, a new clamp is enforced, which is specified in the RATED_VOLTAGE_CLAMP[7:0] parameter, which is
enforced until a brake signal is received. During braking, the device will be allowed to overdrive for the time
specified in the OD_CLAMP_TIME[1:0], and, if exceeded, the RATED_VOLTAGE_CLAMP[7:0] is enforced. This
feature ensures that the actuator will not be overdriven continuously for longer than desired.
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