DRV2624 Datasheet, PDF (13/79 Pages) Texas Instruments – DRV2624 Ultra Low Power Closed-Loop LRA/ERM Haptic Driver with Internal Memory

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DRV2624
SLOS893A – DECEMBER 2015 – REVISED DECEMBER 2015
Feature Description (continued)
8.3.2.5.4 Loop-Gain Control
The DRV2624 device allows the user to control how fast the driver attempts to match the back-EMF (and thus
motor velocity) and the input signal level. Higher loop-gain (or faster settling) options result in less-stable
operation than lower loop gain (or slower settling). The LOOP_GAIN parameter controls the loop gain.
8.3.2.5.5 Back-EMF Gain Control
The BEMF_GAIN parameter sets the analog gain for the back-EMF amplifier. The auto-calibration routine
automatically populates the BEMF_GAIN bit with the most appropriate value for the actuator.
Modifying the SAMPLE_TIME parameter also adjusts the back-EMF gain. The higher the sample time the higher
the gain.
8.3.2.6 Actuator Diagnostics
The DRV2624 device is capable of determining whether the actuator is not present (open) or shorted. If a fault is
detected during the diagnostic process, the DIAG_RESULT bit is asserted.
The DRV2624 device also features actuator resistance measurement, which is available in the DIAG_Z_RESULT
parameter.
R_(act)= 478.43
DIAG _ Z _ RESULT[7 : 0]
˜
719 4 ˜ CURRENT _ K[7 : 0]
(3)
8.3.2.7 Automatic Re-Synchronization
For LRA actuators, the DRV2624 device features automatic re-synchronization, which automatically pushes the
actuator in the correct direction when a waveform begins playing while the actuator is moving. If the actuator is at
rest when the waveform begins, the DRV2624 device drives in the default direction.
8.3.3 Open-Loop Operation
In the event that open-loop operation is desired the DRV2624 device includes an open-loop drive mode that
overrides any close-loop parameter and is available through the digital interface.
When activated, the digital open-loop mode is available for pre-stored waveforms as well as for RTP mode.
The dynamic range for open-loop operation is set by the OD_CLAMP[7:0], which sets the maximum peak value.
Amplitude codes (either through RTP or internal memory) scales the output accordingly.
For LRA actuators, the OL_LRA_PERIOD parameter programs the operating frequency, which is derived from
the PWM output frequency, f_O(PWM).
8.3.3.1 Waveform Shape Selection for LRA
The DRV2624 offers a selection of either sine-wave or square-wave waveform shape in open-loop mode. The
WAVE_SHAPE_LRA parameter selects which shape to use. The WAVE_SHAPE_LRA parameter is ignored in
ERM mode and in closed-loop mode.
8.3.3.2 Automatic Braking in Open Loop
The DRV2624 offers automatic braking in open-loop for both ERM and LRA. To accomplish automatic braking,
the DRV2624 switches to close-loop during the braking period, therefore resorting to the close-loop waveform
shape. The AUTO_BRK_OL parameter can be use to enable or disable the automatic braking feature. To use
the automatic braking feature, the device must be configured appropriately for closed-loop operation.
8.3.4 Flexible Front-End Interface
The DRV2624 device offers multiple ways to launch and control haptic effects. The MODE parameter selects
from either using the waveform sequencer (and hence trigger the waveforms with either an internal or external
trigger), or by using RTP mode. Additional flexibility is provided by the multi-purpose TRIG/INTZ pin, which can
be configured with the TRIG_PIN_FUNC parameter.
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