Drv2604 Unfiltered Waveform; Drv2604 Filtered Waveform; Measuring The Drv2604 Output Signal With An Analog Low-Pass Filter - Texas Instruments DRV2604EVM-CT User Manual

Measurement and Analysis
The DRV2604 drives LRA and ERM actuators using a 20-kHz PWM modulated waveform, but only the
frequencies around the LRA resonant frequency or the ERM DC drive voltage are relevant to the haptic
actuator vibration. The higher frequency switching content does not contribute to the vibration strength of
the actuator and can make it difficult to interpret the modulated output waveform on an oscilloscope. The
oscilloscope image on the left shows the DRV2604 unfiltered waveform and the image on the right shows
a filtered version used for observation and measurement.
Figure 20. DRV2604 Unfiltered Waveform
If the DRV2604EVM-CT filter is not used, TI recommends using a 1st-order, low-pass filter with a cutoff
between 1kHz and 3.5kHz . Below is a recommended output filter for use while measuring and
characterizing the DRV2604 in the lab.
Figure 22. Measuring the DRV2604 Output Signal with an Analog Low-Pass Filter
18
DRV2604 ERM, LRA Haptic Driver Evaluation Kit
OUT+
ERM
Or
LRA
OUT-
Copyright © 2013, Texas Instruments Incorporated
Figure 21. DRV2604 Filtered Waveform
100k
470 pF
Ch1
(Differential )
Ch2
100k
Oscilloscope
470 pF
Ch1-Ch2
SLOU355 – March 2013
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