Texas Instruments DRV2605L, User Manual, Page: 23 / 37

ERM
Or
LRA
OUT+
OUT-
100k
100k
470 pF
470 pF
Ch1-Ch2
(Differential )
Oscilloscope
Ch1
Ch2
100k
470pF
100k
470pF
OUT
OUT- OUT+
From DRV2605L
www.ti.com
Measurement and Analysis
5 Measurement and Analysis
The DRV2605L uses PWM modulation to create the output signal for both ERM and LRA actuators. To
measure and observe the DRV2605L output waveform, connect an oscilloscope or other measurement
equipment to the filtered output test points, “OUT+” and “OUT–".
Figure 22. Terminal Block and Test Points
The DRV2605L 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
Figure 23 shows the DRV2605L unfiltered waveform and Figure 24 shows a filtered
version used for observation and measurement.
Figure 23. DRV2605L Unfiltered Waveform Figure 24. DRV2605L Filtered Waveform
If the DRV2605LEVM-CT filter is not used, TI recommends using a first-order, low-pass filter with a cutoff
between 1 and 3.5 kHz.
Figure 25 shows a recommended output filter for use while measuring and
characterizing the DRV2605L in the lab.
Figure 25. Measuring the DRV2605L Output Signal With an Analog Low-Pass Filter
23 SLOU389A – May 2014 – Revised June 2014 DRV2605L ERM and LRA Haptic Driver Evaluation Kit
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