Texas Instruments | Piezo Haptics With Integrated Waveforms: DRV2605L-Q1 and DRV2700 | Application notes | Texas Instruments Piezo Haptics With Integrated Waveforms: DRV2605L-Q1 and DRV2700 Application notes

Texas Instruments Piezo Haptics With Integrated Waveforms: DRV2605L-Q1 and DRV2700 Application notes
Application Report
SLOA255 – October 2017
Piezo Haptics With Integrated Waveforms:
DRV2605L-Q1 and DRV2700
ABSTRACT
The DRV2700 is a high-voltage piezo driver with an analog input. This device is one of the many haptic
feedback drivers that Texas Instruments™ offers. One design challenge many customers face using the
DRV2700 is the analog input. Generating an analog input signal can burden the processor and be
undesirable. This application note addresses this challenge and provides a solution.
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Contents
Introduction ...................................................................................................................
Bandwidth .....................................................................................................................
DRV2605L-Q1 Setup ........................................................................................................
DRV2700 Setup ..............................................................................................................
Test Results ..................................................................................................................
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3
4
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5
List of Figures
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Block Diagram................................................................................................................ 2
2
Amp Gain Bandwidth VBST 30 V
3
Am Gain Bandwidth VBST 55 V ........................................................................................... 3
4
Amp Gain Bandwidth VBST 80 V
5
Amp Gain Bandwidth VBST 105 V ........................................................................................ 3
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Final Test Setup
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10
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List of Tables
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DRV2605L-Q1 Settings ..................................................................................................... 4
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Programmable Gains ........................................................................................................ 4
Trademarks
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All other trademarks are the property of their respective owners.
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Piezo Haptics With Integrated Waveforms: DRV2605L-Q1 and DRV2700
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1
Introduction
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Introduction
The DRV2605 family of drivers (including the DRV2605L and DRV2605L-Q1) offer integrated waveforms
that ship with the device. These drivers use a Class-D output stage that switches around 20 kHz. With the
use of a simple low-pass filter, the DRV2605L-Q1 can be used as an input to the DRV2700. Figure 1
shows the block diagram for this solution.
VDD
L1
C(VDD)
VDD
C(BOOST)
SW BST
PUMP
R(FB1)
PVDD
FB
C(PUMP)
R(FB2)
DRV2700
VDD
3.3 V
Application
Processor
VDD
RPU
EN
VREG
RPU
Digital
Control
CVREG
REXT
GAIN0
GAIN1
GPIO
R(EXT)
EN
SDA
SDA
SCL
SCL
DRV2605L-Q1
C8
R4
PWM/GPIO
OUT+
IN-
OUT-
C9
R5
IN/TRIG
IN+
GND
C6
C7
Piezo
Element
GND
Optional
LPF
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Figure 1. Block Diagram
This configuration (see Figure 1) makes it possible to play waveforms through I2C from the DRV2605L-Q1
to the DRV2700. The DRV2700 amplifies the input signal to the desired voltage to drive the piezo
element. This voltage can be 200 Vpp differentially or 500 Vp with the use of a flyback. There are a few
configuration details that must be considered when using this setup.
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Piezo Haptics With Integrated Waveforms: DRV2605L-Q1 and DRV2700
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Bandwidth
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2
Bandwidth
The bandwidth for the DRV2700 is a function on the piezo load capacitance. Figure 2, Figure 3, Figure 4,
and Figure 5 show the relationship between the DRV2700 output voltage and frequency. For most cases,
the frequency will be well below the 20-kHz level. In this case, the low-pass filter between the DRV2605LQ1 and DRV2700 is optional. For best practice, TI recommends using a simple first order low-pass filter
along with DC blocking capacitors (C8 and C9 in Figure 1).
200
110
Output Voltage (VPP)
90
80
70
60
50
40
30
No Load
Load = 33 nF
Load = 100 nF
Load = 330 nF
Load = 1 µF
Load = 4.7 µF
175
150
Output Voltage (VPP)
No Load
Load = 33 nF
Load = 100 nF
Load = 330 nF
Load = 1 µF
Load = 4.7 µF
100
125
100
75
50
20
25
10
0
0
20
100
1k
Frequency (Hz)
10k
20k
20
Figure 2. Amp Gain Bandwidth VBST 30 V
1k
Frequency (Hz)
10k
20k
Figure 3. Am Gain Bandwidth VBST 55 V
350
300
200
150
100
50
No Load
Load = 33 nF
Load = 100 nF
Load = 330 nF
Load = 1 µF
300
Output Voltage (VPP)
No Load
Load = 33 nF
Load = 100 nF
Load = 330 nF
Load = 1 µF
250
Output Voltage (VPP)
100
250
200
150
100
50
0
0
20
100
1k
Frequency (Hz)
10k
Figure 4. Amp Gain Bandwidth VBST 80 V
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20k
20
100
1k
Frequency (Hz)
10k
20k
Figure 5. Amp Gain Bandwidth VBST 105 V
Piezo Haptics With Integrated Waveforms: DRV2605L-Q1 and DRV2700
Copyright © 2017, Texas Instruments Incorporated
3
DRV2605L-Q1 Setup
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DRV2605L-Q1 Setup
The DRV2605L-Q1 can be configured in closed or open-loop mode. The closed-loop mode is used to
track the BEMF voltage when driving LRAs and ERMs. For this use case, the DRV2605L-Q1 should be
configured in open-loop mode by changing the register 0x1D. Next, users should select the appropriate
frequency using register 0x20. The output voltage will be based on the OD_Clamp setting (register 0x17).
The DRV2700 gain settings are optimized for 1.8-VP input signal. Therefore, the OD_Clamp should be set
near 1.8 VP. Finally, the waveform must be selected using the waveform sequencer. Refer to DRV2605LQ1 Automotive Haptic Driver for LRA and ERM with Effect Library and Smart-Loop Architecture for a list of
the available waveforms. To trigger the waveform, there are a wide variety options including: external level
trigger, external pulse trigger, and internal trigger mode. External trigger modes uses the TRIG pin, and
the internal trigger activates through I2C. Table 1 lists a summary of these settings.
Table 1. DRV2605L-Q1 Settings
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DRV2605L-Q1 Setting
Register
Open-loop output voltage
0x1D
Value
0x5C
Open-loop frequency
0x20
240 Hz (0x2A)
OD_Clamp (VOUT)
0x17
0x55
Waveform sequencer 1
0x04
User choice
DRV2700 Setup
The DRV2700 should be set to the appropriate boost voltage and gain setting based on the piezo being
driven. Table 2 lists four gain settings that are tuned to four configurations for the boost voltage. The gain
settings are hardware selected through the two gain pins. The boost voltage should be set by configuring
the feedback resistors between VBST, FB, and GND.
Table 2. Programmable Gains
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GAIN1
GAIN0
Gain (dB)
0
0
28.8
0
1
34.8
1
0
38.4
1
1
40.7
Piezo Haptics With Integrated Waveforms: DRV2605L-Q1 and DRV2700
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Test Results
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5
Test Results
For the final test results, connect the DRV2605LEVM-CT and the DRV2700EVM as shown in Figure 6.
For this test, a few different waveforms from the DRV2605L library were selected. The piezo element
being tested is a piezo bender with the following dimensions: 38 mm × 3.8 mm × 3.2 mm. The piezo is
attached to a 100-g metal block, and the acceleration is tested using the DRV-ACC16-EVM (see DRVACC16-EVM Accelerometer User ’s Guide).
Figure 6. Final Test Setup
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Test Results
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To optimize performance, the BRT setting (0x10) must be set to –20 ms (0xFC). This signed register
removes braking. The output of the DRV2605LEVM is connected to the input jumper (J5) on the
DRV2700EVM. The input goes through a second order low-pass filter and DC blocking capacitors.
Figure 7, Figure 8, Figure 9, and Figure 10 show the differential output voltage and piezo acceleration
profile of the DRV2700 for four different waveforms in the DRV2605L library (same as the DRV2605L-Q1).
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Figure 7.
Figure 8.
Figure 9.
Figure 10.
Piezo Haptics With Integrated Waveforms: DRV2605L-Q1 and DRV2700
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Revision History
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Revision History
NOTE: Page numbers for previous revisions may differ from page numbers in the current version.
Date
Revision
Description
October 2017
*
Initial release
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Revision History
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