Texas Instruments DRV2700EVM-HV500 User manual

User's Guide
SLOU407A–April 2015–Revised May 2015
DRV2700EVM-HV500 High Voltage Piezo Driver Evaluation
Kit
The DRV2700 is a single chip high-voltage driver with an integrated 105-V boost switch, integrated power
diode, and integrated fully differential amplifier. This evaluation kit utilizes this high-voltage switch into a
flyback configuration that is able to achieve (but is not limited to) up to 500 V:
• Controllable input modes: Analog input, PWM and MSP430 controllable
• Variable output voltages from 0 V to 500 V
• 2 power supply inputs to isolate power consumption on DRV2700 application circuitry
• 4 convenient max output voltage settings
• Small footprint (14 mm x 14.5 mm)
The evaluation kit is designed for all-around use and can be used not only for evaluation but can also be
used for prototyping into systems for driving piezo actuators, polymers, valves and many other
applications. The EVM also contains a microcontroller, LDO (3.3 V) and LEDs for status and input
settings.
Evaluation Kit Contents:
• DRV2700EVM-HV500 evaluation board
• Demonstration mode firmware preloaded onto microcontroller
• Downloadable software to control EVM
• Mini-B USB cable
Needed for programming and advanced configuration:
• Code Composer Studio™ (CCS) for MSP430
• MSP430 LaunchPad™ (MSP-EXP430G2) or MSP430-FET430UIF hardware programming tool
• DRV2700EVM firmware available on the DRV2700EVM-HV500 tool folder
Code Composer Studio, LaunchPad are trademarks of Texas Instruments.
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Contents
1 Getting Started............................................................................................................... 6
1.1 Evaluation Module Operating Parameters....................................................................... 6
1.2 Quick Start Board Setup........................................................................................... 7
1.3 Connecting a Load.................................................................................................. 7
2 Overview of EVM ............................................................................................................ 8
2.1 DRV2700............................................................................................................. 8
2.2 Microcontroller (MSP430).......................................................................................... 8
2.3 Power Supply Inputs and Path.................................................................................... 8
2.4 EN Configuration.................................................................................................... 9
2.5 Inputs................................................................................................................. 9
2.6 Outputs............................................................................................................... 9
2.7 TRIG Button ......................................................................................................... 9
3 EVM Control Software (GUI).............................................................................................. 10
4 Flyback Converter.......................................................................................................... 12
4.1 Programming the HV Maximum Output Voltage .............................................................. 13
4.2 Programming the Flyback Current Limit........................................................................ 14
4.3 Transformer Selection ............................................................................................ 14
4.4 HV Capacitor Selection........................................................................................... 14
5 PWM and Analog Inputs .................................................................................................. 15
5.1 PWM Input Using MSP430....................................................................................... 15
5.2 Analog Input ....................................................................................................... 16
6 Output........................................................................................................................ 17
6.1 Load Selection..................................................................................................... 17
6.2 Pulldown Network ................................................................................................. 17
7 Input Filter................................................................................................................... 19
7.1 First Order Filter................................................................................................... 19
7.2 Integrator ........................................................................................................... 19
8 Reference ................................................................................................................... 20
8.1 Schematic .......................................................................................................... 20
8.2 PCB Layout ........................................................................................................ 21
8.3 Bill of Materials .................................................................................................... 22
List of Figures
1 Board Diagram............................................................................................................... 6
2 Power Path Diagram ........................................................................................................ 8
3 Output Diagram .............................................................................................................. 9
4 GUI Interface................................................................................................................ 10
5 Low PWM Frequency...................................................................................................... 11
6 Mid PWM Frequency ...................................................................................................... 11
7 High PWM Frequency ..................................................................................................... 11
8 Arbitrary Waveform Using Wavebuilder Tab............................................................................ 11
9 VHV Feedback Network..................................................................................................... 13
10 PWM Signal................................................................................................................. 15
11 10-Hz Input Signal ......................................................................................................... 16
12 100-Hz Input Signal........................................................................................................ 16
13 Instantaneous Max Load Current vs Max Output Voltage............................................................ 17
14 Pulldown Network .......................................................................................................... 18
15 With FET Pulldown......................................................................................................... 18
16 Without FET Pulldown..................................................................................................... 18
17 Input Filter................................................................................................................... 19
18 DRV2700EVM-HV500 Schematic........................................................................................ 20
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19 Top and Bottom Layers.................................................................................................... 21
WARNING
EXPORT NOTICE
Recipient agrees to not knowingly export or re-export, directly or
indirectly, any product or technical data (as defined by the U.S.,
EU, and other Export Administration Regulations) including
software, or any controlled product restricted by other applicable
national regulations, received from Disclosing party under this
Agreement, or any direct product of such technology, to any
destination to which such export or re-export is restricted or
prohibited by U.S. or other applicable laws, without obtaining prior
authorization from U.S. Department of Commerce and other
competent Government authorities to the extent required by those
laws. This provision shall survive termination or expiration of this
Agreement. According to our best knowledge of the state and end-
use of this product or technology, and in compliance with the
export control regulations of dual-use goods in force in the origin
and exporting countries, this technology is classified as follows:
US ECCN: 3E991
EU ECCN: EAR99
And may require export or re-export license for shipping it in
compliance with the applicable regulations of certain countries.
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Cautions and Warnings
CAUTION:
Warning! Do not leave EVM powered when unattended.
HOT SURFACE:
Warning Hot Surface! Contact may cause burns. Do not touch. Please take the proper
precautions when operating.
HIGH VOLTAGE:
Danger High Voltage! Electric shock possible when connecting board to live wire. Board should
be handled with care by a professional. For safety, use of isolated test equipment with
overvoltage/overcurrent protection is highly recommended.
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WARNING
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General Texas Instruments High Voltage Evaluation (TI HV EVM) User Safety Guidelines
Always follow TI’s setup and application instructions, including use of all interface components within their
recommended electrical rated voltage and power limits. Always use electrical safety precautions to help
ensure your personal safety and those working around you. Contact TI's Product Information Center
http://support/ti./com for further information.
Save all warnings and instructions for future reference.
Failure to follow warnings and instructions may result in personal injury, property damage, or
death due to electrical shock and burn hazards.
The term TI HV EVM refers to an electronic device typically provided as an open framed, unenclosed
printed circuit board assembly. It is intended strictly for use in development laboratory environments,
solely for qualified professional users having training, expertise and knowledge of electrical safety
risks in development and application of high voltage electrical circuits. Any other use and/or
application are strictly prohibited by Texas Instruments. If you are not suitable qualified, you should
immediately stop from further use of the HV EVM.
1. Work Area Safety
(a) Keep work area clean and orderly.
(b) Qualified observer(s) must be present anytime circuits are energized.
(c) Effective barriers and signage must be present in the area where the TI HV EVM and its interface
electronics are energized, indicating operation of accessible high voltages may be present, for the
purpose of protecting inadvertent access.
(d) All interface circuits, power supplies, evaluation modules, instruments, meters, scopes and other
related apparatus used in a development environment exceeding 50Vrms/75VDC must be
electrically located within a protected Emergency Power Off EPO protected power strip.
(e) Use stable and nonconductive work surface.
(f) Use adequately insulated clamps and wires to attach measurement probes and instruments. No
freehand testing whenever possible.
2. Electrical Safety
As a precautionary measure, it is always a good engineering practice to assume that the entire EVM
may have fully accessible and active high voltages.
(a) De-energize the TI HV EVM and all its inputs, outputs and electrical loads before performing any
electrical or other diagnostic measurements. Revalidate that TI HV EVM power has been safely de-
energized.
(b) With the EVM confirmed de-energized, proceed with required electrical circuit configurations,
wiring, measurement equipment connection, and other application needs, while still assuming the
EVM circuit and measuring instruments are electrically live.
(c) After EVM readiness is complete, energize the EVM as intended.
WARNING: WHILE THE EVM IS ENERGIZED, NEVER TOUCH THE EVM OR ITS ELECTRICAL
CIRCUITS AS THEY COULD BE AT HIGH VOLTAGES CAPABLE OF CAUSING ELECTRICAL
SHOCK HAZARD.
3. Personal Safety
(a) Wear personal protective equipment (for example, latex gloves or safety glasses with side shields)
or protect EVM in an adequate lucent plastic box with interlocks to protect from accidental touch.
Limitation for safe use:
EVMs are not to be used as all or part of a production unit.
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USB Input
EXT Input
Power
Routings
Max Output
Voltage Switches
Output
Terminal
EN Header
SBW
Connector
PWM
Disconnect
Input Signal
DRV2700 HV
Circuit
Footprint
MSP430
(Microcontroller)
Getting Started www.ti.com
1 Getting Started
The DRV2700EVM-HV500 is designed for flexible use for prototyping as well as evaluation. Figure 1
shows the names and locations of the various elements on the EVM. To power the board, connect the
DRV2700EVM-HV500 to an available USB port on your computer using a mini-B USB cable. The default
board settings cause the microcontroller (MSP430) to control the inputs of the DRV2700 at power up. The
MSP430 has each of these control settings low which disables the DRV2700, by default. Figure 1 shows
the basic board diagram of the DRV2700EVM-HV500. Table 2 shows the original configuration of the
jumpers, as shipped.
Figure 1. Board Diagram
1.1 Evaluation Module Operating Parameters
Table 1 lists the operating conditions for the DRV2700 on the evaluation module.
Table 1. Typical Operating Conditions
Parameter Specification
Supply voltage range 3.6 V to 5.5 V
Power-supply current rating 500 mA
Input voltage 0 V to VDD
Max output voltage 500 VP*
*Maximum output voltage will vary based on feedback resistors and opamp variability.
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1.2 Quick Start Board Setup
The DRV2700EVM-HV500 comes with preprogrammed firmware to provide a 0- to 500-Vp signal between
the output and GND.
1. Out of the box, the jumpers are set to begin demo mode using USB power. The default jumper settings
are found in Table 2.
2. Connect a mini-USB cable to the USB connector on the DRV2700EVM-HV500 board.
3. Connect the other end of the USB cable to an available USB port on a computer, USB charger, or USB
battery pack.
4. If the board is powered correctly, the 5-V LED is on.
5. Enable the output using the GUI or programmatically through the computer, see GUI Interface for
additional assistance. If using an external input signal, EN the output by changing the jumper (JP3) or
equivalent control signal.
6. Once the output is EN, the device allows for the high-voltage output.
Table 2. Default Jumper Settings
Jumper
Parameter Default Specification
Setting
Open Disconnected PWM input and I/O of MSP430
JP1 PWM Connected X Connected PWM input and I/O of MSP430
Open DRV2700 not connected to either power supply
JP4 DRV VIN(1) DRV2700 connected to VIN power supply
USB(1) X DRV2700 connected to USB power supply
Open EN pulled internally to GND through DRV2700 internal resistance
JP3 EN PU(1) EN pulled up to MSP power supply through external pull up resistor
MSP(1) X EN tied to I/O of MSP430
Open DRV2700 not connected to either power supply
JP4 DRV VIN(1) DRV2700 connected to VIN power supply
USB(1) X DRV2700 connected to USB power supply
(1) In the table, jumper setting name means that side of the terminal is connected to the middle of the 3-terminal header. For
questions, refer to Figure 1.
1.3 Connecting a Load
1. With the power supply off, connect the negative terminal of the load to GND and connect the positive
terminal of the load to the "HIGH VOLTAGE" side of JP2.
2. Ensure the terminals are connected correctly, then enable the supply
CAUTION
Before connecting the load, ensure that the load is rated for the selected output
voltage. If not, see the Programming the HV Maximum Output Voltage section
to adjust the DRV2700 maximum output voltage.
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USB
Power
VIN
External
MSP HeaderDRV Header
Power to Rest of Board
Power to DRV2700
Overview of EVM www.ti.com
2 Overview of EVM
The following sections provide a description of each of the blocks identified in Figure 1.
2.1 DRV2700
The DRV2700 is a single-chip, high-voltage piezo driver with an integrated 105-V boost switch, integrated
power diode, and integrated fully-differential amplifier. This EVM allows the designer to evaluate this
device and appropriately prototype it into their design. See the DRV2700 (SLOS861) datasheet for more
in-depth information.
2.2 Microcontroller (MSP430)
An onboard MSP430F5510 is used to control the various input signals as well as communicate through
the USB to the GUI. See the Quick Start Board Setup section for how to setup and run with the GUI.
2.3 Power Supply Inputs and Path
Two power supply inputs are available to power the EVM: USB power and VEXTERNAL (Ext VIN on the EVM).
Each of these inputs can be used to power the entire board or parts of the board.
2.3.1 USB Power Input
The USB power input can be supplied from a standard USB port on a computer, USB charger, or USB
battery pack. This input is intended for ease-of-use and can be routed to power all circuitry on the EVM.
Additionally, this input has a 5-V LED indicator showing that power is being supplied to the EVM. If the
GUI is going to be used, the USB must be connected to the computer and JP2 routed to USB connection.
2.3.2 VIN/External Power Input
Provide the VIN power input with an external 3.6- to 5.5-V power supply. Additionally, this input can power
the entire board.
2.3.3 Power Path Selection
Each of the two power supply inputs can be routed to the DRV2700 or the rest of the IC. The positions of
the jumpers are described in Table 2 or can be read from the silkscreen of the EVM. Figure 2 shows the
basic diagram of the power paths.
Figure 2. Power Path Diagram
If a power measurement of the DRV2700 circuitry is desired, it is best to provide the MSP jumper (JP2)
with USB power and the DRV jumper (JP4) with VIN. With this configuration, measuring the provided
voltage and current into VIN gives the power consumption of the DRV2700.
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GND
High Voltage
Output
www.ti.com Overview of EVM
2.4 EN Configuration
The EN input for the DRV2700 has 4 different driving configurations:
• Driven through the MSP430. This is done by connecting the configuration jumper to the “MSP” state
(default).
• Pulled to a logic level high through pullup resistor. This is done by connecting the configuration jumper
to the “PU” state.
• Pulled to a logic level low through internal pulldown resistor. This is done by removing the configuration
jumper.
• Driven externally. This is done by connecting the external control signal to the center 100-mil header.
This signal has an LED to indicate when the signal is at a logic-level high.
2.5 Inputs
The analog input (TP1) is used for PWM and analog inputs. See PWM and Analog Inputs, for more
information.
2.6 Outputs
The DRV2700EVM-HV500 has a high voltage output ranging from 0–500 V. This output is routed to a
terminal connector to mitigate the user touching between the high voltage node and GND. Be sure to
disable power when connecting and disconnecting the high voltage node.
Figure 3. Output Diagram
2.7 TRIG Button
The DRV2700EVM-HV500 has a built-in trigger button for user prototyping. If different modes of operation
are desired without using the GUI, the MSP430 can be programmed such that the trigger button can cycle
through different modes.
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PWM Frequency
Control
PWM Duty Cycle
Control
EN/Disable
EN/Disable
Indicator
0-99 Single Point
Adder to Waveform
Quick Sample
Waveforms
Start/Stop Button
Expected Waveform
User Generated
waveform from
Excel/Text
Quick Launch
Freq Buttons
Repeat Waveform
EVM Control Software (GUI) www.ti.com
3 EVM Control Software (GUI)
By default, the DRV2700EVM-HV500 can be controlled programmatically through the GUI Interface.
Figure 4 is a screenshot of the GUI.
Run the GUI by downloading it from the DRV2700EVM-HV500 tool folder, installing the GUI and then
running it. When prompted, connect to the USBHID setting.
Figure 4. GUI Interface
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www.ti.com EVM Control Software (GUI)
The GUI is broken up into two tabs: Standard Drive and WaveBuilder. The Standard Drive utilizes
changing the frequency and duty cycle of the PWM signal and is intended for easy prototyping and
evaluating. The WaveBuilder tab is for showcasing the DRV2700 as a proportional controller that can
drive a variety of user-created waveforms. On both tabs, the sections are intuitive, however, the following
sections are worth describing:
•Output Timing: This button has 3 different modes: Continuous,Pulsed, and Single. These modes help
with a timed EN signal.
•Boost Voltage Percentage: This is the duty cycle of the PWM waveform and after filtered will be a
DC value to modulate the output. Note in the scopeshots in Figure 5 through Figure 8, that the PWM
signal's duty cycle is inverse to the output. (As duty cycle increases, the output voltage percentage
decreases.) This has been taken care of through software so that the slider bar will reelect the true
output percentage though. The boost voltage percentage will only have a true "Boost Voltage
Percentage" effect during High Frequency/DC Mode.
•PWM Input Frequency: This will change the frequency of the PWM signal coming from the
microcontroller, which is fed into the input filter:
– Low PWM Frequency (< 1 kHz): When below 1 kHz, the PWM signal will hardly be attenuated such
that the majority of the PWM signal will propagate through. This will cause the output to try and
reflect the PWM signal coming from the microcontroller and the output will try to be a square wave.
The AC Mode -Quick Launch frequency button will set the frequency to this range.
– Mid PWM Frequency (1 kHz < freq < 20 kHz): When the frequency is set in this range, the PWM
signal will be somewhat attenuated and the output will still somewhat reflect a PWM signal. This
mode can be used for audio tones, however, the output may not be able to drive to full scale,
depending on the load capacitance.
– High PWM Frequency (> 20 kHz): As the frequency starts to go higher, the PWM signal will be
greatly attenuated. This will cause the PWM signal to appear DC after this filter. This mode can be
used to drive the output at a DC level which is set by the Boost Voltage Percentage (that is, duty
cycle). The DC Mode -Quick Launch frequency button will set the frequency to 50 kHz, which is in
this range.
•Time Between Steps (ms): The time between steps on the wavebuilder tab is the time step between
points. This is implemented using a series of DC set points occurring at a certain time of the waveform.
The output is limited to 200 sample points.
•Waveform From Excel/Text: This text box will build a waveform in the graph based on a comma-
separated string of integers from 0-100%.
It is best practice to have an oscilloscope measure the output to verify how the load is actually being
driven, based on the conditions applied.
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Flyback Converter www.ti.com
VDD = 5 V C(LOAD) = 22 nF VHV = 0 to 500 V VDD = 5 V C(LOAD) = 22 nF VHV = 0 to 500 V
Figure 5. Low PWM Frequency Figure 6. Mid PWM Frequency
VDD = 5 V C(LOAD) = 22 nF VHV = 0 to 500 V VDD = 5 V C(LOAD) = 22 nF VHV = 0 to 500 V
Figure 7. High PWM Frequency Figure 8. Arbitrary Waveform Using Wavebuilder Tab
4 Flyback Converter
The DRV2700 device creates a boosted supply rail with an integrated DC-DC converter that can go up to
105 V. The switch-mode power supplies have a few different sources of losses. When boosting to very
high voltages, the efficiency begins to degrade because of these losses. The DRV2700 device has a
hysteretic boost design to minimize switching losses and therefore increase efficiency. A hysteretic
controller is a self-oscillation circuit that regulates the output voltage by keeping the output voltage within a
hysteresis window set by a reference voltage regulator and, in this case, the current-limit comparator.
Hysteretic converters typically have a larger ripple as a trade-off because of the minimized switching. This
ripple is a function of the output capacitor, internal delays, and the hysteresis of the control loop.
Before connecting the load, ensure the load is rated for the current boost voltage setting.
See Programming the HV Maximum Output Voltage for more information on how to set the boost voltage.
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www.ti.com Flyback Converter
4.1 Programming the HV Maximum Output Voltage
The high voltage output (HV) is set through an external network. For ease-of-use of this EVM, two
switches (SW3 and SW4) are installed to change RFB1 and CFB2 with ease. For a normal application,
switches should not be needed and those values can be set by passives.
Additionally, RFB2 is split into two resistors to provide a reference voltage for the pull-down operational
amplifier (opamp) that is discussed in Pulldown Network.
Figure 9. VHV Feedback Network
The HV output voltage is given by: Equation 2
(1)
where VFB = 1.30 V and VOP is the VOL of the opamp since it cannot go all the way to ground. TI
recommends the sum of the resistance of RFB1 and RFB2 be between 500 kΩand 1 MΩ.
The capacitors are needed in the feedback network to increase the performance at low and high
frequencies. Because the charge storage is inversely proportional to the capacitance, use Equation 2 to
calculate the values of the capacitors. In general, select a value around 22 pF for CFB1 and size CFB2
accordingly.
(2)
Refer to Table 3 for the switch setting to change the maximum output voltage.
CAUTION
Be sure not to hot switch the SW3 and SW4 connection. This should only be
switched while the output is disabled or the board is unpowered.
Table 3. VHV Setting Based on the Jumper Configuration
SW3 SW4 RFB2 CFB2 RFB1 CFB1 VMAX
Down Down 5.49 kΩ8200 pF 2.05 MΩ22 pF 500 V
Down Up 5.49 kΩ4505 pF 1.122 MΩ22 pF 275 V
Up Down 5.49 kΩ3717 pF 0.866 MΩ22 pF 212 V
Up Down 5.49 kΩ2710 pF 0.642 MΩ22 pF 158 V
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REF
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Flyback Converter www.ti.com
4.2 Programming the Flyback Current Limit
The peak inductor current is set with resistor R3 (REXT). The current limit is not a safety mechanism, but
the highest value current the inductor will see each cycle. The inductor must be capable of handling this
programmed limit during normal operation. The relationship of REXT to ILIM is approximated with Equation 3
where ILIM is the current limit set by REXT, K = 10500, VREF = 1.35 V and RINT = 60 Ω.
(3)
4.3 Transformer Selection
Transformer selection plays a critical role in the performance of the DRV2700. The range of
recommended primary-side inductance values is 3.3 µH to 22 µH. When a larger inductance is chosen,
the DRV2700 flyback converter automatically runs at a lower switching frequency and incurs less
switching losses; however, the larger inductances may also have a higher equivalent series resistance
(ESR), which will increase the parasitic inductor losses.
Another factor to consider for transformers is the winding ratio. In general, if a 200-V output is desired
then, because the SW node can boost up to 100 V, a transformer of 1:2 (100 V:200 V) is the minimum
required winding. However, selecting a slightly higher winding ratio to ensure that the 100 V on the
primary side is not surpassed while trying to boost up to the desired voltage is good design practice.
The transformer used on this EVM is a 1:10 winding ratio with a primary side inductance of 7 µH.
4.4 HV Capacitor Selection
The HV output voltage may be programmed as high as 500 V on this EVM. A capacitor must have a
voltage rating equivalent to the boost output voltage or higher. Because the output can be unloaded, a 1-
nF output capacitor is added to ensure some amount of stability on the output.
Additionally, a non-populated landing pad (C6) is provided for additional capacitance, if desired.
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MSP430 Low-Pass
Filter DRV2700
www.ti.com PWM and Analog Inputs
5 PWM and Analog Inputs
The flyback configuration on this EVM uses a low-pass (two pole) filtered PWM waveform from the
microcontroller or an analog signal from the user. By default, the DRV2700EVM-HV500 uses the MSP430
PWM input mode. This section describes each input mode in detail and the modifications necessary for
operation of each.
The DRV2700EVM supports two input modes for driving the DRV2700:
•PWM input using MSP430: In this mode, the onboard MSP430 generates a PWM waveform that is
sent through the low-pass input filter to the DRV2700.
•Analog input: An external source supplies an analog waveform to the TP1 header which is sent
through the low-pass input filter to the DRV2700.
Because the low-pass filter will try to pass the DC components of the signal, the PWM/Analog input's
frequency will determine if the filtered signal will still appear AC.
• Low Frequency/AC Mode (< 1 kHz): When below 1 kHz, the PWM signal will hardly be attenuated
such that the majority of the PWM signal will propagate through. This will cause the output to try and
reflect the PWM signal coming from the microcontroller and the output will try to be a square wave.
• Mid Frequency (1 kHz < freq < 20 kHz): When the frequency is set in this range, the PWM signal will
be attenuated but it will still somewhat reflect a PWM signal. This mode can be used for audio tones,
however the output may not be able to drive to full scale, depending on the load capacitance.
• High Frequency/DC Mode (> 20 kHz): As the frequency starts to go higher, the PWM signal will be
greatly attenuated. This will cause the PWM signal to appear DC after this filter. This mode can be
used to drive the output at a DC level which is set by the Boost Voltage Percentage (that is, duty
cycle).
See the scopeshots in Section 3 for example waveforms.
5.1 PWM Input Using MSP430
Figure 10. PWM Signal
When using the DRV2700EVM-HV500 in MSP430 PWM input mode, the onboard MSP430 generates a
PWM signal that is sent through a low-pass filter to the DRV2700. The DRV2700EVM-HV500 is set up to
use this mode by default. Set to the default settings to use this input mode.
If specific waveforms (other than those already on the MSP430) are needed, the firmware can be updated.
To update the firmware, download Code Composer Studio (or a third-party MSP430 IDE) and connect the
DRV2700EVM-HV500 Spy-Bi-Wire to the computer. The TI website offers an MSP430 USB-to-JTAG
hardware interface (MSP-FET430UIF) for updating and debugging MSP430 code.
NOTE: Sample code is also available on the DRV2700 product web page.
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PWM and Analog Inputs www.ti.com
5.2 Analog Input
The following instructions are provided to use an external analog source to drive the DRV2700:
1. Disconnect the MSP430 output pin from the DRV2700 input pins by removing jumper JP1
2. Connect the DRV2700 EN signal:
(a) Use the onboard MSP430 and GUI to control the EN pin by connecting JP3 between EN and MSP
(b) EN the output all the time by connecting JP3 between PU and EN
(c) Use an external control signal by connecting source to the middle header of JP3
3. Connect the analog input signal to TP1 (INPUT). Note, the default input range is from 0–3.3 V (same
as PWM signal). Therefore, if a voltage divider is needed, R21 and R2 can be changed accordingly.
4. Enable the power supply
5. Enable the analog input signal (and EN)
Figure 11 and Figure 12 show waveforms using an external sine wave.
VDD = 5 V C(LOAD) = 22 nF VHV = 0 to 500 V VDD = 5 V C(LOAD) = 22 nF VHV = 0 to 500 V
Input Frequency =
10 Hz Figure 12. 100-Hz Input Signal
Figure 11. 10-Hz Input Signal
16 DRV2700EVM-HV500 High Voltage Piezo Driver Evaluation Kit SLOU407A–April 2015–Revised May 2015
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-
=
G GS(th)
S
DS(Max)
V V
RI
Instantaneous Load Current [mA]
Max Output Voltage [V]
0 1 2 3 4 5 6 7 8 9 10 11
0
60
120
180
240
300
360
420
480
540
600
D001
www.ti.com Output
6 Output
The DRV2700 has an output terminal header for connecting the piezo load.
6.1 Load Selection
The DRV2700 is intended to drive piezo (capacitive) loads. Therefore, there are several key specifications
to consider when choosing a piezo load; such as dimensions, blocking force, and displacement. However,
the key electrical specifications from the driver perspective are voltage rating and capacitance. Figure 13
shows the typical instantaneous maximum load current versus output voltage.
Figure 13. Instantaneous Max Load Current vs Max Output Voltage
6.2 Pulldown Network
The pulldown FET and one or more resistors are used to remove the charge on the high-voltage output
faster than just simply using the feedback resistors. Because the FET must be driven from a comparator,
an NMOS FET must be used. During normal operation, the VDS of the NMOS is subject to any voltage
from approximately 0 V when the FET is on, to the output on the flyback configuration (VHV) when the FET
is off. Therefore, selecting a FET with a VDS breakdown higher than the maximum VHV is required.
Additionally, placing a resistor in series with this FET (on the source side) to limit the current going
through the FET is recommended. This resistor can be sized according to the maximum current allowed
per the data sheet of the FET, such that when current flows through the resistor, it raises the source
voltage and thereby lowers the VGS and shuts the FET off. Using Equation 4 provides a good value of RS
where VGis the VOH of the opamp, VGS(th) is the threshold voltage of the FET and IDS(Max) is the maximum
current allowed through the FET. As an additional measure, one or more resistors can be placed on the
drain and gate side to protect the pulldown FET by minimizing sharp transients that can be coupled to the
other terminals of the FET.
(4)
Because the output voltage will ripple (based on the load current and cap) the threshold at which the
opamp turns on the FET needs to be set effectively. To try and eliminate the need for external references,
two references from the basic circuit configuration are used. The REXT voltage at ≈1.3 V is regulated
internally by the DRV2700; however, it cannot source or sink very much current. Therefore, by connecting
this reference to a high impedance input to an opamp, which draws zero current, this reference can be
used.
17
SLOU407A–April 2015–Revised May 2015 DRV2700EVM-HV500 High Voltage Piezo Driver Evaluation Kit
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+
±
Piezo
Element
VDD
V(REXT)
R(S)
V(Pulldown)
VHV
C(HV)
Output www.ti.com
The second reference voltage is set to about 93% of VFB by creating an additional resistor divider in the
feedback network (VFB2A and VFB2B). This works, such that when the output is rippling during normal
operation, the threshold will not be triggered. However, when the input signal changes so that the output
needs to be discharged, the feedback network will be changed so this reference will become higher than
VREXT and therefore turn on the output FET.
Figure 14. Pulldown Network
Figure 15 and Figure 16 show the different discharge times with and without the pulldown network. Note
the 4x timescale in Figure 16.
VDD = 5 V C(LOAD) = 22 nF VHV = 0 to 500 V VDD = 5 V C(LOAD) = 22 nF VHV = 0 to 500 V
500us/div 2ms/div
Figure 15. With FET Pulldown Figure 16. Without FET Pulldown
18 DRV2700EVM-HV500 High Voltage Piezo Driver Evaluation Kit SLOU407A–April 2015–Revised May 2015
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±
+
VDRV
C1
R3
R21
R2C2
R1
Filter Out
TP1
INPUT
PWM
from uC
JP1
Integrator
First Order Filter
www.ti.com Input Filter
7 Input Filter
The DRV2700EVM-HV500 has an active low-pass input filter to attenuate high frequency PWM signals
coming from the input source. Depending on the input frequency and input voltage, the filter can be
adapted to attenuate any undesired out-of-band content. This section describes the input filter
requirements and the various respective configurations. The filter can be modified by the user, however be
sure that the 3-dB point is no higher than 5 kHz.
See scopeshots in Section 3 for example waveforms.
7.1 First Order Filter
In order to attenuate the high frequency PWM signal, a first order filter was used prior to the integrator to
attenuate the high-frequency components. This RC network has a 3-dB point around 1.75 kHz.
7.2 Integrator
In order to attenuate the PWM signal even further, a non-inverting integrator is used.
Figure 17. Input Filter
19
SLOU407A–April 2015–Revised May 2015 DRV2700EVM-HV500 High Voltage Piezo Driver Evaluation Kit
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IN
1
2
EN
3NC 4
OUT 5
GND
U4
TLV70033DCKR
1000pF
C12
21
SW2
TRIG
0.1µF
C20
10k
R14
P6.0/CB0/A0 1
P6.1/CB1/A1 2
P6.2/CB2/A2 3
P6.3/CB3/A3 4
P5.0/A8/VEREF+ 5
P5.1/A9/VEREF- 6
AVCC1
7
P5.4/XIN 8
P5.5/XOUT 9
AVSS1 10
DVCC1
11 DVSS1 12
VCORE
13
P1.0/TA0CLK/ACLK
14
P1.1/TA0.0
15
P1.2/TA0.1
16
P1.3/TA0.2
17
P1.4/TA0.3
18
P1.5/TA0.4
19
P1.6/TA1CLK/CBOUT
20
P1.7/TA1.0
21
P2.0/TA1.1
22
PJ.0/TDO 23
PJ.1/TDI/TCLK 24
PJ.2/TMS 25
PJ.3/TCK 26
DVSS2 27 DVCC2
28
P4.0/PM_UCB1STE/PM_UCA1CLK
29
P4.1/PM_UCB1SIMO/PM_UCB1SDA
30
P4.2/PM_UCB1SOMI/PM_UCB1SCL
31
P4.3/PM_UCB1CLK/PM_UCA1STE
32
P4.4/PM_UCA1TXD/PM_UCA1SIMO
33
P4.5/PM_UCA1RXD/PM_UCA1SOMI
34
P4.6/PM_NONE
35
P4.7/PM_NONE
36
VSSU 37
PU.0/DP 38
PUR 39
PU.1/DM 40
VBUS
41
VUSB
42
V18
43
AVSS2 44
P5.2/XT2IN 45
P5.3/XT2OUT 46
TEST/SBWTCK 47
RST/NMI/SBWTDIO 48
PAD
U5
MSP430F5510IRGZ
SCL
SDA
VBUS 1
D- 2
D+ 3
ID 4
GND 5
67 89
J1
USB
10µF
C17
J3
10µF
C11
VBUS
0.1µF
C24
VBUS
D+
D-
0.47µF
C23
1
2
3
4
5
6
J4
9.76k
R19
TRIG
Green
D4
511
R15
VIN
3p3
3p3
3p3
3p3
GND
GND
GND
GND
GND
GND
GND
GND GND
0.1µF
C26
GND
1
2
3
JP2
VIN
1
2
3
JP4
VIN
VBUS
0.1uF
C4
IO1
1
IO2
2
GND
3IO3 4
IO4 5
VCC 6
U1
TPD4E004DRY
VBUS
GND
GND
VBUS
VREST
TP2
SBWTDIO
SBWTCK
GND
100
R6
1.0Meg
R12
VBUS
GND
PUR
2
1
SW1
BSL
33
R16
33
R17
D+
D-
1.40k
R8
D+
PUR
0.22µF
C22
0.22µF
C25
1
3 4
2
G
G
12MHz
Y1
ABM8G-12.000MHZ-B4Y-T
10pF
C14
10pF
C15
5.6V
D2
GND
GND
GND
GND
EN_MSP
PWM+_MSP
Power Inputs
Power Routing
MSP430
VPUMP
1
VDD 2
FB 3
GND 4
GND 5
GND 6
SW 7
SW 8
NC
9
VBST
10
VBST
11
PVDD
12
OUT+ 13
OUT- 14
REXT 15
IN-
16 IN+
17
GAIN0
18 GAIN1
19 EN
20
PAD 21
U2
DRV2700RGP
GND
0.1µF
C3
GND
0.1uF
C9
GND
GND
Green
D3
511
R13
EN
3.3k
R7
GND
1
2
3
JP3
VREST
0.1µF
C7
GND
12 43
T1
10µF
C8
1
3
2
D1
GND
GND
GND
EN VDIV
VDRV
VDRV
GND
REXT
GND
HV
VPullDown
PWM+_MSP
22pF
C13
HV
SW3
CL-SB-22B-02T
SW4
CL-SB-22B-02T
RNET2
CNET1
CNET2
RNET1
VDIV VDIV
CNET1
CNET2
CNET1
Rshort = !Cshort
RNET2
VDIV
Rshort = !Cshort
Output Voltage
DRV2700 HV
10k
R5
REXT
VGate
Filter_Out
Filter_Out
0.1uF
C10
GND
D2
C2
B2
BV+
V-
A2
D1
U3B
OPA2376AIYZD
B1
C1
A1
AV+
V-
A2
D1
U3A
OPA2376AIYZD
GND
1000pF
C5
VDRV
VDRV
0
R20
TP3
GND
Ext VIN
5.5V Vmax
1.00M
R9
1.05M
R23
750k
R10
750k
R24
RNET1
VDIV
1.24M
R11
1.24M
R25
i
HV
i
HV
i
HV
i
HV
Selection
DANGER HIGH VOLTAGE
DANGER HIGH VOLTAGE
VDRV
TP1
INPUT
0.047µF
C6
DNP
iHV
8200pF
C21
1
2
J2
392
R18
5.11k
R26
VPullDown
220
R4
VGate
10k
R28
5.1k
R27
5.1k
R22
6800pF
C19
0.01µF
C18
SW3 SW4
Ceq
Lower [nF]
Req
Lower[kΩ]
Ceq
Upper [nF]
Req
Upper[kΩ]HV [V]
Up Up 2.710 5.502 0.022 641.97 159
Up Down 3.717 5.502 0.022 866.20 214
Down Up 4.505 5.502 0.022 1122.30 277
Down Down 8.200 5.502 0.022 2050.00 504
Switch States Equivalent Circuit
GND
1000pF
C2
10k
R3
49.9k
R2 90.9k
R1
69.8k
R21
3900pF
C1
1
2
JP1
Q1
Reference www.ti.com
8 Reference
This section includes the DRV2700EVM-HV500 schematic, PCB layout, and bill of materials.
8.1 Schematic
Figure 18 illustrates the DRV2700EVM-HV500 schematic.
Figure 18. DRV2700EVM-HV500 Schematic
20 DRV2700EVM-HV500 High Voltage Piezo Driver Evaluation Kit SLOU407A–April 2015–Revised May 2015
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