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PWM, Analog, and Single-Ended Inputs
15
SLOU403C – March 2015 – Revised June 2018
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Copyright © 2015–2018, Texas Instruments Incorporated
DRV2700EVM High Voltage Piezo Driver Evaluation Kit
5
PWM, Analog, and Single-Ended Inputs
The DRV2700 requires a low-pass filtered PWM waveform, an analog signal or a single-ended input to
drive capacitive loads. By default, the DRV2700EVM uses the MSP430 PWM input mode with a low-pass
filter. This section describes each input mode in detail and the modifications necessary for operation of
each. See
Filtering and Adapting PWM Waveforms
for more details on adapting the PWM waveform using
a low-pass filter.
The DRV2700EVM supports four input modes for driving the DRV2700:
•
PWM (AC coupled) 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.
•
PWM (AC coupled) input using AIN:
An external source supplies a PWM waveform to the EXTIN
header which is sent through the low-pass input filter to the DRV2700.
•
External analog (AC coupled) input:
An external source supplies an analog waveform (sine wave) to
the IN+ and IN– header. The low-pass input filter can be removed in this case.
•
Single-ended (DC coupled) input:
A DC input signal can be used to drive the output in a steady
state.
5.1
PWM (AC Coupled) Input Using MSP430
Figure 9. PWM Signal
When using the DRV2700EVM in MSP430 PWM input mode, the onboard MSP430 generates a
differential PWM signal that is sent through a low-pass filter to the DRV2700. The DRV2700EVM is setup
to use this mode by default. Set to 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 SpyBiWire 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.
5.2
PWM (AC Coupled) Input Using AIN
The PWM input mode can be used with an external processor or PWM source. The PWM signal is a
carrier wave (duty-cycle modulated) at a frequency much higher than the analog signal it represents. The
PWM input mode can be used with an external processor or PWM source.
To use an external PWM source to drive the DRV2700, follow these instructions to modify the board:
1. Disconnect the MSP430 output pins from the DRV2700 input pins by removing jumpers JP5 and JP6
2. Depending on the input source, follow the instructions in the
Filtering and Adapting PWM Waveforms
section to adjust the input filter.
3. Connect DRV2700 control signals:
a. Use the onboard MSP430 and GUI to control the EN, GAIN0, and GAIN1 pins.
b. Use an external controller or jumpers to control the EN, GAIN0, and GAIN1 pins.
4. Connect the positive terminal of the input signal source to AIN+ and the negative terminal to AIN–
5. Enable the power supply
