Boost Converter
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12
SLOU403C – March 2015 – Revised June 2018
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Copyright © 2015–2018, Texas Instruments Incorporated
DRV2700EVM High Voltage Piezo Driver Evaluation Kit
The GUI is broken up into two sections:
Standard Drive
and
Audio Drive
. The
Standard Drive
utilizes
changing the frequency and duty cycle of the PWM signal and is intended for easy prototyping. The
Audio
Drive
tab is for showcasing the DRV2700 as a Piezo buzzer/speaker. On both tabs, the sections are
intuitive, however, the following sections are worth describing:
•
Gain Settings and Boost Chart:
After changing the gain and clicking the
Set
button, the MSP430
changes the G0 and G1 GPIO therefore changing the gain of the DRV2700. The chart then updates to
reflect the recommended voltage ranges by
not highlighting them
.
•
Output Timing:
This button has 3 different modes:
Continuous
,
Pulsed
, and
Single
. These modes help
with a timed EN signal.
•
Duty Cycle:
This allows control of the power that gets through the DC blocking input filter.
Duty Cycle
can be thought of as an amplitude control. Additionally, the PWM signal can be connected through
external wires using JP5 and JP6 headers to IN+ and IN–, in order to control the output.
•
Note Generator and Simple Piano:
The DRV2700 is capable of also driving piezo loads used in
many alarms and buzzers. To sample this, the simple piano sends the corresponding frequency of the
notes when pressed. If a series of notes and/or frequencies with specific timing is desired, the note
generator can be used in the format of “[Note],[TimeOn],[TimeOff]” as shown in
Figure 7
. The note
format is A–G (including sharps “#” but not flats “b”) followed by the octave, and the frequency is in Hz
rounded to the nearest integer. Some examples include: A4, C#5, E5 (or 659), and so forth. All time
inputs are based in milliseconds.
See
Figure 13
for a diagram of the input configuration.
4
Boost 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. The
power FET and power diode of the boost converter are both integrated within the device to provide the
required switching while minimizing external components. Additionally, the boost voltage output (BST) can
be easily fed into the high-voltage amplifier through the adjacent pin (PVDD) to help minimize routing
inductance and resistance on the board.
Before connecting the load, ensure the load is rated for the current boost voltage setting.
See
Boost Voltage Setting Resistors
for more information on how to set the boost voltage.
