Test Report
July 2017
1
PMP15034 Test Results
System Description
A piezoelectric sounder is a loudspeaker that uses the piezoelectric effect to generate sound. It is widely used in
the application where sound volume and high pitch are more important than sound quality, such as toys, air
conditioner, microwave oven and alarm equipment.
The piezoelectric sounder normally required a 1-KHz to 5-KHz rectangular voltage to operate. The sound press
mainly depends on the amplitude of the driving voltage. The higher driving voltage, the higher sound press will be.
For example, the PKM13EPYH4002 from Murata requires 0-V to 30-V or +15-V to
−15-V rectangular voltage. The
power supply in these applications could be two cell alkaline battery, lithium-ion battery or 3.3-V, 5-V power rail,
which is much lower than the target voltage. Therefore, a high performance, simple boost converter TLV61046A
is required for this application.
TLV61046A is 1.8-V - 5.5-V input, up to 28-V output, full integrated boost converter. It integrates low side
MOSFET, high side rectifier diode and the isolation MOSFET. The isolation MOSFET disconnects the pass-
through path between input and output when the device is disabled. This function helps to reduce the battery
power loss when the piezoelectric sounder doesn’t work.
Based on TLV61046A, the reference design introduces two driving circuit of piezoelectric sounder. With PWM
signal from MCU, one circuit provides rectangular wave driving voltage between 0-V and 28-V; the other circuit
provides ±15-V rectangular wave driving voltage.
The block diagram of the 28-V driver circuit is shown in Figure 1. The output voltage of the TLV61046A is set to
28V. A PWM signal from MCU drives Q1 to control the voltage across the piezoelectric sounder LS. When PWM
signal is logic high, the Q1 turns on, so 28V is applied to LS. When PWM signal is logic low and Q1 turns off, the
LS is discharged by the resistor in parallel. The frequency of the PWM signal should be equal to the
recommended frequency of the sounder. The duty of the PWM should be as low as possible to reduce the power
loss when the sound press is acceptable.
1.8V~5.5V
TLV61046A
Boost Converter
VIN
GND
VOUT
PWM
28V
GND
U1
Q1
LS
Figure 1: Block Diagram of the 28-V Driver Circuit
The block diagram of ±15-V driving circuit is shown in Figure 2. The output of the TLV61046A is set to 15V. An
additional charge pump circuit doubles the output voltage to approximately 30V. When Q1 turn off and Q2 turn on,
the voltage according the sounder LS is 15V; when Q1 turns on and Q1 turns off, the voltage according LS is -
15V. The frequency of driving voltage follows the PWM input from MCU. By modifying the feedback divider of the
TLV61046A and selecting proper Q1, Q2, this circuit supports ±28 V for the sound. The resistor in parallel with LS
can discharge the voltage to zero after the boost converter is disabled.
