# PDu100B Miniature Piezo Driver

The PDu100B is a complete miniaturized power supply and linear amplifier for driving piezoelectric actuators. The PDu100B provides variable gain and offset, switchable voltage ranges, and the choice between unipolar and bipolar inputs and outputs. The PDu100B can drive two-wire piezoelectric actuators and benders up to +/-100 V and three-wire piezoelectric benders and stack actuators up to +100 V. Applications include piezoelectric valves, motors, pumps, MEMs, and ultra low-power positioning and manipulation systems.

The PDu100B is protected against current overload and excessive temperature. A shutdown pin is also provided that reduces supply current to 1 mA when pulled low. The PDu100B can be used as a stand-alone module or mounted to a base with four M2.5 threaded spacers. The PCB mounting version (PDu100B-PCB) is supplied with headers for direct mounting on a host motherboard.

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### Compatible Actuators

 Stack Actuators 60V, 100V Plates and Tubes Up to +/-100V Two Wire Benders Up to +/-100V Three Wire Benders 0 to 100V with 100V bias

### Specifications

 Power Supply 3 V to 5.5 V Max Unipolar Output +60 V +90 V +100 V Max Bipolar Output +/-60 V +/-90 V +/-100 V RMS Output Current 89 mA 60 mA 33 mA Average DC Current 40 mA 18 mA 15 mA Power Bandwidth 5.3 kHz 3.5 kHz 3.2 kHz Peak Output Current 100 mA Signal Bandwidth 60 kHz (unloaded) Dimensions 39 x 25 mm (1.5 x 1 in) Weight 5.5 g (0.2 oz) Gain 27.5 V/V Unipolar Input Z 100 kOhm Biipolar Input Z 20 kOhm Input Offset +/-100 mV Load Capacitance Unlimited Overload Protection Thermal and current Noise 70mV RMS (10uF Load) Environment -40 to 70 C (-40 to 158 F) Quiescent Current 25 mA (1 mA in Shutdown)

### Operation

A power converter generates a unipolar or bipolar supply. The output voltage range is controlled by the voltage selector jumpers. The amplifier has a gain of 20 and an input voltage range of +/-10 V. The load is connected directly to the high-speed output (V1) or through a filter (V2) which reduces the noise and bandwidth. In most applications, the V2 output is recommended.

When the amplifier is configured for 200V operation, a 200V bias supply is enabled for bimorph bender applications.

### Configuration

The PDu100B can be configured to suit a wide variety of applications. The output voltage range is selected by Switch 1 (S1) as shown below.

 S1.1 S1.2 Unipolar Range Bipolar Range On On 100 V +/-100V On Off 90 V +/-90V Off On 70 V +/-70V Off Off 60 V +/-60V

Output voltage range configuration

The input type can be configured to either unipolar or bipolar with Switch 2 (S2), as shown below.

 Input Type S2.1 S2.2 Input terminal Input Range Unipolar On Off Vup 0.5 Vs +/- 1.8V Bipolar Off On Vbp +/- 3.6V

Input type configuration

The overall system gain is determined by the configuration of the input and output. The possible combinations are listed below.

 Input Type Output Type Gain Input Range Output Range Unipolar Unipolar 27.5 0.5 Vs +/- 1.8V 100 V Unipolar Bipolar 55 0.5 Vs +/- 1.8V +/-100 V Bipolar Unipolar 13.75 +/- 3.6V 100 V Bipolar Bipolar 27.5 +/- 3.6V +/-100 V

System gain and voltage range

Both outputs are biased at approximately half the HV bus voltage $V_{HV}$, e.g. 50 V with a 100 V range. The output voltage equations are listed below.

 Input Type Output Type Output Equation Unipolar Unipolar $27.5 \times \left(V_{up}-\frac{V_S}{2} \right) + \frac{V_{HV}}{2}$ Unipolar Bipolar $55 \times \left(V_{up}-\frac{V_S}{2} \right)$ Bipolar Unipolar $13.75 \times V_{bp} + \frac{V_{HV}}{2}$ Bipolar Bipolar $27.5 \times V_{bp}$

System gain and voltage range

The HV bus voltage (and bias output) can be varied by 10% using the trimmer R15. The gain and output voltage ranges can be customized by contacting info@piezodrive.com.

### Offset Voltage

The trim pot R15 adjusts the DC offset voltage, which has a range of +/- 250 mV.

### Output Current

The maximum RMS and average DC output current for each voltage range is listed below. The average DC current is the average current flowing in either the positive or negative direction. For a sine wave, the average DC current is related to the RMS current by

$$I_{av}=\frac{\sqrt{2}}{\pi} I_{rms}$$

 Voltage Range RMS Current Average Current 60 V 89 mA 40 mA 70 V 67 mA 30 mA 90 V 60 mA 18 mA 100 V 33 mA 15 mA

Maximum RMS and average DC output current

For periods less than 100 us, output currents of approximately 100 mA are possible. This is useful for achieving small, high-speed step changes in the output voltage.

### Power Bandwidth

#### Calculate Power Bandwidth (+/-100V Range)

The output slew-rate of the PDu100B is 1 V/us. Therefore, the maximum frequency sine-wave is

$$f_{max}=\frac{1 \times 10^6}{\pi V_{L(p-p)}} .$$ The power bandwidth for each voltage range is listed below

 Voltage Range Power Bandwidth 60 V 5.3 kHz 70 V 4.5 kHz 90 V 3.5 kHz 100 V 3.2 kHz

With a capacitive load, the power bandwidth is limited by the maximum output current. For a sine wave
$$f_{pwr}=\frac{I_{av}}{V_{L(p-p)} \pi C_L } .$$ The power bandwidth for a unipolar load is listed below. For a bipolar load, the power bandwidth is halved since the voltage range is doubled.

 Load (uF) 60 V 70 V 90 V 100 V 0.01 5300 4500 3500 3200 0.03 5300 4500 2100 1500 0.1 2100 1300 630 470 0.3 700 450 210 150 1 210 130 63 47 3 70 45 21 15 10 21 13 6.4 4.8 30 7.1 4.5 2.1 1.6

Power bandwidth versus voltage range and capacitance (in Hz)

In the following figures, the maximum peak-to-peak voltage is plotted against frequency for a range of capacitive loads.

### Signal Bandwidth

The unloaded small signal bandwidth of the PDu100B is approximately 60 kHz. With a capacitive load, the signal bandwidth is predetermined to be ten times greater than the power bandwidth, that is

$$f_{bw} = \frac{1}{1700 C_L} .$$ The small signal bandwidth for a range of load capacitances is plotted below and listed in the following table.

### Noise

The output voltage of the PDu100B contains switching noise from the boost converter and random noise from the high-voltage amplifier. With a 5 V supply and 100 V output range, the measured noise (Fluke 189) is listed below.

 Load Capacitance (uF) Signal Bandwidth Noise (RMS) 10 nF 30 kHz 550 mV 30 nF 19 kHz 450 mV 100 nF 5.9 kHz 350 mV 300 nF 1.9 kHz 280 mV 1 uF 590 Hz 190 mV 3 uF 190 Hz 120 mV 10 uF 59 Hz 70 mV 30 uF 19 Hz 50 mV

Signal bandwidth and noise

The output voltage noise can be reduced by using an output resistance to reduce the bandwidth. The correct circuit configurations for different applications are illustrated below.

To determine the output resistance required for a particular noise level, the required bandwidth should be selected from Figure 9 below. The correct resistance can then be calculated from

$$R_O = \frac{1}{2 \pi f_{bw} C_L } – 270 ,$$

The noise measurements are performed with a static input voltage. When current is drawn from the output, the ripple will increase due to action from the boost converter.

### Power Dissipation

With a capacitive load, power dissipation is the product of supply voltage and average current, that is

$$P_D = V_S \times I_{S(av)}$$ When operating at full power bandwidth, the worst-case power dissipation is approximately 2.5 W. The thermal impedance of the PDu100B from junction to ambient is 30 K/W. Therefore, the maximum temperature rise is approximately 75 degrees C above ambient.

If full-power operation is required at ambient temperatures exceeding 50 degrees C, a 21 mm heat-sink is recommended on the bottom surface. This also requires the connectors to be mounted on the opposite side of the PCB. The order code for a device with unmounted connectors and heat-sink kit is PDu100B-HS.

### Enable / Shutdown

The Enable pin can be pulled low to disable the amplifier and reduce the quiescent current to 1 mA. It can be driven by a logic output or an open collector output. The recovery time after a shut-down is 2 ms.