The DC-coupled referenced to V_DD input is used in applications when the user might need to drive the output at a constant DC level in an on-off implementation. A typical application for this configuration is for piezo pneumatic valves. A benefit to this application circuit is that all of the inputs, including power, are at a very low voltage while keeping the high-voltage piezo load separated. Additionally, all that is required is the V_DD input. This feature allows easy implementation into systems and to help separate or isolate the high voltages loads from the critical controls.

As mentioned in the previous section, piezoelectric materials have a certain voltage that debias the piezo phenomenon. This configuration protects the piezo from negative voltages because the input is always positive.

Figure 8-14 DC-Coupled Referenced Input

This application circuit can also be altered to only use the boost as shown in Figure 8-15. The benefits of altering this circuit is that it requires less components and has better power efficiency because no power is used in the amplifier. The drawback is that ripple occurs on the piezo element and the fall time of the output is longer because it is drained based on the RC time constant on the BST node.

Figure 8-15 Boost Driving Piezo