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PGA460-Q1: PGA460-Q1 Multiplexing in Half-Bridge Driver Mode for Mono-static or Bi-static Transducers

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Part Number: PGA460-Q1

PGA460-Q1 Multiplexing in Half-Bridge Driver Mode for Mono-static or Bi-static Transducers

The PGA460Q1HBMUX reference design allows a single PGA460-Q1 device to switch up to either 4, 8 or 16 sensors depending on the specific analog switch/mux part number selected. For this example, the MUX36D04 is used to switch up to four transducers in half-bridge driver mode for either mono-static or bi-static transducers. For mono-static only, the MUX36S08 can be used to switch up to 8 transducers, and the MUX36S16 can be used to switch up to 16 transducers. For bi-static only, the MUX36D08 can be used to switch up to 8 pairs.

The low on-resistance of the MUX36xxx series allows the driver to transmit maximum sound pressure level at the maximum supported transducer driver output of 30V at the PGA460's OUTA and OUTB pins. Depending on the high side voltage of the half-bridge driver, the current limiting resistor (mono-static schematic's R4 and bi-static schematic's R9) can be further reduced from 287Ω, since this default value of 287Ω is intended to limit the transient current through the mux channel's to 30mA at the maximum voltage of 30V. 30mA is the maximum rated channel current for the MUX36xxx series. For instance, a high side driver voltage of 7 to 10V does not require any (or very little) current limiting resistance at the drain of the external pMOS since the transient current through the transducer is already at or below 30mA.

Optimizing the value of the current limiting resistance will be specific to the transducer and external pMOS characteristics. Too much current limiting resistance will impact the RC time constant, load transducer driving rise time, and yield as a loss of peak performance. However, too little can cause a current overshoot condition through the mux's channels, and potentially damage the mux in the long term. Transducer's typically do not require a large amount of driving current, hence the 30mA limitation is acceptable. The peak-to-peak driving voltage, driving frequency, and signal integrity/shape is more crucial in generating maximum sound pressure level.

Mono-static Multiplexing Schematic:

Bi-static Multiplexing Schematic:

Akeem Whitehead // Texas Instruments // ASC-SENSING-SSC // Applications Engineer
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