I'm looking how to easily drive ultrasonic transducer Prowave 500MB120 or similar from MSP430. I found TI: Ultrasonic Distance Measurement With the MSP430 and AnalogDevices-Ultrasonic Distance Measurement CN-0343 application notes. Both solutions use complement MOSFET output,
CD4049 (5-18V, cca 20mA) vs.
ADP3629 (9.5-18V, 2A). Because at least for testing purposes voltage <9V is advantage I'd prefer
CD4049 option which is also recommended in Prowave sheets. Transducer impedance is 800 ohm, I believe current is in tenths of mA, am I right ?
I plan substitute it with
CD4041 which has almost symetric max.source/sink output current.
I need battery powered circuit so low-power consumption in sleep mode is essential. How to do it ?
1) I don't think I can leave MCU output in Hi-Z state because it's against TI's recommendation force HI or LOW output when unused, not Hi-Z!. And probably the same problem with output FETs.
2) when I force HI or LO with
CD4041 then there is full DC voltage (Vcc-GND) on transducer (with serial capacitor). What is supposed quiescent current ?
3) drive from 2 complementar MCU timer outputs. It allocates 2 timers and MCU pin but in sleep mode both output can be forced to HI (or LO), i.e. transducer is not powered (Vcc-Vcc or GND-GND). Also
CD4041 cannot be used as well as there is internal invertor.
Regarding receiver part I wonder how to sleep easily amplifiers as they have no SHUTDOWN pin. I plan 2 stage amplifier connected to MSP comparator input. I found some ICs from
TLV277x series are produced also with shutdown but they are rare in Europe, alternatively
I have an idea powering amplifiers from dedicated MSP pin with decoupling capacitor, i.e. on/off it as needed. 3V is ok, available current should be sufficient too. Is it feasible this way without adding MCU noise or have I overlooked some issue... ?