PGA460: Schematic validation for the PGA460

Hi Adrien,

Reviewing the principal characteristics of your sensor and use-case:

1) The PGA460-Q1 is compatible with frequencies operating between 30-80kHz and 180-480kHz, so your 75kHz transducer can be used.

2) Because the PGA460 can only drive a 15V center-tap at 500mA, and the turns ratio of most center-taps are limited to 1:1:10, your external driver implementation is a feasible workaround to drive your transducer closer to 1000V. Keep in mind that the OUTA/B pins are limited to 30V, so your high-side driver voltage from the linear regulator should not exceed 30V. Since you are able to control the linear regulator's output, you have effectively created an SPL output control, which is the idea of the driver current limiting if your were using OUTA/B to drive the transformer directly.

3) A 4 to 5m max range is typical for automotive ultrasonic applications. However, most automotive customers are using transducers in the 40~60kHz range. I do not have experience using a +60kHz transducer, but I suspect a 75kHz should be able to reach your intended range given the beam pattern will also be more focused in the forward facing direction due to the higher frequency.

4) The -40°C to +75°C is supported by the PGA460, but beware that the transducers behavior may change at the low or high temperature ends. The behavior may change as an increase to the ring-decay time, center-frequency, or external passives for transducer-transformer matching. It looks like you only have a resistor in parallel to the transducer. It may be worth adding a tuning capacitor that your can enable or disable based on the optional temperature decoupling feature of the PGA460. The PGA460 datasheet discusses temperature decoupling in more detail if you are interested.

5) If your 75kHz transducer is a closed-top type transducer, then you should be ok to operate in an automotive type environment to protect against water, dust, dirt, and other airborne debris.

I've reviewed your schematic, and have no major concerns. Observations and considerations:
1) The TEST pin is pulled high, so your SPI is 5V logic level referenced.
2) The majority of PMOS FETs have a max V_GS rating of +/-20V. This means you will be limited to a linear regulator output voltage of 20V, unless your PMOS has a higher than usual V_GS rating. This may not be an issue depending on the targeted output range of your linear regulator output (I don't know the value of your +BAT_PRO).
3) Consider adding a placeholder for a tuning capacitor in parallel to the transducer. Alternatively, consider adding the tuning capacitor controlled by the DECPL pin through a low-side FET as shown in the temperature decoupling schematic in the datasheet.

Since you are using the OUTA/B as gate drivers, your PGA460 will last longer than a traditional use-case since you are only sinking V/1k (6~30mA) through the internal FETs (which anticipate 500mA during our stress testing). You will likely need to replace the transducer before the PGA460 device. The PGA460 was designed with the minimum intended lifespan to that of a typical automobile.