PGA460: [PGA460TPWR] Circuit Review Request

Hi MJ,

I have the following comments:

1. I would remove the 3.3 V pull-up resistor on the IO pin. The IO pin is actually referenced with respect to VDD_Tx instead of VDD_3.3 V.
2. You can leave the pull-up resistor on the TXD pin; however, I would not populate the pull-up resistors on the SCLK and RXD pins.
3. Since you appear to be using 3.3 V logic, I recommend populating R80 and not populating R72.
4. I’d add a capacitor in parallel to the secondary of the transformer. This capacitor will help reduce the ring decay time to reduce the minimum distance that you can sense. The actual value of this capacitor will depend on your system.  We recommend iteratively trying different capacitor values to see which option reduces the ring time, as is mentioned in Section 4.4.2 of the below application note: https://www.ti.com/lit/an/slaa732a/slaa732a.pdf
5. I recommend adding a Schottky diode between the power supply and the VPWR pins, similar to diode D1 that is shown in Figure 136 of the datasheet. I’d also recommend adding the R_INP resistor that is also in this figure.
6. In the schematic, I see that C74 and C76 have the same capacitor values; however, I would expect that these capacitors would have different values since they have different calculation formulas. Table 101 provides the formulas for calculating these two capacitors based on the frequency of your transducer.

Regards,

Mekre