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PGA460-Q1: Two-Wire Ultrasonic Sensor Module

Akeem Whitehead
Mastermind 27940 points
Part Number: PGA460-Q1
Other Parts Discussed in Thread: PGA460

PGA460-Q1 Two-Wire Ultrasonic Sensor Module (TWSM)

The PGA460Q1TWSM  is a variant of the PGA460-Q1 small form factor reference design for systems which require a two-wire ultrasonic sensor module solution, whereby one-wire interface data is transmitted over power. This module only requires VPWR_IO and GND pins. Here is the PGA460Q1TWSM schematic:

where the add-on components from the original small form factor solution required enable the two-wire interface are as follows:

    • R2 = serial current-limiting supply resistor (alternative can be an inductor for EMC purposes)
    • D1 = reverse polarity protection diode
    • C5 = reservoir capacitor for VPWR (prevents under-voltage condition)
    • C6 = blocking supply capacitor (optional)
    • R6 = serial resistance for IO line (optional; placeholder for additional resistance or inductance)
    • C14 = capacitor for IO line (optional)

In this schematic, two electrolytic capacitors are present. If the system does not require R1 (serial resistor for transformer’s center-tap), then a single electrolytic can be shared by both VPWR to save on components-count and cost. However, the TWSM then relies on R2 to limit the in-rush current to the center-tap's charge capacitor, which may cause VPWR to droop during burst.

For automotive demonstration purposes, the PGA460-Q1 EVM’s IO pin at J6-2 is used to emulate a Body Control Unit (BCU) VPWR_IO connection. The user is required to desolder the EVM's shunt at R15 to prevent TCI/OWU communication with the PGA460 IC on-board the EVM. Also, reducing the EVM’s IO pull-up at R20 from 1kOhm to 0.1kOhm is required to allow a sufficient amount of current to supply the TWSM.

PGA460-Q1 EVM modifications:


After applying the aforementioned modifications to the EVM, and connecting the TWSM to the EVM, the example TCI results are as follows:

Read temperature measurement:

This example shows a very basic TCI read of a single register.

Write P1 threshold times and levels:

This examples shows that a very long TCI write command will cause the supply and logic-high reference to slightly droop over time for long transmit commands.

Preset 2 Burst & Listen (18 pulses at 400mA)

This example shows that the supply and TCI voltages are maintained, even after a high power transducer excitation. The measurement is showing the detection of the ceiling at 2m.

Read Echo Data Dump Memory (three times sequentially)

This example illustrates the worst case read example. Here we are showing the longest TCI read command (index 12 echo data dump value) executed three times. The supply droops down to 7.444V.

Due to the two forward voltage diode drops from the EVM’s D11 and the two-wire module’s D1, and the current limited IO master on the EVM, the static supply voltage is not 12V as sourced from the main PSU, but at 9~10V at VPWR of the TWSM. Depending on how the customer intends to test the TWSM (i.e. with an actual BCU), the amount of voltage drop can be reduced/controlled.

The GUI can be used to read and write the TWSM’s registers exclusively through the Interface Mode --> IO TCI page. Here I was able to confirm that the oscilloscope activity matched the GUI display:

TI will continue to optimize and simplify the schematic, but the presented means of experimentation is a proven starting point to for any interested user.