PGA450-Q1: selection of component between PGA450-Q1 or PGA460-Q1

Hi Shyam,

I will recommend the PGA460-Q1 for this park assist application because the PGA460 offers superior performance, lower cost, smaller size, and easier programming than the PGA450-Q1. 

The PGA460-Q1 uses an alternative interface to the LIN called One-Wire UART (OWU) on the IO pin. OWU is a simplified version of the LIN interface, and excludes items such as the break field and much of the other LIN padded frames. The PGA460's OWU bus can support up to eight devices, each with its own unique ID. The unique ID of each PGA460 is stored in the 3-bit UART_ADDR field in the EEPROM memory. The OWU UART_ADDR substitutes the traditional LIN's NAD. Because many ECUs use a UART port to enable LIN, the same UART port can be used to enable OWU on the PGA460. The OWU interface uses the same command and packet structure as the PGA460's standard UART.

Here is more information on the two automotive-centric one-wire interfaces available on the PGA460, both use the IO pin:

• Time Command Interface (TCI)
• One-Wire UART (OWU)

TCI:

The TCI interface is a low BW interface for reading and writing registers; however, during typical time-of-flight operation, the TCI pin toggles in real-time when an echo is detected, meaning you get the TOF data faster than any other interface. The TCI interface can only be used in a star topology due to the lack of addressing. The TCI interface will also require an intermediate transceiver between the PGA460 and ECU, so each PGA460 device will need a dedicated GPIO pair from the ECU. Of course, you can multiplex the GPIO signals to minimize the number of allocated GPIOs if you do not intend on simultaneously bursting/listening on multiple PGA460s. TCI is mainly suggested for solutions that require real time TOF data. The idea is that you only read/write registers during start-up for device configuration, and in other special cases (i.e. diagnostic checks or device reconfiguration), so the bulk of the device is operating in the real time TOF mode.

OWU:

The OWU mode is more flexible, and is available as a simplified alternative to the LIN interface. You can leverage the PGA460’s address to create a bus topology to only use one UART port from the ECU to bus up to eight PGA460s. In your case, I suspect you will have two UART ports: one for the front bumper and one for the rear bumper. Though the PGA460 does not support daisy chain addressing directly, there are external means of enabling daisy chaining (see Appendix-A below). The primary difference is that in the OWU mode, the device must wait the entire duration of the record length cycle before reading back the TOF results. This means the data response is not real-time, so the OWU approach is for less time sensitive applications. For example, if the maximum detectable range requirement is 5m, then the record cycle length is 32ms, so even if an object is detect very close to the sensor, e.g. at 4ms in time, the device has no means of indicating this early detection, and the user must always wait 32ms to read back the ultrasonic measurement results. An additional benefit to using the OWU mode is that the TOF is computed by the PGA460 as a 16-bit result in 1us resolution, while also being able to provide the echo amplitude and width details. The TCI mode can only provide the echoes rising/falling edges, and requires the ECU to compute the TOF based on these edge captured deltas. I typically recommend OWU for most automotive single wire applications because it is more intuitive, and leverages more of the PGA460’s features. It can only support up to 115.2kBaud for fast read/writes. You will also need a LIN transceiver between the PGA460 IO bus and ECU UART pins.

The UART (2-pins) and USART/SPI (3-pins) low-voltage interfaces are intended to be used for commercial/industrial applications, but can be leveraged for automotive if preferred. These are more standard, and can be directly interfaced to the PGA460 bus from the ECU. The cost of using a one-wire interface versus the increased cable count for the low-voltage interfaces is an exercise you will need to perform. I suspect the transceiver may be a lower cost solution versus a 2 or 3 pin bus being routed to each of the bumpers.

Appendix-A:

If you are able to pre-program the UART_ADDR (bus address) of each PGA460 module before installing the module onto the OWU bus, they will be able to differentiate and independently read/write between each module. However, in the case auto-addressing of each module is required, such that multiple fresh PGA460s are installed on the bus (each will have a default UART_ADDR of 0), below are two auto-addressing options: