Texas Instruments PGA460-Q1 User manual

PGA460-Q1
TIDA-01597
Transformer
MA58M
F14-7N
PGA460-Q1
Transformer
MA58M
F14-7N
PGA460-Q1
Transformer
MA58M
F14-7N
TIDA-01597
TIDA-01597
Local ECU/Main ECU
IO
12 V Load Dump Protected
GND
TX
RX
SN65HVDA100-Q1
OWI Transceiver
MSP430F5529
Launchpad
CC2640F128
1
TIDUDO4–May 2018
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Automotive Ultrasonic Sensing Module Reference Design for Park Assist
TI Designs: TIDA-01597
Automotive Ultrasonic Sensing Module Reference Design
for Park Assist
Description
This reference design provides hardware architecture
for a Park Assist System (PAS) using three highly-
integrated, system-on-chip (SoC) ultrasonic transducer
drivers. These ultrasonic transducer drivers have an
integrated signal conditioner with an advanced digital
signal processor (DSP) core. Using these integrated
features, object detection from 25 cm to 2.5 m is
achieved. The distance data is sent over a one-wire
interface (OWI) to a local electronics control unit
(ECU) where the data can be aggregated and
processed. The sensor initialization, object detection
algorithm, and software described in this design guide
provide a basic framework to help engineers working
on PAS for automotive or collision avoidance.
Resources
TIDA-01597 Design Folder
PGA460-Q1 Product Folder
ASK Our E2E Experts
Features
• Combines Three PGA460-Q1 Devices to Detect
Objects From 25 cm to 2.5 m
• Provides System Diagnostic Information
• Circuitry for Level USART and TCI Interface Option
Included
• 22-mm Diameter Solution Size
Applications
• Ultrasonic Park Assist
• Collision Avoidance
An IMPORTANT NOTICE at the end of this TI reference design addresses authorized use, intellectual property matters and other
important disclaimers and information.

PGA460-Q1
TIDA-01597
Transformer
MA58M
F14-7N
PGA460-Q1
Transformer
MA58M
F14-7N
PGA460-Q1
Transformer
MA58M
F14-7N
TIDA-01597
TIDA-01597
Local ECU/Main ECU
IO
12 V Load Dump Protected
GND
TX
RX
SN65HVDA100-Q1
OWI Transceiver
MSP430F5529
Launchpad
CC2640F128
System Description www.ti.com
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Automotive Ultrasonic Sensing Module Reference Design for Park Assist
1 System Description
To detect an object behind the car during reverse motion, a park assist system should cover the entire
rear side and blind spots. For the low-cost implementation in this reference design, a three-sensor system
is used. However, the same concept can easily be extended to four sensors.
For PAS, the maximum detection range requirement from the vehicle can extend up to 1.5 m or 2 m. In
addition, it is also important to be able to detect objects at very close distances, less than 20 cm from
vehicle. Object distance information is then sent over OWI to an ECU where data is aggregated.
In the case of the rear sonar, two to four transformer-driven ultrasonic sensors are mounted on the rear
bumper to detect an obstacle up to 2 to 2.5 m away. The main characteristics of ultrasonic sensors for
rear sonar are directivity, ringing time, sensitivity and sound pressure. Directivity of an ultrasonic sensor
corresponds to the size and shape of the vibrating surface (that is, emitting the ultrasound) and the
frequency at which it vibrates.
Being an automotive application, it is also important to have a solution which can provide sensor
diagnostic information. The solution should also detect and report failures of individual sensors for
passenger safety. Here, the PGA460-Q1 device can provide sensor, supply, and transceiver diagnostics.
2 System Overview
2.1 Block Diagram
Figure 1. TIDA-0597 Block Diagram

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2.2 Design Considerations
Table 1 and Figure 2 show the average dimensions of a car. The width of an average car is within 1.5 m
to 1.75 m. As mentioned before, to detect an object behind the car during reverse motion, the park assist
solution should cover the entire rear side and blind spots.
Table 1. Example Dimensions of Car
Dimensions (m)
Length 3.85
Width 1.7
Height 1.53
Ground Clearance 0.17
Figure 2. Car Dimensions
As an example of an actual system, consider a car that is 1.7 m wide. Referring to Figure 2,L1+L2+L3
+ L1 = 1.7 m. If L1 = 0.1 m, then the distance between the adjacent sensors, L2 = L3 = 0.75 m and the
approximate height of sensor placement is H = 0.5 m to 0.8 m.
Figure 3 represents placement of three sensors S1, S2, and S3, which are 0.75 m apart, along with
various zone boundaries drawn to the scale. Boundaries of various zones are represented with different
colors with the intent to generate appropriate alerts for the driver.

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Automotive Ultrasonic Sensing Module Reference Design for Park Assist
Figure 3. Sensor Placement Diagram
3 Highlighted Product
3.1 PGA460-Q1
This design meets all the requirements previously mentioned using TI’s Automotive Ultrasonic Signal
Processor and Transducer Driver, PGA460-Q1. The PGA460-Q1 device is a highly-integrated system on-
chip ultrasonic transducer driver and signal conditioner with an advanced DSP core. The device has a
complimentary low-side driver pair that can drive a transducer either in a transformer-based topology
using a step-up transformer or in a direct-drive topology using external high-side FETs. The transformer-
driven solution is examined here to meet minimum and maximum range requirement for PAS.
The PGA460-Q1 device can receive and condition the reflected echo signal for reliable object detection.
This feature is accomplished using an AFE consisting of a low-noise amplifier followed by a programmable
time-varying gain stage feeding into an ADC. The digitized signal is processed in the DSP core for both
near-field and far-field object detection using time-varying thresholds.
The main communication with an external controller is achieved by either a time-command interface (TCI)
or a one-wire USART asynchronous interface on the IO pin, or a CMOS-level USART interface on the
RXD and TXD pins. This system is implemented using a one-wire USART interface to keep the BOM cost
and BOM count low.
The PGA460-Q1 device can be put in ultra-low quiescent current low-power mode to reduce power
consumption when not in use and can be woken up by commands on the communication interfaces. The
PGA460-Q1 device also includes on-chip system diagnostics which monitor transducer voltage during
burst, frequency, and decay time of the transducer to provide information about the integrity of the
excitation as well as supply-side and transceiver-side diagnostics for overvoltage, undervoltage,
overcurrent, and short-circuit scenarios.

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Automotive Ultrasonic Sensing Module Reference Design for Park Assist
4 System Design Theory
A PAS solution can be divided in 3 subsections – Ultra sound sensor (also known as Piezo sensor),
sensor driver and receiver circuit (PGA460-Q1), and communication interface for multiple sensors with
ECU. This section covers details of each system (or sensor?) here.
4.1 Ultrasound Sensor and Characteristics
PAS controls steering, acceleration, and braking automatically, based on the parking zone and location
information gained from the ultrasonic sensor, to achieve parallel parking and garage parking. In the case
of the rear sonar, two to four ultrasonic sensors are mounted on the rear bumper to detect an obstacle
from 2 to 2.5 m away. The main characteristics of ultrasonic sensors for rear sonar are directivity, ringing
time, sensitivity and sound pressure. Directivity of an ultrasonic sensor corresponds to the size and shape
of the vibrating surface (that is emitting the ultrasound) and the frequency at which it vibrates.
Consider the MA58MF14-7N device as an example sensor. This device has notches to identify the
directivity of the sensor. As Figure 4 shows, the MA58MF14-7N device has a wider view in the horizontal
direction than in the vertical direction which means it is an “Asymmetric” ultrasonic sensor. We will be
using “Horizontal” placement, which can provide wider coverage with fewer sensors, while narrower
vertical directivity improves sensor usability by limiting the effect of reflection from the ground.
4.2 Sensor Circuit Implementation
The transformer-driven configuration uses a center-tap transformer to boost the DC VPWR voltage to a
high-voltage sinusoidal driving signal at the secondary. The transformer installed on the daughter card is a
fixed-type EPCOS B78416A2232A003. The transformer-driven configuration is typically reserved for
closed-top transducers, which require higher driving voltages than open-top transducers. For this reason,
the closed-top 58.5-kHz Murata MA58MF14-7N is paired with the transformer. As can be seen in the
schematic above (which image?). As Figure 3 shows, overall there are very few components on the
sensor PCB and the major space-consuming components are the transformer, 100-µF capacitor (C11),
and the PG460-Q1 device.
For automotive applications, the Iso pole is a 75-mm diameter pole which needs to be detected within the
entire range from minimum to maximum distance. In this section, register settings and associated device
response are illustrated which can be used as a starting point for device configuration. These settings can
be further optimized based on algorithm and range requirements.
The PGA460-Q1 EVM GUI was used to optimize the device parameters. There are two threshold sets –
Preset 1 (P1) and Preset 2 (P2). P1 is optimized to detect objects in the range of 20 cm to 50 cm with less
number of pulses, lower current and shorter record time. P2 is optimized to detect objects in the range of
40 cm to 2.7 m, with a larger number of pulses, higher current, and a longer record time. With the settings
shown in Figure 5, the sensor was able to detect an ISO pole in the range as shown in Figure 4.

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Figure 4. Iso Pole Range

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Figure 5 shows a screen shot of the general device settings.
Figure 5. General Device Settings

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Figure 6 shows the time-varying gain settings.
Figure 6. Time-Varying Gain Settings

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Figure 7 and Figure 8 show Preset 1 and Preset 2 threshold settings.
Figure 7. Preset 1 Threshold Settings

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Figure 8. Preset 2 Threshold Settings
Figure 9 illustrates the data monitor screen, demonstrating detection of an object as close as 20 cm from
the sensor.
Figure 9. Data Monitor