Texas Instruments PGA460-Q1 Manuale utente

PGA460-Q1

TIDA-01597

Transformer

MA58M

F14-7N

PGA460-Q1

Transformer

MA58M

F14-7N

PGA460-Q1

Transformer

MA58M

F14-7N

TIDA-01597

Local ECU/Main ECU

12 V Load Dump Protected

GND

SN65HVDA100-Q1

OWI Transceiver

MSP430F5529

Launchpad

CC2640F128

TIDUDO4–May 2018

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

Local ECU/Main ECU

12 V Load Dump Protected

GND

SN65HVDA100-Q1

OWI Transceiver

MSP430F5529

Launchpad

CC2640F128

System Description

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2TIDUDO4–May 2018

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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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System Overview

TIDUDO4–May 2018

Automotive Ultrasonic Sensing Module Reference Design for Park Assist

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.

Highlighted Product

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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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System Design Theory

TIDUDO4–May 2018

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.

System Design Theory

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Automotive Ultrasonic Sensing Module Reference Design for Park Assist

Figure 4. Iso Pole Range

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System Design Theory

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Automotive Ultrasonic Sensing Module Reference Design for Park Assist

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

Figure 5. General Device Settings

System Design Theory

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Automotive Ultrasonic Sensing Module Reference Design for Park Assist

Figure 6 shows the time-varying gain settings.

Figure 6. Time-Varying Gain Settings

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System Design Theory

TIDUDO4–May 2018

Automotive Ultrasonic Sensing Module Reference Design for Park Assist

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

Figure 7. Preset 1 Threshold Settings

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Automotive Ultrasonic Sensing Module Reference Design for Park Assist

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

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