In-depth analysis of T-box system solutions: emergency call unit

alan000345 · Published on 2018-10-17 09:17

In-depth analysis of T-box system solutions: emergency call unit [Copy link]

Section 4 Emergency Call Unit eCall (Emergency Call) is a 102)]T-BOX is an important part of the car. When an accident occurs during driving, eCall establishes contact with the rescue center through mobile phone and satellite positioning function and mobilizes rescue services in time, thus saving lives.

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Figure - 1

“Safety is no small matter; life is more important than anything else. "The EU has clearly stipulated that all cars sold after April 2018 must be equipped with the eCall in-vehicle system. The draft draft prepared by the United Nations also made clear requirements on call duration, backup battery and sound intensity. The call (Voice Communication Mode) duration is not less than 5 minutes, and the call callback (Callback Mode) duration is not less than 20 minutes; the backup battery can only power the in-vehicle system IVS (In-vehicle System); the receiving loudness level RLR (Receiving Loudness Rating) is 2dB. I believe that in the future, China will further formulate unified standards and mandatory standard configurations.

For eCall, TI provides the following system solutions and reference designs:

TIDA-00159 uses a wireless modem (Sierra Wireless Modem) to convert between analog and digital signals, while TIDA-00724 uses an audio codec (TI CODEC).

System Introduction

The following takes the TI reference design TIDA-00724 as an example to introduce the eCall system.

eCallThe system block diagram is shown in Figure 2. When an accident occurs, the audio signal is amplified by the audio amplifier (Audio AMP) to the input range that the ADC can recognize, and the analog signal is converted into a digital signal; the digital signal is connected to the call center through wireless connection (Wireless Connectivity), and the vehicle location is quickly locked through GPS, and the relevant response signal is returned; the response signal is converted into an analog signal by the DAC, and then further amplified by the Class-D power amplifier (Class-D AMP), thereby driving the speaker to sound.

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Picture- 2

1) Audio Amplifier (Audio AMP)

When the analog signal passing through the microphone is small, it needs to be further amplified by the audio amplifier before being used as the input of the ADC. TI's recommended OPA1662-Q1 is a dual bipolar input operational amplifier that provides low noise density and ultra-low distortion of 0.00006% (1kHz), which can maximize signal output. 2) Audio Codec (CODEC) The audio codec in the eCall system must be able to support full-duplex communication between the digital audio source from the wireless module, the microphone input, and the speaker output. The models recommended by TI are TLV320AIC3104-Q1, TLV320AIC3106-Q1 and TLV320AIC3106-Q1. 102)]TLV320AIC3109-Q1, their main differences lie in the number of ADC/DAC channels and the number of audio input and output channels.

[tr ][td=160]ADC signal-to-noise ratio (dB)DAC signal-to-noise ratio (dB) 102 Analog input channels [td=160]6

	TLV320AIC3104-Q1	TLV320AIC3106-Q1	TLV320AIC3109-Q1
ADC channel	2	2	1
92
DAC channel	2	2	1
10	4
Analog output channels[/td][ td=160]6	7	6
Maximum sampling rate (kHz)[/td ][td=3,1,479]96
Digital audio interface support	L, R, I2S, DSP, TDM

[ size=14px]Usually use TLV320AIC3104-Q1, which is a dual-channel audio codec that meets low power requirements and has [color=rgb(170, 102, TI also provides the input and output required for eCall applications. Corresponding evaluation board: TLV320AIC3104 Evaluation Module. The features of this chip are listed as follows:

Optimize the performance of voice applications;
Support high-definition voice/wideband audio;
Flexible interface , supports multiplexing;
effectively suppresses noise and increases dynamic range. The additional differential outputs of the audio codec require protection from ESD. The ESD protection device recommended by TI is TPD2E007 can still provide protection at 8kV contact discharge and 15kV air discharge. Its breakdown voltage is 14V, much higher than TLV320AIC3104-Q1 Working voltage range.
3) Class-D AMP 85)]The power amplifier options are Class AB or Class D. Class AB is a linear amplifier that does not generate electromagnetic interference (EMI) and does not require many external electronic components. However, The efficiency is very low, and a lot of heat dissipation measures are required. Class D amplifiers are efficient switching amplifiers and do not require too many heat dissipation measures. Although Class D amplifiers require output inductors and cannot avoid the impact of EMI, TI uses BD mode modulation to reduce The ripple current of the inductor. Since the price of backup batteries is very expensive, if a class AB amplifier is used, most of the energy will be lost in the form of heat, so it is more cost-effective to use a class D amplifier. /color]
Applied to eCallClass D amplifiers in situations also need diagnostic and Protection function. Load diagnosis before a collision helps to feedback any problems with the system to the driver for maintenance; if a fault occurs after a collision, the call center can be directly notified of the speaker failure. Although in eCall is unlikely to be damaged by high voltage, but the connection Speakers and [url=http://www.ti.com.The eCall cable is likely to be shorted to the power supply or ground during installation, maintenance and failure. Even a momentary event may cause damage to the Class D amplifier, so integrated protection circuits are also required for these events, reducing the need for external devices and reporting problems through I2C. TI's main recommended devices include TAS5411-Q1, [ url=http://www.ti.com.cn/product/cn/TAS5421-Q1?keyMatch=TAS5421-Q1&tisearch=Search-CN-Everything]TAS5421-Q1[/url]andTPA3111D1-Q1. For most applications requiring disconnection and integrated protection, the 8W TAS5411-Q1 is the preferred choice. For higher power consumption requirements, the 22W TAS5421-Q1 is recommended (except for power, the other configurations are the same as the TAS5411-Q1). For low-end applications that do not require integrated load diagnostics or protection, the TPA3111D1-Q1 is a good choice. The features of the TAS5411-Q1 recommended by TI are listed as follows: