In-depth analysis of T-BOX system solution: power rail

The Telematics Control Unit (TCU or T-BOX) is an embedded vehicle system that can be used in the fields of wireless tracking and communication of vehicles. The system can be divided into modules such as power rail, charging management, interface, emergency call unit, wireless connection unit, antenna, etc. The system is divided as follows:

The first section begins with an introduction to the power rails.

The T-BOX power module can be divided into two parts: power rail and charging management. The power rail mainly analyzes the primary power supply and secondary power supply of the T-BOX and estimates the overall power situation; while charging management is mainly for the backup battery. The following figure shows the relationship between VBAT, backup battery, power management and load. Under normal circumstances, VBAT will charge the battery while supplying power to the load; when encountering an emergency (such as a car crash), VBAT fails, and the backup battery will supply power to the load.

1) Primary power supply

There are currently three mainstream solutions, namely, reducing voltage only, boosting and reducing voltage, and reducing voltage first and then boosting voltage.

Option 1: Only reduce blood pressure

This solution is relatively simple. VBAT enters the secondary power supply after passing through a wide input range buck (Wide Vin Buck) or a wide input range linear power supply (Wide Vin LDO).

When in low power consumption (such as sleep mode), the system will disconnect the Wide Vin Buck (LMR33630-Q1 or LMS3655-Q1) and power the MCU separately through the low quiescent current Wide Vin LDO (TPS7B69-Q1) to reduce power consumption. The current sensor monitors the current to prevent overcurrent. In addition, there is reverse battery protection.

Option 2: Both boost and buck

Compared with Solution 1, Solution 2 adds pre-boost. There are two reasons why Pre Boost (TPS61088-Q1) is needed: First, the output voltage of the primary power supply is greater than 5V. Under normal circumstances, the operating voltage of VBAT is 12V (automotive level), but under special circumstances (such as ignition), the output voltage of VBAT may be less than 5V. At this time, the primary power supply can only use Boost to ensure that the output voltage is greater than 5V; second, the load has special requirements, such as the Class D power amplifier used in E-Call, whose power supply voltage is generally above 9V, and pre-boost (Pre Boost) is also required to supply power separately.

Option 3: Lower the voltage first and then increase it

This solution is also used when the load has special requirements (such as a higher supply voltage), but it is relatively rare because of its low efficiency.

2) Secondary power supply

Generally speaking, the secondary power supply directly supplies power to the load. Loads that are very sensitive to noise and have a small output current can be powered by a linear power supply, such as the audio decoder (CODEC) in E-Call; while loads that are not sensitive to noise and have a large output current and a large voltage difference should be powered by a switching power supply. T-BOX involves many types of loads, and the following takes Solution 2 as an example to introduce them in detail.

Microprocessor (MCU) --- Since the MCU has the function of monitoring whether other modules are working properly, it is best to power it separately. Buck or LDO can be used. Here, the buck chip TPS62160-Q1 can be selected.

Audio decoder (DODEC) is an important device in E-Call. Audio decoder generally requires two power supplies, 3.3V and 1.8V. For 3.3V, you can choose TPS7B6933-Q1, whose input voltage range is 4-40V; for 1.8V, you can choose TPS76918-Q1, which has low quiescent current, low price and small package.

Processor (4G Processor)---The operating voltage is 3.8V, and the buck chip TLV62065-Q1 can be selected, and its output current can reach 500mA.

Antenna (4G Antenna)---The signal is at the RF level and has high requirements for EMI. TI has a dedicated Antenna LDO, such as TPS7B7701-Q1.

Wireless Connectivity --- This part includes GPS, WIFI, BLE, etc. The power supply voltage of GPS and WIFI is 5V, which requires a large current and can be directly powered by a primary power supply (LMR33630-Q1 or LMS3655-Q1); the power supply voltage of BLE is 3.3V, and TPS7B6933-Q1 can be selected.

Audio Amplifier (Audio Amp)---It is also an important device in E-Call. TPS61088-Q1 can be selected.