Selection and design method of intelligent high-side switch driving vehicle lamp load

In automotive applications, high-side switches are commonly used in central body control module BCM applications. The main function of Z in BCM is the driving control of the lights. Today, let us introduce the points that need to be paid attention to when driving the lamp load in automotive applications, as well as the selection and design method.

In automotive applications, high-side switches are commonly used in central body control module BCM applications. The main function of Z in BCM is the driving control of the lights. Today, let us introduce the points that need to be paid attention to when driving the lamp load in automotive applications, as well as the selection and design method.

1. Today’s typical automotive lamp Electronic and electrical architecture and future trends

Today’s typical automotive lighting electronic and electrical architecture is the mainstream of the centralized architecture. The front and rear lights are mainly bulb-like loads and are directly driven by the central body control module BCM. Recently, a partially decentralized architecture is becoming a trend. There are both bulb-type loads and LED-type loads in the lamp configuration. The BCM has to drive both the bulb and the LED light module. In the future, the configuration of all-LED front and rear lights is becoming a trend. LED lights have become a symbol of the car’s personality. The BCM will evolve into a controller responsible for coordinating communication with the headlight and taillight LED light modules.

Selection and design method of intelligent high-side switch driving vehicle lamp load

2. Which lights in the vehicle usually need to be driven?

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1) No.
2) 27W in North American Standard
3) 7W in North American Standard
4) Not in North American Standard as a regulatory requirement
5) 65W in North American Standard

In a typical automotive system, the exterior lighting bulbs or LEDs are typically driven by high-side switches. Based on the vehicle regulations of various countries, a car must be equipped with up to 20 lights of 8 types. The list above lists the various lamp load information required by regulations.

Although not mandated by regulation yet, lights based on the list below are often used and driven by high-side switches.

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1) No.
2) 7W in North American Standard
3) 27W in North American Standard
4) Daytime running lights are required by regulations in some countries and can also be implemented by low beams.
3. What products are suitable for driving the light load?

In shrinking body control modules, such as the central body control module (BCM), more and more functions (eg, exterior and interior lighting, relay control and various comfort functions) are being accommodated requiring JQ-designed products. to support a highly integrated product with scalability and flexibility to meet a wide range of needs. Therefore, the intelligent high-side switch is more suitable for driving the light load.

4. The characteristics and driving requirements of the lamp load

The main application of a high-side switch is to turn on a light bulb. At the moment when the power is turned on, especially when the lamp is cold, a very important transient current (Inrush current) will flow into the lamp. For a high-side switch, the effect of this current is similar to a short circuit, so to protect the device, the device may shut down. This limits the bulb drive capability of the high-side switch.

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1) When the supply voltage is 18V
2) When the power supply voltage is 18V and PWM modulation is implemented according to the high brightness regulations
3) When the supply voltage is 18V and PWM modulation with a duty cycle of 2% is implemented

As shown in the table above, the commonly used car light bulb load characteristics and inrush current are determined by IDC, IINRUSH and tLAMP_ON. Three parameters describe the working state of the bulb. IDC defines the current consumption at steady state, IINRUSH peak current, while the time constant tLAMP_ON describes the transition time to reach steady state. It is generally believed that IINRUSH is 10 times that of IDC. When the driving current is reduced to less than half of IINRUSH, the lights are fully turned on. This time is defined as tLAMP_ON. If the high-side switch has short-circuit protection and turn-on retry due to inrush current, then tLAMP_ON is defined as the time required for YC turn-on retry from start to Z later. tLAMP_ON should be ensured in the lamp design
A good smart high-side switch is necessary to meet such a light-driving challenge.

5. What characteristics does a good smart high-side switch need to have?

In order to cope with the cold-state inrush current of the automotive light bulbs mentioned above, a good smart high-side switch needs to have sufficient short-circuit tolerance.

Smart high-side switches with short-circuit protection limit current in the event of a short-circuit. Under Z-worst conditions, when inrush current flows through the bulb, the current limit of the device is reached. When the device current limit is reached, the junction temperature rises and the lamp is turned off to limit thermal stress. Because PROFET devices are retryable product types, the bulb will still be turned on. As shown above, typical applications AL for device restart due to current and relative constraints. If the current limit IL5(SC) is reached before the filament is heated to a temperature that allows the bulb to fully turn on, the device acts as a short circuit and triggers a shutdown. In this case, the PROFET turns on a 3x21W load. It can be seen that the same current value occurs in DY retries, which indicates that the device current limit is valid. Due to the low ambient temperature, the retries are subject to the dynamic temperature limiter. The lower current on the two retries after Z indicates that the inrush current has flowed, but the thermal inertia of the silicon creates an overtemperature, which triggers the device to shut down and restart after cooling down.

6. Typical solutions and recommended product combinations for BCM applications

The central body control module BCM generally requires a variety of highly integrated products, which can provide various functions in one device. Examples include smart high-side switch PROFETs, multi-channel switches in the highly integrated SPI high-side switch SPOC and SPIDER families, and system basis chips SBCs that provide more functionality in a smaller space. With the multi-HX microprocessor AURIX, you can even integrate two applications in one device: BCM central body control module and gateway. Benefits include enhanced communications, lower power consumption, and select DJ security features.

Its system advantages include:

• Saves board space with integrated features
• Protected load control and sophisticated diagnostic features
• Supports the “Limp Home” functional safety concept
• High scalability and short-circuit tolerance of power semiconductors (PROFET and SPOC)
• Supports smooth transition to interior and exterior lighting bulbs and LED loads.

In summary, we briefly introduce the selection and design method of how to use the intelligent high-side switch to drive the light load. I hope the above introduction can help you to understand related products and their use.

The Links:   EP4CE30F23I7N LM170E03-TLJ5 MITSUBISHI-IGBT

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