Power tip Designing power supplies for automotive front cameras

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When designing power supplies for front cameras in vehicles, the developer faces four challenges: minimal dimensions of the overall solution, functional safety, cost, and thermal properties. Benefits of designing with multi-channel PMICs.

Gerold Dhanabalan is a Product Marketing Engineer at Texas Instruments in Dallas, USA.

Front cameras are an important component of automotive driver assistance systems and are used, among other things, for pedestrian detection, lane keeping assistants, and traffic sign recognition (Image 1).

Designing power supplies for front cameras presents various challenges, ranging from dimensions and functional safety to low costs and thermal aspects.

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Small dimensions of the overall solution: The installation space behind the windshield is naturally scarce, especially since a camera module may need to accommodate two cameras with different focal lengths. In addition, there is a trend towards higher resolutions and frame rates, while the dimensions continue to shrink.

Figure 2 shows the block diagram of a front camera system that includes not only the actual camera but also an electronic control unit (ECU). The built-in microcontroller (MCU) of the camera module processes the raw image data before it is streamed to the ECU via Camera Serial Interface (CSI)-2. The power supply is provided by a multi-channel Power Management IC (PMIC), which generates the necessary supply voltages for the image sensor and processing functions from a low input voltage.

The image processing processors in front camera applications contain hardware accelerators, for example, for depth and motion detection, while there is a special matrix multiplication accelerator for AI functions.

As a result of this high processing workload, the PMIC should be capable of delivering the necessary currents without excessively increasing the solution dimensions. Its load transient response should be tailored to the changing current demands of the AI processor, with the output capacity being minimal for space reasons. The integration of buck converters, low-dropout regulators, load switches, voltage supervisors, sequencers, watchdog timers, error signaling modules, and other universal inputs and outputs in a single component significantly reduces space requirements compared to a discrete solution.

A two-stage architecture has proven itself. The onboard voltage of 12 V is first converted by a converter, which can handle both voltage spikes up to 36 V and voltage dips down to 3 V, into a regulated intermediate voltage of 5 or 9 V, from which the multi-channel PMICs are finally powered.

Functional Safety: Since the front camera is also used for systems such as emergency brake assistants or adaptive cruise controls, the functional safety aspect is of great importance. The front camera often has to comply with the Automotive Safety Integrity Level (ASIL) B, so the same requirement applies to the PMIC that powers the camera system. Therefore, among other things, voltage supervisors for the various PMIC outputs, a watchdog timer for detecting software errors, and a function for signaling hardware failures are required.

Low Cost: The demand for low costs primarily results from the high production volumes of passenger cars and light trucks. A significant cost reduction is particularly achieved by reducing the number of components, that is, by using highly integrated components based on the appropriate technology. A PMIC saves space and combines multiple power supply components into a single component.

Thermal Properties: The location of the front camera at the windshield means it can be exposed to high temperatures even under normal operating conditions, which can cause increased thermal noise and affect image quality – especially in poor lighting conditions. The small circuit board area and the heat generation within the camera itself further compound the problem. A PMIC with good thermal properties can play a crucial role in keeping the temperature rise on the circuit board within limits. (kr)