Inductor size is the key to car reversing camera design

I recently talked to some colleagues who designed power for the car reversing camera market. They found that inductor size is an important factor in determining the final design size. For example, the entire camera module measures 20 mm & TImes; 20 mm or smaller. Previously these designs have used LDOs. But with the introduction of higher resolution image sensors and higher frame rate image signal processors, power requirements have increased two or three times, and it is certainly not enough to use LDOs and solve heat dissipation problems in such a small design. With the use of transfer switches, inductors are another component that system designers must consider, so it is important to find the smallest inductor possible.

To address the challenges of space-constrained design, TI developed the LMR22007 device, a 1.6 mm & TImes; 1.6 mm micro-miniature buck converter that requires only four external components to implement a 3.5W design. Therefore, it is well suited for these automotive applications that focus on the solution space (see Figure 1).

Figure 1: 25 mm2 solution size

The LMR22007 has several unique features (such as a default switching frequency of 2.1MHz) that make it easier to design filters that meet EMI standards such as CISPR 25. In addition, the filter components are smaller, further reducing the solution size. 2.1 MHz is not in the AM band (including LW, MW, SW bands). This makes it easier to design smaller filters for the fundamental and its harmonics in the MW band from 535 kHz to 1.8 MHz and the SW band from 5.9 MHz to 6.2 MHz (see Figure 2).

Figure 2. Conducted EMI map with CISPR 25 level 5 limits for the AM band

In addition, LMR22007 has an adjustable current limit option that uses resistor values. This is very beneficial for choosing a smaller inductor when the application requires an output current that is well below the rated 750mA output capability. The control architecture of the LMR22007 is direct control and seamlessly transitions to Power Save Mode (DCS). In the power-saving mode, the switching frequency decreases linearly with the output current, so the efficiency is very stable under a wide range of load currents, as shown in the efficiency graph shown in Figure 3.

Figure 3. Efficiency at load current

I think these features really hit the focus of the car reversing camera design. For a complete power and serial car camera module reference design, download the OmniVision Camera Module (OV10635) system here. Welcome to reply to the blog to share your camera design experience with us.

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