The most suitable technical requirements for the development of automotive power ICs

1. Requirements for power ICs in the process of automotive electronics

In recent years, the electrification of automobiles has developed rapidly. More and more "high-tech" electronic devices are installed around automobiles, and compared with the era when traditional mechanical control accounted for a large proportion, the proportion of electronic control and electric equipment has become very large. It is expected that the demand for the electrification of automobiles will remain strong in the future.

There are three main reasons for the electrification of automobiles.

The first keyword is "eco". This has played a significant role in the popularization of HV (hybrid electric vehicle) and EV (electric vehicle) to ordinary vehicles. In addition, the competition for low fuel consumption among automobile manufacturers is also becoming increasingly fierce. These breakthroughs are achieved by complex and careful electronic control. Of course, with the popularization of HV and EV and the improvement of fuel consumption performance, the number of electronic devices installed will continue to increase.

The second keyword is "information and comfort". In addition to being a means of transportation, cars are more often seen as daily necessities, and their intelligence is also developing. For example, you can download and enjoy your favorite music, and easily get information about your destination on the road. In order to realize these functions, many communication-related electronic components are required. In addition, the electronicization related to improving comfort is also developing. Smart keys that can open and close car doors and start engines without keys have been basically popularized in ordinary vehicles, making the interior of the car more and more comfortable.

The last keyword is "safety" (satefy), which is indispensable for automobiles. For many years, automobile safety has been achieved through "post-event" countermeasures such as strengthening the rigidity of the frame, cushioning during collisions, and activating airbags for drivers and passengers. However, in recent years, with the improvement of electronic equipment performance, the focus has begun on countermeasures "before" danger occurs. Electronic equipment that achieves automobile driving safety has been established as an important field by improving the accuracy and operation reliability of on-board cameras and on-board sensors, and it is expected that safety equipment with various functions will be developed and put on the market one after another in the future.

Automotive power supply ICs can be used in almost any electronic device. To achieve these three key words, the requirements for performance such as "low quiescent current" (low standby current), "low voltage operation", and "miniaturization and high current" are becoming increasingly higher (Figure 1).

(Figure 1) Electronic background and needs in recent years

ROHM has successfully reduced quiescent current by using its unique circuit design, making a great contribution to the low power consumption of automobiles. For example, ROHM has put into mass production the automotive LDO series "BD7xxL2EFJ-C / BD7xxL5FP-C" that achieves the industry's highest level of 6μA low quiescent current and the DC/DC converter IC "BD99010 EFV-M / BD 99011EFV-M" that achieves 22μA low quiescent current, which is only 1/100 of ROHM's previous products, and has received high praise from customers.

2. Efficiency and its challenges

As I just mentioned, with the popularization of HVs and EVs and the improvement of fuel efficiency, the number of electronic devices installed will continue to increase. This makes the efficiency of electronic components have an increasingly greater impact on improving fuel efficiency.

Among them, the power supply IC is positioned as an electronic component that requires higher efficiency because the consumption current of all electronic components connected to the output end flows through it.

To meet this demand for higher efficiency, pulse control (PWM: Pulse Width Modulation and PFM: Pulse Frequency Modulation) of power supply ICs has become an inevitable trend, but this control method will generate noise interference to surrounding components (Figure 2).

(Figure 2) Types and features of automotive power ICs

Automotive electronic components may malfunction due to noise interference, which may affect human life safety. Therefore, in order for electronic components to work properly at all times, products must comply with various electromagnetic compatibility-related standards such as CISPR25 (interference emission: the standard for the interference-generating side) and ISO11452 (interference immunity: the standard for the interference-affected side).

Therefore, it is very important for automotive products not to interfere with other devices (radiation interference) and to maintain their original performance when interfered by other devices (anti-interference).

EMC (Electromagnetic Compatibility) is called "electromagnetic compatibility" from the perspective of the necessity of having both EMI (emission interference) and EMS (anti-interference).

3. Development of technology and its challenges

The miniaturization of processes once developed rapidly in accordance with Moore's Law, but now there is no longer the significant development trend of the past.

For products such as power supply ICs, power supply ICs with high power consumption also have high power loss. This loss becomes heat and is dissipated from the IC to the outside through the PCB and package (Figure 3).

(Figure 3) Package structure diagram (thermal resistance)

When used in an automotive environment, the ambient temperature is high, and the allowable temperature difference that reaches the upper limit of the IC's operating temperature becomes smaller, so the temperature rise caused by its power loss must be suppressed as much as possible. Therefore, it is necessary to improve (reduce) the heat dissipation performance (thermal resistance) of the chip.

Thermal resistance is not only affected by the material of the package, the material of the lead frame, and the bonding material that fixes the chip to the frame, but is also greatly affected by the frame shape and chip size.

Following Moore's Law, chip size is getting smaller and smaller, which makes thermal resistance higher. Even if the power consumption is the same as before, the temperature rise of the chip will increase.

As the electronic control/electrification of in-vehicle control equipment develops, the commercialization of electronic components is naturally developing under the background of so-called "platformization". Therefore, even if the thermal resistance increases, reducing the chip size is an inevitable choice.

To solve these problems, it is becoming increasingly important to carry out comprehensive heat dissipation design of control equipment and balance the thermal resistance of IC and PCB.

4. Example of automotive EMC countermeasures

As mentioned earlier, automotive electronic components must comply with various electromagnetic compatibility-related standards such as CISPR25 (interference emission: the standard for the interference-generating side) and ISO11452 (interference immunity: the standard for the interference-affected side).

These noise interferences can be divided into conducted noise transmitted directly through wiring and radiated noise transmitted through the air according to the transmission path (Figures 4, 5).

(Figure 4) Noise transmission path on the same PCB

(Figure 5) Noise transmission paths between PCB boards and outside the PCB board

Input filters are very effective as a countermeasure against conducted noise.

The π-type filter is used as the basic type, and a bypass capacitor with lower impedance is connected in parallel for the frequency band that does not meet the standard.

The following application example, the DC/DC converter IC "BD90640EFJ-C", is an example of an application that uses the above noise countermeasures.

In the example of FIG7 , a π-type filter is used to attenuate AM band noise; a bypass capacitor with a resonant frequency of about 20 MHz is used to attenuate CB to FM band noise to meet the requirements of CISPR25-Class5 ( FIG6 ).

(Figure 6) CISPR25 transmission interference limit value

(Figure 7) Example of using an input filter as a countermeasure for conducted noise

However, there is residual noise around 90MHz, so by adding a bypass capacitor with a resonant frequency of around 100MHz, the Class 5 requirement is met in all frequency bands.

Finally, please note that the frequency characteristics of capacitors used as noise countermeasures vary depending on voltage, temperature dependence, size, and component manufacturers, so it is necessary to confirm with the manufacturer before use.

5. Notes on heat dissipation measures

As mentioned earlier, as electronic components become smaller, their heat density becomes higher. Therefore, it is not only more difficult to ensure the normal operation of the supporting equipment as a whole, but also more and more difficult to ensure the life span and reliability.

Thermal design techniques to avoid these problems have become very important factors.

Generally, as long as you know the thermal resistance θJA and power consumption of the IC when mounted on the PCB board, or the thermal performance parameter ΨJT of the center temperature TT of the top of the package, you can know the approximate junction (joint) temperature Tj of the IC. How to control this junction temperature Tj below the absolute maximum rating is the basis of thermal design.

At this point, we must pay attention to the definition of thermal resistance of electronic components. Different manufacturers have different definitions and conditions, which increases the difficulty of thermal design. Although there are JESD51 standard series formulated by JEDEC (Semiconductor Standards Association), due to different understandings of various semiconductor manufacturers, the conditions are not 1 to 1 consistent, which is a common phenomenon. Therefore, attention should be paid to the design stage of supporting products.

Generally, the thermal resistance value defined by semiconductor manufacturers is measured according to JESD51-2A (a PCB board with one IC mounted on it is fixed in a windless space surrounded by a 305mm square cover), which is quite different from the actual usage environment of the supporting products.

For example, the PCB board conditions on the left side of FIG. 8 are the conditions described in the specification sheet of the electronic component.

(Figure 8) Relationship between temperature rise and integration of electronic components

As shown in the middle figure, when multiple components are used in a matching product, placing them in close proximity will reduce the effective heat dissipation area of ​​each component. Note that this means that the temperature of each component will rise due to increased thermal resistance.

Power ICs used in many ECUs in the automotive field are also indispensable products for electronic devices around us. ROHM uses its analog technology to create a rich product lineup of AC/DC converter ICs and DC/DC converter ICs that are suitable for various devices from the primary side to the secondary side. In the future, ROHM will also focus on comprehensive applications that meet the various customer needs mentioned above and further improve its product lineup.