要約

Automotive infotainment, cluster head unit, and telematics require dedicated front-end voltage regulators that withstand load dump, start-stop, and battery cold crank. The use of dedicated voltage regulators reduces purchasing power due to low volumes, results in longer design cycles, and longer time to market. In response to these challenges, a flexible frontend PWM controller configurable as boost or SEPIC or flyback converter has clear advantages of economies of scale and ease of reuse.

Introduction

Modern cars require dozens of electronic control units (ECUs), each taking power from the car battery with the intermediation of an on-board frontend voltage regulator. Typical application examples are the cluster and infotainment head units (Figure 1), car radio, and telematics.

The frontend voltage regulator must meet many challenges inherent to the automotive environment, like high efficiency, small size, battery load dump, cold crank, and EMI.

This design solution introduces a flexible controller IC that supports many architectures and greatly simplifies automotive frontend voltage regulators design. This innovative boost/SEPIC/Flyback controller IC solves the technical challenges with small PCB footprint, high purchasing volumes, and short cycle times.

Typical Automotive System

Figure 2 illustrates a high level automotive system including infotainment, cluster, audio, and telematics.

Automotive infotainment head units combine entertainment, multimedia, navigation, and driver information into one module. Their power sources are usually attached directly to the main battery through a robust pre-boost front-end voltage regulator (Figure 2 and Figure 3) able to handle variable input voltages and reliably stand cold crank and load dump events through the life of the vehicle. They must also have high switching frequencies to minimize the solution size and to minimize electro-magnetic interference (EMI).

The car electronic instrument cluster digital display reports speed, time, temperature, and other useful information. As for the infotainment section, its electronics are powered by a robust front end boost voltage regulator.

Automotive telematics, a must in modern commercial vehicles, tracks telemetry data including location, speed, vehicle faults and driving behavior. The criticality of this function demands a power solution with input-to-output isolation for enhanced fault tolerance, obtained with a SEPIC configuration (Figure 2 and Figure 4).

Finally, as car entertainment becomes more sophisticated, the audio power budget is being pushed to the limit. The response to the power crunch is the use of high efficiency Class-D amplifiers requiring relatively high input voltages provided by a highly efficient frontend boost converter (Figure 2).

Integrated Solution

As an example, The MAX25200 and MAX25201 are a family of high-performance, current-mode PWM controller with 1.5µA (typ) shutdown current for boost converters with a wide input voltage range. The 4.5V to 36V input operating voltage range makes these devices ideal in automotive applications, such as front-end pre-boost using the MAX25201 (Figure 3) or general-purpose SEPIC (Figure 4) or flyback power supplies using the MAX25200. An internal low-dropout regulator with a 5V output voltage enables the MAX25200 and MAX25201 family to operate directly from an automotive battery input. The input operating range can be extended to as low as 1.8V after startup to ensure reliable operation through cold crank or start-stop conditions. Figure 5 demonstrates the integrity of the output voltage (V_OUT) in presence of a cold crank undervoltage (V_SUP).

The MAX25200's abd NAX25201 fanuky's switching frequency operation (up to 2.2MHz) reduces output ripple, avoids AM band interference, and allows for the use of smaller external components. The switching frequency is resistor adjustable from 220kHz to 2.2MHz. Alternatively, the frequency can be synchronized to an external clock. Figure 6 shows the high-efficiency of the boost controller with various input voltages with a 24V output voltage at 400kHz FPWM.

MAX20200 and MAX25201 family can further improve the system efficiency with the bypass mode operation. For example, if MAX25201 is operated in PWM (SYNC pin pulls high) mode, high-side driver is 100% duty cycle when V_IN > V_OUT, not matter the load. If MAX25201 is operated in SKIP (SYNC pin pulls low) mode, high-side driver is 100% duty cycle only in medium to heavy load (e.g., > 4A) when V_IN > V_OUT.

The programmable Soft-Start feature is also integrated, the boost controller output voltage begins to ramp up using Soft-Start. A spread spectrum option is available to improve system EMI performance. The device features a PGOOD monitor and undervoltage lockout. Protection features include cycle-by-cycle current limit and thermal shutdown. The MAX25200 and MAX25201 family operates over the -40°C to +125°C automotive temperature range and is housed in a thermally enhanced 16-Pin TQFN-EP package.

Conclusion

Modern automobiles are equipped with multiple features, from infotainment to cluster head units and telematics. The fronted voltage regulators must withstand the variability of the battery and adapt to each specific function. We reviewed the challenges related to each function and proposed a flexible, high-performance, current-mode PWM controller configurable as a front-end pre-boost or general-purpose SEPIC or flyback power sup-plies. Its ease of reuse leads to high volumes that increase purchasing power and help reduce the design cycle time by offering a very flexible device.