With the growing popularity of modern car sales, the automotive industry has seen significant improvements in its process development. However, the demands placed on automotive power supply systems have become increasingly complex. It is well known that a specialized voltage regulator is an essential component within a vehicle's power system. As automobile manufacturing processes continue to evolve, there is now a higher standard for the performance of buck regulators used in these systems.
This article explores Linear Technology’s LTC7138, a step-down regulator designed specifically for automotive environments. The LTC7138 is a 400mA buck converter capable of operating from an input voltage range of 4V to 140V, making it ideal for applications that experience severe voltage transients, such as industrial, telecommunications, and automotive systems. Its hysteresis architecture eliminates the need for external compensation, simplifying the design process. The output voltage can be set to 1.8V, 3.3V, or 5.0V via dedicated pins, or adjusted between 0.8V and VIN using an external resistor divider. Additionally, the internal P-channel FET allows for 100% duty cycle operation, enhancing efficiency in low-voltage scenarios. The LTC7138 is housed in a thermally enhanced high-voltage MSOP package, ensuring reliable performance in demanding conditions.
One application example involves a simple 5V/400mA step-down converter with a wide input range. As shown in Figure 1, this circuit uses only four external components and sets the output to 5V by connecting the VPRG1 pin to the SS pin and VPRG2 to ground. No external compensation is required, making it a compact and efficient solution.
Figure 2 illustrates the efficiency of the 5V regulator, which maintains high efficiency across a wide load range thanks to Burst Mode operation and a low 12μA quiescent current. At a 12V input, the efficiency peaks at 87% for a 10mA load and remains above 80% even at 0.4mA, making it suitable for always-on battery-powered systems.
Another configuration involves two LTC7138s connected in parallel to deliver 24V/800mA. As depicted in Figure 3, the master device controls the slave through the FBO and VFB pins, ensuring synchronized burst mode operation. With a 48V input, the full-load efficiency reaches an impressive 93.6%, as shown in Figure 5.
The LTC7138 also serves as a surge suppressor, capable of handling inputs up to 32V. When the input exceeds this threshold, the regulator switches to maintain regulation, as illustrated in Figure 7. Additional overvoltage protection can be achieved by connecting the OVLO pin to a voltage divider. This makes the LTC7138 ideal for protecting downstream components in automotive, industrial, and avionics systems.
Other notable features include a RUN pin for external UVLO, an ILIM pin for current limit programming, and a soft start function (either internal or external). These features enhance flexibility and reliability in various applications.
In summary, the LTC7138 offers a robust and efficient solution for automotive power systems. With its wide input range, low component count, and advanced features, it is well-suited for a variety of challenging environments. Whether used as a simple buck converter, a high-current parallel system, or a surge protector, the LTC7138 demonstrates the evolving capabilities of modern automotive power management.
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