30V high-efficiency DC/DC converter targets automotive applications

30V high-efficiency DC/DC converter targets automotive applications

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By Christoph Hammerschmidt

As fast switching devices, DC/DC converters are a prime potential EMI source. Therefore the R1271 has a Spread-Spectrum Clock Generator (SSCG) for diffused oscillation frequency in PWM operation, which is available as an optional product version. The idea behind using SSCG is to modulate the clock frequency mildly, which results in spreading the EMI energy amongst many frequencies instead of concentrated at one frequency. In this way, the amount of potential interference of the base frequency and its harmonics is reduced considerably.

The device has a series of protection circuits that contributes to the application’s safe operation. The Power-Good pin provides a fault signal to the system when the device is not ready for normal use or when one of the following protection circuits or states is active:

•    CE pin low, chip is disabled

•    UVLO or OVLO protection active, input voltage drops below 3.3 V or rises above 35 V.

•    Thermal Shutdown protection active, chip junction temperature rises above 160ºC

•    Soft-Start time, during start-up or restart

•    UVD & OVD active, output voltage deviates ±10% from nominal setting

•    Hiccup or Latch type overcurrent protection active

The R1271 has a special protection for cranking conditions. A power supply of automotive electronic systems can be subject to a significant input voltage drop when the engine starts. To ensure that the R1271 is able to maintain its output voltage during such event, the clock signal is linearly lowered to one-fourth of its normal frequency. This will make the on-duty larger than the normal maximum duty, which reduces the voltage difference between input and output and provides continuous operation in cold cranking condition. The AEC-Q100 compliance is not yet available, but will be available soon, the vendor says.

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