Due to harsh automotive environment, car electronics components have to withstand higher voltages, larger transient loads, higher temperatures and higher ESD than commercial or industrial applications.
The input supply from the car battery can experience voltage dips and peaks during cranking or load dump events. And nearby AM receivers are sensitive to switching noise, so switching converter EMI noise must be minimized. The operating temperature range of the application can be much wider than normal commercial applications. Automotive applications require high reliability and good safety protections. Richtek has released new powerful DC/DC step-down converters and design tools that simplify the automotive power design considerably. In general the various RT2875 versions offer an input voltage range of 4.5 - 36V with outputs voltages of 0.6 – 24V at currents of up to 3A. The programmable current limit ranging from 1.5-6A allows to cope with all kinds of overloading especially coming from inductor peaks. There are three parts in the RT2875 family :
- RT2875AQGCP with 2% reference voltage accuracy and latch-off UVP protection
- RT2875BQGCP with 2% reference voltage accuracy and hiccup UVP protection
- RT2875DQGCP with 1% reference voltage accuracy and hiccup UVP protection
Whether to choose Latch-off or hiccup mode protection depends on user preference. Latch-off UVP protection always needs system intervention to reset the converter (via enable pin) after an output undervoltage condition has been triggered. Hiccup mode UVP protection devices will automatically try to recover from output under-voltage condition. The hiccup mode will ensure low power consumption in continuous overload. In most applications, hiccup mode is the preferred protection mode. If very high output accuracy is needed, RT2875D may be the best choice, but for most applications 2% reference accuracy (over the full temperature range) will be sufficient.
The designing of an automotive application with RT2875 takes some extra effort if all aspects of automotive environment need to be taken into account: Component tolerances and parameter drift over temperature need to be considered to ensure correct operation over all critical conditions. The Richtek Designer simulation tool can be used as a good guideline to calculate initial component values, and can be used to estimate performance over component value changes. The feature set of RT2875 meets the requirements of several automotive applications, and performs well over a wide range of input conditions and switching frequencies.
Key Features for RT2875:
- AEC-Q100 Grade-2 qualified over -40 ~ +105°C temperature range.
- The wide 4.5V ~ 36V input voltage range & 100% duty-cycle mode minimizes output voltage variation over input voltage fluctuation.
- Programmable 300kHz ~ 2.1MHz clock which can be synchronized to an external clock for precise frequency setting to avoid sensitive frequency bands.
- Programmable 1.5~6A current limit sets the maximum inductor peak current to a specific value, allowing optimal inductor choice without risk of saturation in overload condition.
- External compensation to set feedback loop parameters and ensure stable operation at various switching frequencies over the full temperature range.
- Low RDSON MOSFETs and a thermally efficient package allow operation at high ambient temperatures without overheating.