Under "Recommended Operating Conditions" (page 5) it shows the IN pin can be anywhere from 0V to Vdd where Vdd is the supply voltage you apply to pin 1. You're probably scared off by the "Absolute Maximum Ratings" saying the IN pin is limited to GND-0.3 and VDD+0.3. That just means you can't go lower than -0.3V or higher than VDD+0.3V.
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The Ruggeduino: compatible with Arduino UNO, 24V operation, all I/O's fused and protected