What this dual pre-biased transistor does in an automotive ECU
The RN4985FE,LXHF(CT packs one NPN and one PNP pre-biased transistor into a single SOT-563 package, with integrated bias resistors R1 at 2.2 kΩ and R2 at 47 kΩ. This eliminates two external resistor pairs per channel, saving board space and reducing pick-and-place cost on automotive ECU boards where every mm² counts. The 50 V collector-emitter breakdown and 100 mA continuous collector current handle typical 12 V and 24 V automotive loads — solenoid pre-drive, relay coil kickback clamping, or logic-level translation between a 3.3 V MCU and a 12 V bus.
This part carries AEC-Q101 qualification, which means it has passed the automotive stress tests — high-temperature reverse bias, temperature cycling, autoclave, and pre-conditioning — that consumer-grade transistors skip. For a Tier-1 supplier's PPAP submission, the AEC-Q101 cert is a line-item check. The series is listed as Automotive, AEC-Q101, and the product status is Active, so there is no LTB clock ticking.
Sourcing this for a production BOM
If you are qualifying a second source for a long-run automotive program, the RN4985FE's pinout and resistor values should be matched against any pin-compatible dual pre-biased transistor in the same SOT-563 footprint; the 2.2 kΩ base resistor and 47 kΩ emitter-base resistor are the values that define the switching threshold, not just the package outline.