300 mA sink current — what it means for relay and solenoid drive
The SN75477DR: The 300 mA per-channel sink rating is the headline load-driving spec. For a typical 5 V relay coil drawing 100–200 mA, one channel has comfortable headroom. Driving two relays simultaneously stays within the package's total dissipation limit, but the 8-SOIC body has limited copper area — if both channels run near 300 mA continuously, a thermal check on the PCB layout is prudent. The driver is a sink-only output (no high-side source), so the load connects between the positive supply and the driver output pin.
It accepts standard TTL or 5 V CMOS logic inputs directly. Do not feed it 3.3 V logic without a level translator — the input thresholds are not guaranteed to recognise a 3.3 V high as a valid logic 1 across the full supply range.
The SOIC-8 footprint is standard and widely supported in assembly houses. No thermal pad — heat dissipation relies on the leadframe and PCB copper.