Here’s a quick reasonableness check for 3 A at 5 V using LM2678SD-5.0/NOPB and a 100uH Inductor, assuming the LM2678’s fixed fSW from the datasheet.
Datasheet facts (LM2678)
Fixed switching frequency: 260 kHz typical (225–280 kHz over temp).
Capable of driving up to 5 A loads.
Inductor selection guidance targets about 30% ripple of IOUT(max).
Source: TI LM2678 datasheet.
Ripple with L = 100 µH, Vout = 5 V, Iout = 3 A
At Vin = 30 V:
ΔIL = 0.1603 A pk–pk
Ripple = 5.34% of 3 A
Inductor peak current = 3.080 A
Recommended Isat (≥1.2 × Ipeak, per best practice) ≈ 3.70 A
At Vin = 10 V:
ΔIL = 0.0962 A pk–pk
Ripple = 3.21% of 3 A
Interpretation
LM2678-5.0: Suitable for 3 A (datasheet up to 5 A).
100 µH inductor: Electrically “safe” with very low ripple (3–5%), but this is well below the datasheet’s ~30% ripple design target. That usually means:
Slower transient response and physically larger inductor.
Ensure Isat ≥ 3.70 A and check DCR for I²R loss and thermal rise.
If you want closer to the datasheet’s ripple target (20–40% rule-of-thumb), a smaller L is typically used. With 100 µH you’ll have low ripple and gentle dynamics; acceptable if the choke meets Isat/DCR and transient response is okay for your load.
If you’d like, I can propose concrete inductor options (Isat ≥ 3.7 A, low DCR) and verify output-cap ESR per the LM2678 stability guidance.