AL1676-30A LED Driver output current rating
The short answer is both specs are valid but your experience in reading and comprehending datasheets is weak.  The Peak current is often > 10x the average current spec for switch efficiency reasons and small package thermal rise.  
  
  Duty Cycle, d (or Duty Factor) also plays a part in this ratio of Imax/Idc (for recommended &lt;300mA rating.)


 sage advice

for all questions on MOSFET current ratings used as switched current devices.


Keep this pk/avg ratio in mind when choosing MOSFETs and % losses in future.  Also understand DC Motor Current starts with the ΔV/DCR=Istart ratio then reduces to 10% of this at full load at max Hp ( usually 80~90% max RPM). Also all capacitors including batteries have ESR which limits the pulse current to ΔV/ESR= ΔI. Thus  peak currents for charging batteries or bridge caps can be much higher than average and driver RdsOn must be computed in charger losses thus that Pd * d/ESR=I² using duty cycle, d.  This is simply  Ohm's law, time averaged and re-arranged.


The first page and 1st line under Features on the datasheet says >90% Efficiency. You cannot achieve this unless your losses proportional to total loop current R (incl load) are &lt;10% which means the RMS current must be &lt;10% of the Imax and thus must be >10x to achieve the recommended Idc &lt;300mA used and >90% efficiency.

Details

When you understand the use of Ohm's Law for power dissipation, efficiency , thermal resistance, heat sink design and temperature rise. It will all become clear. It is assumed you understand the following equations from Ohms Law and Thermodynamics.


\$P_D=I^2R_{DS(ON)}*d\$    .......(1)


for duty cycle d {0~1) and then junction temp rise 

\$\Delta T_{JA}=P_D*(θ_{JC}+θ_{CA}) \text{ or } = Pd*(Rjc+Rca)\$  .........(2)


with no heatsink except 2"x 2" (or 26 cm  and free air convection THERMAL RESISTANCE is defined as (depending on font format limits of text);
Datasheet specs are ALWAYS given with an infinite heatsink @ Tj=25'C but  tested with a thermal junction thermal base regulator in a pulse mode (unless otherwise specified) 



basil advice

(small pun)


Designers must understand this to DERATE the PD limits according to their Ohm's Law application of thermal resistance and limited thermodynamic understandings of heat velocity (slew rate °C/s), steady Thermal resistance °C/W and resulting junction rise, °C or °K ( same for ΔT)


\$Rja \text{ or } R_{JA} \text{ or } \theta_{JA}=123°C/W\$  for SO-7 case


There are thermal limitations of instantaneous junction temperature rise and the  peak current safely not given for Pd and this is what defines the part number and its corresponding current limit.  e.g. AL1676-xxAS7-13 where xx means the Max x.x Amp peak limit for p.n.'s with xx= 10,20,30,40  \$ I_{DS} \$ and corresponds to the Max \$R_{DS(ON)} \$ of 12Ω, 6.5, 3, 2.5.  Also note the xx is followed by a Letter A,B,C or D which must denote internal  resistance (either electrical or thermal) for minimizing junction temp rise or fusing current margin of wirebonds.


Validation on assumptions


Using equation ...(2), for example, part number ratings, with Rca=0, and Rjc=19 °C/W (from spec Note 5, 1"x1" FR-4  2oz Cu with min. footprint), we get:


for 4A rated part Pd=(Ids)²•RdsOn = (4.0A)²•2.5Ω = 40 W
since we know Diodes Inc has a OTP shutdown at 150°C and from Rja we would expect it happen very fast or else you would use Ids (Max) with a duty cycle well below 20% or you have an excellent CPU style heatsink with Rca=0.2°C  



Using the data in the datasheet there must be some sorting or process  differences to separate each final part number.  I suspect they are all made with same design but process controls and variations together with 100% testing with ICT test results will determine final part number.

AL1676-20AS7-13 = AL1676-xxyS7-13 with bins for xx and y.   

p.n.               RdsOn    Ids Vds(max)    Pds     category
                    [Ω]     [A] =Rds*Ids    Max [W]  from p.n.
 AL1676-20AS7-13    6.5 Ω   2 A     13 V    26 W    A
 AL1676-30AS7-13    3.0 Ω   3 A      9 V    27 W    A
 AL1676-10BS7-13    12.0 Ω  1 A     12 V    12 W    B
 AL1676-20BS7-13    6.0 Ω   2 A     12 V    24 W    B
 AL1676-20CS7-13    5.5 Ω   2 A     11 V    22 W    C
 AL1676-40DS7-13    2.5 Ω   4 A     10 V    40 W    D