cooldown is the time between shots.
to fire three in a row from a single spot you'll most likely have to use three launchers.
or, you can put 3 charges in a tube, with say, 0.2 cooldown time, 0.5 recharge and 2.99 as minimum fire charge.
if you want to have fixed amount of charges, you'll need three launchers. each one with the cooldown time as long as you want the "recharge" time to be, with no recharge time and with as much as max shots as you want, divided by the amount of tubes.
remember that also the phaser strenght affects pulse load and fire rate, if you use MLeo's detail/nit fix.