1kHtz?

Ahh, well what you'd want to do with setInterval is something like this:

setInterval(function() {
  digitalWrite(pin,1);
  setTimeout(function() {
    digitalWrite(pin,0);
  }, 2); // 2ms @ 100Hz = 20%
}, 10); // 100 Hz

(So you use a setInterval for each full cycle, and then setTimeout for each pulse)

Or you could use the built-in digitalPulse:

setInterval(function() {
  digitalPulse(pin,1,2); // 2ms @ 100Hz = 20%
}, 10); // 100 Hz

Hopefully those should work on anything