Exactly 5V input must give me 30kHz output...
The output is currently connected to a 12bit pulse counter... so as I vary the input voltage I see that the speed of the counter is increasing. However once I hit 3.5V and above the counter stops counting completly as soon as I go below 3.5V it carrys on counting.
I will try to increase my Vsupply to 10V when I get home...because possibly Vin might be limited to Vsupply - 1.5V? This is not mentioned in the datasheet but sounds like a good place to start.