tlc5940 PWM Question

Hi,

My project on the TLC5940 using arduino duemilanove gets the output.
I am using entirely TLC5940 library from

http://code.google.com/p/tlc5940arduino/

My first code was just simple full on/off each second. They seem to be working until I checked on the PWM waveform on oscilloscope.
When I set the LED fully off, the duty cycle from TLC5940 is indeed very close to 100% (that not exactly 100% was not a problem to me)

But when the LED if fully ON, the duty cycle is only 60%(I was expecting it to be almost 0%, or at least less than 10%)

Just for clarification, TLC5940 uses current sinking method to turn led on. Higher duty cycle means dimmer light and so on.

From what I observed, when I set the brightness to 4095(max) the duty cycle is just like this:

I am using a 5V to power the LED. All 16 Channels on/off at the same time. So the PWM is the same.

If anyone can tell me what is the problem here? Or this is just normal? Please. Thank you.

Anyone knows?
Don't want to sound to desperate but this is really out of my head