Cascading WS2803 LED drivers, each with different output current
WS2803 provides nearly no variations in current from channel to channel  


Means that the adjacent LED channels will sink nearly the same amount of current (+/- 2%) when they are set to the same duty cycle.  


  and from IC to IC  


Refers to the promise that separate chips are guaranteed to drive the leds at nearly the same current (within +/- 4%) when sharing identical current setting resistors.

So you can configure the current separately for each chip, although not for each channel within a chip. The drive current is determined by the resistance of the current setting resistor Rext, which should be connected between the Iref pin and ground:



Where Vrext is equal to 1.25 V.
To drive the outputs of a WS2803 at 15 mA, you need a resistance of 22 * 1.25 V / 15 mA = 1833 Ω, while for 20 mA you need 22 * 1.25 V / 20 mA = 1375 Ω.  

While the drive current of adjacent channels is fixed, the LED brightness can still be controlled on a per-channel basis with pulse width modulation: The leds are rapidly switched on and off at 4687 Hz, and they can be set individually to 256 different values between off all the time (0) and on all the time (255).