Why so large difference
I understand from the datasheets of the chip and the Kingbright display that the IC's supply voltage has to be exactly 10volt (regulated).
Supply voltage (VDD - VSS).......................... +4.75V to +11V
And that the LED current (brighness) is 20x the current into pin 19.
And that that current has to come from the 10volt supply.
I would try an opto coupler.Opto LED driven via 1k current limiting resistor from a PWM pin.Opto transistor and a 100k trimpot in series between pin 19 and 20 of the LED driver.Set the trimpot to max LED current (20mA).
A simple yes or no is not going to help OP.