What I want to know is, am I doing this correctly? Are my calcualtions right? Will the chip be able to handle outputting 3x as many milliamps if I cut the voltage by a third?
What I want to know is, am I doing this correctly?
Keep in mind that 110ma limit only applies if you have all 8 outputs on continuously. If you are driving different numbers of outputs at any given instance or is you decrease the duty cycle by saying driving the inputs with PWM signals at different duty cycles you can push that spec higher as the duty cycle graphs show in the data sheet.
The limit is 350mA per output at 100% duty, the absolute maximum rating 500mA.
500 mA output source current capabilityRecommended for high-side switching applications that benefitfrom separate logic and load grounds, these devices encompassload supply voltages to 50 V and output currents to -500 mA.Output Current IOUT -500 mAOutput Source Current (Outputs Open) lOUT VIN = 2.4 V, VCE = 2.0 V 2 -350 mAAllowable peak collector current as a function of duty cycle
The suffix "A" indicates an 18-lead plastic dual in-line packagewith copper lead frame for optimum power dissipation. Undernormal operating conditions, these devices will sustain 120 mAcontinuously for each of the eight outputs at an ambienttemperature of +50°C and a supply of 15 V.
It says 140mA on a 1/10 duty cycle, but it also says that the pulses have to be less than 0.1ms which is 100 nanoseconds.
chip would have to be able to source at least 300mA
Keep in mind... those are extreme test conditions and supplied as a reference... not a "requirement"
Do some tests... with those limits in mind.
Though... my opinion is that 1/8th duty cycle is just gonna be DIM unless it's REAL FAST.
0.1ms which is 100 nanoseconds
So I think I'll have +9v on the source ic input
Not in this part of the galaxy, it isn't.
Maybe you will, maybe you won't: the odds are pretty good that your 9V supply is unregulated. You need to make sure that the supply feeding your LED drivers is regulated, because relatively small changes in LED voltage can make destructive differences in current.
And don't forget that whatever you use for a sink driver will have a voltage drop across it, just as the source driver does.