TLC5940 variable current – will this work...

[3dgeo]

Hello,

straight to the questions:

1. Can I connect 3 TLC5940 IREFF pins together without diode like in picture below?
2. Is there any potential issues that can occur while „shorting“ resistors to one of TLC pins to change max current? Goal is to reduce resistance to ground from 4K to 2K, this will change max current from ~10mA to ~20mA.

Current limit will be set only on power on, this design is for a reason...

TLC sets max current according to current flowing from IREF to ground, so I'm assuming my circuit should work, but I need to use 3 times lower resistors than usual due to triple current flow needed for all 3 TLCs, am I rights?

Thanks

[T3sl4co1l]

No, they have to be independent.  The IREF voltage is servoed to 1.24V and small variations between chips will cause one to carry all the current and the others to read ~zero.

If you need to link them together, you need a current mirror, or voltage-to-current converters.

Tim

[David Hess]

A ballast series resistor on each Iref pin could be used in less demanding applications.  This would work better if a reference voltage lower than ground was used.

[3dgeo]

I had a suspicion that small chip variations will cause problems, thank you.
There is no need to link them, it's just there is no space on PCB to put extra resistors, tho looks like I have to find some
If I remove two TLCs from my picture and use 3rd chip output to cut its IREF resistance in half it should be ok? I'll just do same for all chips (I only using 15 outputs on each chip).

[T3sl4co1l]

Yes, that's fine

Tim