I have a board with a 16x10 led matrix.
The columns are switched with DMG9933 Dual P mosfets.
The rows are driven with a constant current led driver ST STP16CPC26 (similar to TI TLC5956)
I noticed this problem because there where some ghosting between the columns.
I tried to solve it in software, by adding more blank time. That didn't change anything. The blank time was longer then the on time. Lowering switching speed didn't help either.
I made a diagram of a single LED.
Adding R1 Helped mitigate the problem. R1 needs to be added once per column, not for each LED.
I though at first that it might be leakage current, but this transistor supposed to have that under 10na so i doubt that's the cause. I've built 2 of these boards and both exhibit this problem on all 10 columns. There should be very little capacitance between the LEDs and the drain.
So what is the cause of this? Is this the fault of the led driver maybe?