So you need to send 2 bytes to the shift register every 20uS? You have 320 clocck cycles to get an update out.
I'm using these:http://www.digikey.com/product-detail/en/IRLML2246TRPBF/IRLML2246TRPBFCT-ND/2639576I think drain current would be 2.4A (24 LEDs @ 100 mA ea), if I'm reading the spec sheet right Figure 13 says Rds(on) for 2.4A would be about 100 m Ohm?
Here's the spec sheet for the LEDs:http://www.us.kingbright.com/images/catalog/SPEC/APT3216SYCK.pdfThe charts don't show anything above 50mA in but by extrapolating I think would be 2.5 - 3 V?
1. Are you using 180 ohm Rext on each TLC5916?2. What 5V power supply are you using? Have you measured its output when all the LEDs are on?3. Do you have a 0.1uF or greater decoupling capacitor local to each TLC5916?4. Have you tried a lower multiplexing frequency, say 10KHz?
btw if you run the setup from 12V then you will dissipate far too much power in the TLC5916s, and I would expect the overtemperature detection will trip in very quickly when you are lighting all the LEDs. Even at 5V, the voltage at their outputs when they are sinking 100mA could be more than 2V, at which the dissipation in each would be 1.6W