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[SpiROSE] LED driver choice

Last time we discussed how multiplexing reduces power consumption and the number of driver, hence reduces the space constraints. This leads to several consequences:

  • The more we multiplex, the more bandwidth is required from the driver
  • Doing n-multiplexing divides the LEDs’ intensity by n, this can be fixed with a bit of overdrive (we can go up to 8 times the intensity)
  • If a driver controls n rows (or columns) they will be staggered because they are displayed one after another

Thus we made some computations to choose a suitable driver and multiplexing.

The two competitors were TLC5957 and TLC59581, the first one can go up to 33 MHz and send from 9 to 16 bit per color with only 1 buffer per bank, the second one can go up to 25 MHz and send 16 bit per color with n buffer per bank, where n is the multiplexing. The second one is interesting because it could do multiplexing without sending back data thanks to the several buffers.

So for each multiplexing we computed the required bandwidth, the nominal power with and without overdrive, and obtained the following output:

 

Multiplexing TLC5957 bandwidth (MHz) TLC59581 bandwidth (MHz) Nominal power (W) Nominal power with x8 overdrive (W)
2 6,79 12,07 88,7685 710,148
4 13,58 24,14 44,38425 355,074
8 27,16 48,28 22,192125 177,537
16 54,32 96,56 11,0960625 88,7685
32 108,64 193,12 5,54803125 44,38425

 

Thus the best trade off is with the 8 multiplexing and the TLC5957 because we can’t do more than 4-multiplexing with the other one.

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