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TLC5947 Interfacing with a FPGA

Miguel Ferreira
Prodigy 30 points
Other Parts Discussed in Thread: TLC5947

Hi,

In my design I'm using 22 TLC5947, they are controlled by a FPGA, I want to put a buffer in the control lines,

can you please  advise me  one buffer I'll operate the TLC5947 at low frequency Khz..

I´ll have 20 Led @ 3V3 0,6mA in total per chip, what is the best value an how many cap are necessary for the led bulk capacitor.

Regards,

Miguel

 

 

 

  • 0
    TI__Mastermind 36110 points

    There are no special requirements for a buffer if one is used between the FPGA and the TLC5947 LED driver.  You can buy a standard buffer or you can make your own from an opamp.

    The required bulk capacitance is a function of how much voltage ripple you can allow in your system.  If you assume that the bulk capacitor supplies all the current for each current pulse, the required capacitance is C=i*t/V where

    i is the current through the LEDs

    V is is the maximum allowable voltage drop

    t is the time that the LEDs are on

    The actual voltage drop will be less than calculated because the LED power supply will supply much of the LED current.  The bulk capacitance supples the currents at turn on and turn off