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TLC5947 - Higher output current

Hecklebone
Prodigy 10 points
Other Parts Discussed in Thread: TLC5947

Hello all, I am a neophyte to this, so please be kind to the noob.

I am interfacing with a series of 6 TLC5947s.  I'm using a PIC to send the 288 bits for 24 outputs over SPI for each 5947.  I have chosen the 5947 because it is a simple matter to connect them with SPI and the density of 24 outputs v. the more common 16.
I would like to drive more powerful LEDs, up to 1a peak per output.
I was trying a NPN BJT and a n-channel fet...but am getting confused because the 5947 outputs are active low.

I would like to just treat the TLC5947 outputs as an PWM input signal to a power amplifier than can handle the larger current.
Does this approach make sense?
Do I just need to switch to a p-channel fet or PNP BJT?

Thank you in advance!

Heckle. 

 

  • 0
    TI__Mastermind 36110 points

    Be aware that the TLC5947 is not designed to be fully SPI compliant.  The TLC5947 datasheet describes the timing requirements in detail, so please review these.   You can use the any of the methods you describe above.  If you use npn or n-ch devices, your LEDs will turn off when the TLC5947 LED driver turns on.  If you use pnp or p-ch devices, your LEDs will turn on when the TLC5947 turns on.  Note that if you use the discrete FET or transitor to drive your LEDs, you loose the very accurate current control provided by the TLC5947.  Your current accuracy becomes a function of your discrete component characteristics.