[dorkbotpdx-blabber] another LED array question

[Greg Grunest]

Yeah, that is an awesome chip too.  I also noticed the SMT only packaging
which is kind of a drawback.  Has anyone hand soldered one of those chips
with a thermal pad and been successful?  If so, I may need to ask a favor of
them.   The 8-bit version that comes in dip packaging has a ton of
potential.  I'm going to have to order a couple and see if they drive hobby
servos.  That would ROCK if you could drive 16 servos with two of them all
from a serial line on the Arduino.
 
-----Original Message-----
From: dorkbotpdx-blabber-bounces at dorkbot.org
[mailto:dorkbotpdx-blabber-bounces at dorkbot.org] On Behalf Of Paul Stoffregen
Sent: Monday, December 15, 2008 2:06 PM
To: A discussion list for dorkbot-pdx (portland, or)
Subject: Re: [dorkbotpdx-blabber] another LED array question


> That's an awesome chip!  I'd ask you where you found such a great IC but
you
> might not want to divulge too many of your sources. :)
>   

Eric definitely deserves the "most awesome chip found" award for the 
TLC5947!!!

It even controls the current so you only need 1 resistor for every 24 
LEDs.  Pretty amazing.  12 bit PWM and all done on-chip which is a lot 
less coding that what I suggested!  It only costs $0.45 more per 8 bits 
than the simple shift register.

But it also only comes in a tiny SMT chip with a big thermal pad on the 
bottom.  Since it's acting as all those current limiting resistors too, 
I'm pretty sure you'll need to get those thermal pad well soldered to a 
bunch of vias and a big ground plane or small heatsink on the back side 
of the board.  Then again, figure 11 on page 11 of the datasheets seems 
to say the chip can dissipate quite a lot even in free air, which I find 
pretty hard to believe.  But there is a thermal shutdown circuit that 
kicks in at 162 degrees C.....  maybe a good idea to use lead-free 
solder!  (normal SnPb melts around 180C)

> Have you seen a similar part to the one
> you mentioned but in a 16-bit register?
>   

Nope, though that doesn't mean it's not out there.

But the 8 bit part comes in DIP package which is pretty nice if you're 
going to "experiment" without having to etch/buy a PCB.


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