Mulitiple LEDs on TLC5940 pin

Is it possible to use multiple LEDs in series on each pin of the TLC5940? I've tried this and they appear dimmer than single LEDs on the pins next to them.

I tried changing IREF to a lower resistor, but as I understand it from the datasheet, this is supposed to control the current going through the LEDs and I think this is a voltage problem, not current. Changing IREF didn't brighten the 2 LEDs in series, but did brighten the single LEDs on other pins.

Is it possible to have multiple LEDs on each pin? I'm just looking to have 2 LEDs in series on each pin to give a more even glow to my project items. I won't be mixing and matching 1 vs. 2 LEDs. It'll only be 2 LEDs/pin.

Upon further investigation, I have stumbled upon the document "Using TLC5940 With Higher LED Supply Voltages and Series LEDs". I assume this will answer my questions.

Sorry for the duplicate question!

Looks like they suggest using a MOSFET on each pin, but this won't work due to space restrictions. I have to use almost all the pins in my project. Is there a simpler solution? It's only 2 LEDs/channel.

The data sheet says you can have up to a 17v LED supply, that's maybe 7-8 LEDs depending on the forward voltage of the LEDs you're using, so what is your LED supply? If it's 5v that may explain the problem.

I'm pretty sure I just blew my first chip. I was trying to use a 12V supply, so I'm a little confused.

In the datasheet, it says that the input voltage should be –0.3V to 6V, but the output voltage range can be –0.3V to 18V. So I saw smoke and the whole deal when I connected 12V to VCC.

After thinking about this a bunch, I think I get it. The chip itself will get the 6V, but since the LEDs are connected to a positive line, that positive line can be a different voltage.

I will try using a voltage regulator on my 12V to make sure the chip is powered with less than 6V, while powering the LEDs with the 12V.

After thinking about this a bunch, I think I get it. The chip itself will get the 6V, but since the LEDs are connected to a positive line, that positive line can be a different voltage.

I will try using a voltage regulator on my 12V to make sure the chip is powered with less than 6V, while powering the LEDs with the 12V.

Yep, you got it.

The "input voltage" is the voltage used by the chip's logic, that is normally in the 5v range.

The "output voltage" is the voltage that the output pins can tolerate, it's a bit misleading really because they don't actually "output" any voltage, they just connect the pin to ground.

So you connect the chip's VCC to 5v and the anodes of the LEDs to say 12v, cathodes to the chip.

But NOT 12v to the chip's VCC, that will let the smoke out.

So affectively you need two power supplies, but that's usually easy to do, just use the pre-regulator voltage if it's of a suitable value.