TTP223 as sink or source

Using Arduino General Electronics
1

First I'd like you to excuse me if this is a very basic question but I'm just a beginner.

I'd like to reduce the brightness of a led that indicates me that a circuit which is activated by a TTP223 board is in stand-by mode. I do this indication using the TTP's output as sink.

But in this topic I've found that post:

"IOH is spec'ed as VDD=3V and VOH=2.4V means you can pull -4 ma out of the pin, maximum. This would be current pulled through the device, out the pin, into your load. This would be what you'd get if you attached a resistor from the output pin to gnd.

The IOL spec is higher at 8 ma which means it can absorb more than it can push. Think of a resistor with one end to the output pin, the other end attached to VDD.

Not that you'd do this, but you could calculate the maximum values for your resistors this way:

Sourcing: IOH=-4ma, VOH=2.4. R=E/I so 2.4/.004 = 600 ohms

Sinking: IOL=8ma when VDD=3V, VOL=0.6V. VDD-VOL=2.4V/.008 = 300 ohms"

In my case the calculation is:

VDD=5v, VOL=0.6 ; VDD-VOL=4.4v ; 4.4/0.008 = 550 ohm

But I've got the ideal led's brightness with a 2k2 ohm resistor...

May I use this 2k2 resistance for that?

And just trying to understand this TTP's sink resource, as merely curiosity, as the recommend resistor for this led is 140 ohm (as calculated here), if I use less resistance than the 550 ohm, could that demage the chip?

Thank you.

2

I should not have to google TTP223.
You should post a link.
If you know Ohm's Law you can answer your question.
E=IR | where E=V
P=IE | where E= V

Why are you asking if you can use MORE than
the recommended resistance ?
Do you need our permission to do that ?
I could understand asking about the risk of
using LESS resistance, but not more.
Think about it. You are obviously smart, but
reluctant to use your brain. What is the risk of
using more resistance ? If you can tell me that
then you will understand why I am asking because I am not seeing any risk.
If you post a link to the TTP223 then I can confirm that.
If the chip can only source 8mA, how can a 140
ohm resistor change that ?
It is what it is.

3

TTP223 datasheet.
Clearly a 2k2 resistor will be just fine.

The parameters mentioned are specified at 3 V, not 5 V, so that would make some difference, however no absolute maximum values are specified. Certainly you want to keep the current under the values cited.

The common module available has a led on it with what appears to be a 120 Ohm resistor (thought that page gives it as 1k on the schematic)! :woozy_face:

4

Excuse the missing datasheet. Actually I got a little confused because the commercial name of the board is the same name as the chip. But the board is exactly as @Paul_B brought, that little red board.

I've ripped out this led and it's 120 ohm resistor to bring them to the "gadget" panel. I've changed the new resistor's value to 1k but without confidence... as I said, I'm just a beginner and I really don't know what can have inside the chips. That's why I decided to ask who know more than me.

Thank you, that's the answer.

Thank you too, @raschemmel , for the compliment and incentive. Now about the risk... this doubt can occurs when one doesn't know the fundamentals, like beginners. I promise you I'll study more.

Thank you both.

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