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### Topic: [SOLVED] TLC 5940 Max current sink. (Read 1 time)previous topic - next topic

#### AJB2K3

##### Mar 30, 2013, 09:58 amLast Edit: Mar 30, 2013, 12:49 pm by AJB2K3 Reason: 1
Apologies in advance but I'm scratching my head over the data sheet.

I am planning on running this on a 3.6V circuit and my prototype scrolls through 15 20mA led's.
Will this chip be able to handle running 4 led's on each pin? (80mA?) while (on rare occasion) fade all 60?

Sorry but i'm having (whats know in the UK) a blond moment here.
Sorry for the noobish post but my knowledge is 10 years out of date!

#1
##### Mar 30, 2013, 10:11 am

Forward voltage of the LEDs?

Voltage of the LED power supply?  3.6V?

#### AJB2K3

#2
##### Mar 30, 2013, 10:38 am

Forward voltage of the LEDs?

Voltage of the LED power supply?  3.6V?

Well my led's are 20mA each 3.2-3.V @ 20mA total per pin load = 80mA!
Sorry for the noobish post but my knowledge is 10 years out of date!

#### fungus

#3
##### Mar 30, 2013, 12:08 pm

I am planning on running this on a 3.6V circuit and my prototype scrolls through 15 20mA led's.
Will this chip be able to handle running 4 led's on each pin? (80mA?) while (on rare occasion) fade all 60?

The datasheet says:

60 mA (VCC < 3.6 V)
120 mA (VCC > 3.6 V

It doesn't say what happens when VCC=3.6V but 80mA is right in the middle...

You're planning on having the chip dissipate about 0.5V per channel (3.6 minus 3.1). 0.5V*80mA*16 channels=640mW. That's well within the limits for power dissipation.

You should be fine.
No, I don't answer questions sent in private messages (but I do accept thank-you notes...)

#### AJB2K3

#4
##### Mar 30, 2013, 12:49 pm

I am planning on running this on a 3.6V circuit and my prototype scrolls through 15 20mA led's.
Will this chip be able to handle running 4 led's on each pin? (80mA?) while (on rare occasion) fade all 60?

The datasheet says:

60 mA (VCC < 3.6 V)
120 mA (VCC > 3.6 V

It doesn't say what happens when VCC=3.6V but 80mA is right in the middle...

You're planning on having the chip dissipate about 0.5V per channel (3.6 minus 3.1). 0.5V*80mA*16 channels=640mW. That's well within the limits for power dissipation.

You should be fine.

Thanks fungus
Sorry for the noobish post but my knowledge is 10 years out of date!

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