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Topic: Dimming ZXLD1366 LED Driver via PWM (Read 1 time) previous topic - next topic

Cherubim

Dec 11, 2013, 03:49 pm Last Edit: Dec 11, 2013, 08:41 pm by Cherubim Reason: 1
Hi,

I want to dim my LED and have a LED driver based on the ZXLD1366  IC.

The PWM input voltage of this IC is max 2.5V according to it's datasheet: http://www.diodes.com/datasheets/ZXLD1366.pdf

Now I thought "that's okay, as long as I don't set PWM above 60 (which should be around the 2.5V) all will be okay".
Well: It wasn't okay and the IC blew :(  =(

What did I do wrong and how exactly will I be able to use PWM with this IC?

Thanks for your help  :)

arduinodlb


The PWM input voltage of this IC is max 2.5V


Where does it say this?
Do not IM me. I will not respond. Ask questions in the forum.

Cherubim


arduinodlb

OK,

So the datasheet says:
Maximum ratings: Vadj = -0.3 - 6VDC.

It also says:
ADJ: Drive with DC Voltage 0.3 < Vadj < 2.5 to adjust from 25% to 200%., with normal operation at 1.25V.

So, I would interpret that as you want to be operating at 1.25V, unless you have a reason to do otherwise. If you were operating at 5V, 60% duty cycle, you're at 3V, which it's not going to like.
Do not IM me. I will not respond. Ask questions in the forum.

Cherubim

Exactly - I already found out the hard way that the IC doesn't like too much voltage :)

arduinodlb

Does that mean your original questions have now been answered?
Do not IM me. I will not respond. Ask questions in the forum.

Cherubim

No, not at all. I know that I need to have max 2.5V - but I don't know how to get there.

fungus


It also says:
ADJ: Drive with DC Voltage 0.3 < Vadj < 2.5 to adjust from 25% to 200%., with normal operation at 1.25V.

So, I would interpret that as you want to be operating at 1.25V, unless you have a reason to do otherwise. If you were operating at 5V, 60% duty cycle, you're at 3V, which it's not going to like.


Variable voltage? That doesn't sound like a PWM input to me. I think the PWM input is the other pin...

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

Cherubim

Well the datasheet says otherwise :)

"Enhanced output current dimming resolution can be achieved by
applying a PWM signal to the 'ADJ' pin. "
"Single pin on/off and brightness control using DC voltage or
PWM "

So it is a combined pin.

fungus


Well the datasheet says otherwise :)

"Enhanced output current dimming resolution can be achieved by
applying a PWM signal to the 'ADJ' pin. "
"Single pin on/off and brightness control using DC voltage or
PWM "

So it is a combined pin.


Oh, I see.

It says "PWM frequency < 300Hz PWM amplitude = VREF Measured on ADJ pin "

So you need a voltage divider to drop 5V down to whatever reference voltage you want.

PS: Arduino PWM frequency is higher then 300Hz so that's another problem you need to solve.

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

arduinodlb


No, not at all. I know that I need to have max 2.5V - but I don't know how to get there.


In this case, it means either a DC voltage of 2.5V Max, or an average PWM voltage of 2.5V Max. This is how you get there:


It also says:
ADJ: Drive with DC Voltage 0.3 < Vadj < 2.5 to adjust from 25% to 200%., with normal operation at 1.25V.

So, I would interpret that as you want to be operating at 1.25V, unless you have a reason to do otherwise. If you were operating at 5V, 60% duty cycle, you're at 3V, which it's not going to like.


So, for your 5V supply, you want a duty cycle of 1.25/5 = 25%. This will provide an AVERAGE voltage of 1.25V, which is less than the 2.5V MAX.
Do not IM me. I will not respond. Ask questions in the forum.

fungus


So, for your 5V supply, you want a duty cycle of 1.25/5 = 25%. This will provide an AVERAGE voltage of 1.25V, which is less than the 2.5V MAX.


No. The datasheet specifically says the PWM amplitude must be Vref.




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

arduinodlb



So, for your 5V supply, you want a duty cycle of 1.25/5 = 25%. This will provide an AVERAGE voltage of 1.25V, which is less than the 2.5V MAX.


No. The datasheet specifically says the PWM amplitude must be Vref.



Hmmm. You're right. That seems odd.
Do not IM me. I will not respond. Ask questions in the forum.

Cherubim

Thanks for your posts.
As you see, this isn't an easy matter - at least when you only know the basic electronics stuff like me :(
I can programm my arduino, but when it comes to things like that, I'm overchallenged.

fungus



No. The datasheet specifically says the PWM amplitude must be Vref.


Hmmm. You're right. That seems odd.


There's nothing "odd" about it. It was probably a case of do it that way or add more pins to the chip.

You can set the PWM amplitude with two resistors. No big deal.
No, I don't answer questions sent in private messages (but I do accept thank-you notes...)

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