Dimming ZXLD1366 LED Driver via PWM

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 :)

Cherubim: The PWM input voltage of this IC is max 2.5V

Where does it say this?

In the datasheet :) VADJ 0.3 -2.5V

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.

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

Does that mean your original questions have now been answered?

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

arduinodlb:
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…

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.

Cherubim:
Well the datasheet says otherwise :slight_smile:

"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.

Cherubim:
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:

arduinodlb:
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.

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.

fungus:

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.

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.

arduinodlb:

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.

fungus:

arduinodlb:

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.

Well, that’s a matter of opinion.

I'm now successfully using a BC547 transistor with a 4k7 Ohm base resistor to dim the LEDs. This is working perfectly fine, with 122Hz timers or the default 490Hz ones.