LED driver with 4 independent outputs

[pedrorito]

Hello.

I'm planning to build a PCB with 4 LEDs. I'm considering to buy the following LED component to use:

https://uk.mouser.com/ProductDetail...hA207qyZW7ztWxGE2YoDZNdI69J8I/hyLroBP%2bT8VRE

I don't know much about brightness levels, but I want something for signalling in dark places, I think the intensity of this one should be enough?

On this PCB I will have a micro-controller and I would like to control each LED independently. I will control the PWM in order to play with the brightness (this could be the same for the 4 LEDs), but I want to switch on or off each one independently - so then I could do something like shifting illuminated LEDs.

What do you think is the best solution for me? I'm searching for LED drivers that could fit my specs. Any suggestion?

I will power the board with batteries, I was considering to use 2x AA battery in series. It's why I must have a driver in order to have constant current driving.
Also because of the battery, a requirement for the driver will be the minimum input supply that should be like 2.5V / 3V maximum.

Thanks. Looking forward for your help.

 

[barry]

Depending on what microprocessor you use, you can possibly drive the LEDS directly-no driver needed(PICs can sink 25 mA). You could use a single transistor as the PWM control for all 4 LEDs.

 

[pedrorito]

I working with low-power MCUs. I'm using one SoC CC2541 8051-based, but I could also use MSP430.

I'm afraid it will be extreme for this MCUs to drive directly the LEDs. I could also use a transistor for each LED, but then I won't guarantee constant current when using batteries.

 

[Audioguru]

You should look at the datasheet from the manufacturer of the LED, not at Mouser's listing.
Two 1.5V battery cells are 3.2V when new and are 2.0V when used but the maximum forward voltage of the LED is 2.5V so some of them WILL NOT WORK for half the life of the battery. The LEDs will get dimmer and dimmer and dimmer and .....

 

[pedrorito]

You should look at the datasheet from the manufacturer of the LED, not at Mouser's listing.
Two 1.5V battery cells are 3.2V when new and are 2.0V when used but the maximum forward voltage of the LED is 2.5V so some of them WILL NOT WORK for half the life of the battery. The LEDs will get dimmer and dimmer and dimmer and .....

I know, It's why I was pointing out the reason I need a driver. It will correct this, no?

 

[barry]

I thought you were going to use PWM to control brightness?

 

[pedrorito]

I thought you were going to use PWM to control brightness?

Only if there was a driver with that possibility. It is not mandatory. The main requirement would be to switch on each one independently. Because the drivers that I see with 4 channels, the outputs are not independent. They have only one control for all the outputs.

 

[Audioguru]

I know, It's why I was pointing out the reason I need a driver. It will correct this, no?

An LED driver will limit the current and have some voltage loss, it will not boost the voltage. You might need to use three or four battery cells.

 

[pedrorito]

Thanks for your help.

About battery, like Audioguru said, maybe in the end I will need more than 2x AA batteries, but I think it's not the main issue by now. I would be able to adapt in the end.

The main issue is which is best driver in order to play with my parallel array of LEDs, with constant current driving and using less number of pins from the MCU.

I found this LED Driver from TI:

https://www.ti.com/product/lp55231

What do you think? I can control everything using I2C communication: PWM and enabling each LED independently.
It is provided 9 outputs (more than the 4 that I need) but maybe is a good thing for the initial steps. Because I'm not sure which LED I should use to have all the brightness that I need, later on if I need more than 25mA for each LED (that is the current provided from each output), I can connect every LED to 2 outputs.