LP5024: LED RGB color and min out

KJ Liu

Part Number: LP5024

Hi Sir,

May I know what is the min Vo , from the Fig.7 of LP5024 datasheet, is 0.5V ? for example, if LED voltage =2.6, the min VLED is 3.1V.

Secondly, we do the experiment and found out the color will be different when Rref change but in same current setup. For example as below, the color is different, would you please help to share is it normal since we don't have much experience in RGB LED control

RIREF =2.2k with 6.5mA (adjust ADC to get 6.5mA)

RIREF=11k with 6.5mA (adjust ADC to get 6.5mA)

over 5 years ago

0 Kenneth Du over 5 years ago

TI__Genius 14295 points

Yes, you can refer to figure 7 for the min voltage on OUT for different current. 0.5V is enough for most of the cases and if you use 35mA, make it a little higher like 0.6V. The you can get your Vled= Vf+Vmin.

Can you share your shcematic for the Riref change? How do you use different resistor to get same current?

0 KJ Liu over 5 years ago in reply to Kenneth Du

Intellectual 530 points

Hi Sir,

The schematic is just like your EVB and we through the I2C to adjust ADC to get same current out when different RIREF.

0 KJ Liu over 5 years ago in reply to Kenneth Du

Intellectual 530 points

Hi Sir,

The schematic is attached, as i mention before, we adjust the RIREF (2.2k and 11k) but through the through I2C to make the each ch current keep in 8mA and found out the color is slightly different when RGB all be turn on(white). The only different we though is PWM duty and want to know, is it make sense that even the average current of OUT is the same , the color would slightly different when PWM duty is different.

The schematic is as below

0 Kenneth Du over 5 years ago in reply to KJ Liu

TI__Genius 14295 points

So you actually use different Riref to get different current.

In such case it's normal for differnt color in different current. This is because the current in R/G/B affect the color temperature.

So you can set the current first and use the PWM (color and brightness register) to get different color and brightness.

0 KJ Liu over 5 years ago in reply to Kenneth Du

Intellectual 530 points

Hi Kenneth,

No, I use different Riref to get same current out to driver LED through I2C adjustment. it's why i can't understand.

0 KJ Liu over 5 years ago in reply to Kenneth Du

Intellectual 530 points

Hi Kenneth,

No, I use different Riref to get same current out to driver LED through I2C adjustment. it's why i can't understand.

0 Kenneth Du over 5 years ago in reply to KJ Liu

TI__Genius 14295 points

I'm a little confused.

If you use different Riref, you'll get different current.

So what do you mean by "adjust ADC to get 6.5mA/"? I didn't see ADC in your schematic. It seems you use 3.6k to get 19.4mA.

0 KJ Liu over 5 years ago in reply to Kenneth Du

Intellectual 530 points

Hi Kenneth,

My mistake, it should be used MCU to adjust PWN duty (Built in 12 bit PWM generator in LP5024)through I2C.

0 Kenneth Du over 5 years ago in reply to KJ Liu

TI__Genius 14295 points

I got it. You use different Riref.

So the maximum current is not the same and this will affect the color.

But you can still adjust the PWM for R/G/B to get an expected color.

For example, you use 10mA for R/G/B but the Red is too much, then you can use a lower duty cycle for Red.

Please let me know if this solves your question.

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LP5024: LED RGB color and min out