LP5815: Can it be configured to use with a common cathode RGB LED?

Bill Johnson

Part Number: LP5815

Tool/software:

I can't seem to find a panel mount RGB LED with a common anode configuration. What I have found seems to be all common cathode. The LP5815 is a sinking configuration. Is it possible to use a pull-up resistor to 5V on each pin and connect the anode of the LED's to the each pin? Therefor, if it is PWM driving the pin, during a low the LED is off and during a high the LED is on. Basically, an inverse relationship to the PWM.

3 months ago

0 Felix Wang 3 months ago

TI__Expert 5860 points

Hi Bill,

Yes, you can use that method to turn on and off the LED, but the current is not controlled constantly.

Actually we have the current source LED driver that is appropriate for driving common cathode LEDs. Could you help to answer the questions below? then i will have the recommendation.

How many leds are your want to control? How much is the current for each led? and what's the dimming method required? Direct PWM dimming or through digital interface (i2c or spi, ect.)?

Best regards,

Felix

0 Bill Johnson 3 months ago in reply to Felix Wang

Prodigy 10 points

Thank for getting back to me.

We are controlling 3 Led's (R,G,B). We are using a panel mount Led and the datasheet is a bit vague so I don't know if a resistor is embedded. The datasheet does mention 15mA but that doesn't say per Led or not. I'm incorporating resistors myself (150,100,100 respectively) with a 3.3V supply. I have tested the circuit and these values are fine. The I2C command can control the dimming. So if I want orange, for instance, I would give it an I2C command and it would set up the registers for let's say (255,128,0) and then I give it a command for let's say 50% dimming. Then all it would set all values by 50%. I hope I answered your questions correctly.

Thanks,

Bill

+1 Felix Wang 3 months ago in reply to Bill Johnson

TI__Expert 5860 points

Hi Bill,

Recommend to take a look at the LP5812, 4 x 3 matrix RGB LED driver with I2C and auto animation control.

You can use the single chip without additional pull up resistors to realize the common cathode RGB led driver control with constant current control based on the configuration below.

Best regards,

Felix

0 Bill Johnson 3 months ago in reply to Felix Wang

Prodigy 10 points

Thanks Felix! I'm incorporating this into my design. Is it required to hook up the LED's in the color pattern as shown? Meaning; does Blue have to go to OUT0, Red to OUT1, and Green to OUT2? Or are these interchangeable?

+1 Felix Wang 3 months ago in reply to Bill Johnson

TI__Expert 5860 points

Hi Bill,

No, you can place the R/G/B in you own order.

Best regards,

Felix

0 Bill Johnson 3 months ago in reply to Felix Wang

Prodigy 10 points

Hi Felix,

Thanks for the quick response. The reason I asked is because I was looking at Table 7-1 and the Note right below it states "To avoid unexpected emitting, in RGB LEDs applications, Red LEDs are recommended to be placed in LED_x1 (x=A, B, C, D) positions."