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# TLC59116 driving LEDs in Series

Other Parts Discussed in Thread: TLC59116, TLC59116EVM-390

I have selected LED driver TLC59116 for driving Tricolor LEDs. I have seen the evaluation board TLC59116EVM-390 and trying to use the same design, selected the same LEDs too, but will be using two LEDs in series for each line. One signal will be driving two LEDs of same color. I have a few doubts on this. Could someone please clarify?

1. The LEDs are rated with maximum 20mA forward current. The evaluation board is designed with 19mA. Is this the maximum current or minimum current? When we select different colors, will this current increase or decrease? I was thinking to set the current around 10mA and maximum to 20mA by a series resistor. I need to create around 15different colors from the TriColor LEDs.
2.  Since the maximum forward voltage of each LED is around 4.1V, the VLED voltage should be over 8.2V. I have selected 12V with a series resistor for dissipating the extra power. Is this fine? Otherwise I can use 9V/10V to reduce the power dissipation with/without the series resistor?
3. What will be the power dissipation? For two LEDs with 4V forward voltage and 20mA current driving from 12V, will it be 12V * 20mA = 240mW?

Thanks & Regards

Sareesh

• Hi Sareesh,

Thanks for reaching out. I'm going to assume you are using the i version of the TLC59116 (has a single REXT resistor to set the current of the LEDS).

The answers I provide can be explained in more depth in the datasheet. This will also help you to understand how flexible you can be with the design constraints.

The REXT resistor sets the original reference current for the device. Without changing the output current register, the value of the output current will be within +-8% of the expected value (Datasheet section 7.5 and 10.2.2). To create the colors, it's easier to use the PWM registers to dim the red, green, and blue LEDs.

There is an output gain control register that's available in order to change this value. This is useful for analog dimming of all of the channels (Datasheet section 9.5.9).

For power dissipation, please refer to section 12.3 in the datasheet. As a rule of thumb, you want to have at least 1V on the output of the channel. Section 7.7 shows how output current changes based off the output voltage.

Please let me know if you have any questions after reading the sections.