SCL

SDA

ADR

VDD

FILT

I

2

CVDD

I

2

CVDD

J1

extVDD

I

2

C Interface

6 Pin Header

VDD

RGB LED

RED

GREEN

BLUE

LED1

LED2

LED3

1 PF

Cfilt

Cs

0.1 PF

LED

CURRENT

CONTROL

AUDIO

SYNC

FILTER

CONTROL

INTERFACE

PWM

RANDOMIZER

VDD

GND

LGND

Ci1

Ci2

Ci3

0.22 PF

0.22 PF

0.22 PF

MIN

LIN

RIN

LED1

LED2

LED3

LM4970

SNVS312D – JANUARY 2005 – REVISED MAY 2013

www.ti.com

I

2C PATTERN MODE

The LM4970 features an I2C pattern mode for applications where direct control of the LED outputs is required.

I2C pattern mode is activated by setting the I2C_SEL bit in the Pattern Select Register. The LED1 output duty

cycle can be programmed to 100% by setting the I2C_LED1 bit in the Pattern Select Register. Clearing the

I2C_LED1 bit sets the LED1 output duty cycle to 0%. The LED2 output duty cycle can be programmed to 100%

by setting the I2C_LED2 bit in the Pattern Select Register. Clearing the I2C_LED2 bit sets the LED2 output duty

cycle to 0%. The LED3 output duty cycle can be programmed to 100% by setting the I2C_LED3 bit in the Pattern

Select Register. Clearing the I2C_LED3 bit sets the LED3 output duty cycle to 0%. Color LEDs driven at 100%

duty cycle are fully on, and driven at 0% duty cycle are fully off.

PWM FREQUENCY

The PWM frequency of the color LED drivers is programmed through the PWM_F<1:0> bits of the Frequency

Select Register. The LM4970 features four different PWM frequency settings: 15kHz, 60Hz, 7Hz, and 4Hz. PWM

frequency is analogous to the sampling rate of the audio input signal. A higher PWM frequency setting will result

in a more accurate LED representation of the audio input signal in the audio synchronization mode. However, a

PWM frequency that is set too high will decrease the ON time of the LED which will result in reduced LED

intensity. A PWM frequency setting of 60Hz results in an optimal balance between LED accuracy and intensity.

DRIVING RGB LED MODULES

The LM4970’s PWM LED outputs can be used to drive individual color LEDs or RGB LED modules. When

driving RGB LED modules in audio synchronization mode, the color and intensity of the RGB LED module will be

dependent on the audio input signal. In I2C pattern mode, the RGB LED module can be set to any of seven

distinct colors, based on the status of the I2C_LED1, I2C_LED2, and I2C_LED3 bit settings.

Figure 15. Reference Design Board Schematic

12

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