150 Ps / 6.7 kHz

Combined PWM cycle

1

1

3

2

2

3

ROUT

1111

GOUT

0110

BOUT

1100

Blinking period

ON[6:0]

OFF[6:0]

LED

brightness

SLOPE[3:0]

SLOPE[3:0]

DUTY[3:0]

PWM

current

pulses

Duty increases

Duty decreases

Duty constant

LP3936

SNVS259D – NOVEMBER 2003 – REVISED MAY 2013

www.ti.com

APPLICATION INFORMATION

RGB LED Driver

The RGB driver has three outputs that can independently drive one RGB LED or three LEDs of any kind. User

has control over the following parameters separately for each LED:

• ON and OFF (start and stop time in blinking cycle)

• DUTY (PWM brightness control)

• SLOPE (dimming slope)

• ENABLE (direct enable control)

The main blinking cycle is controlled with 2-bit CYCLE control (0.25 / 0.5 / 1.0 / 2.0s).

Figure 23. RGB PWM Operating Principle

RGB_START is the master enable control for the whole RGB function. The internal PWM and blinking control

can be disabled by setting the RGB_PWM control LOW. In this case the individual enable controls can be used

to switch outputs on and off. RGB_EN input can be used for external hardware PWM control. RGB_EN input can

Recommended maximum frequency of RGB LED external PWM control is 1 MHz.

In the normal PWM mode the R, G and B switches are controlled in 3 phases (one phase per driver). During

each phase the peak current set by external resistor is driven through the LED for the time defined by DUTY

setting (0 µs–50 µs). As a time averaged current this means 0%–33% of the peak current. The PWM period is

150 µs and the pulse frequency is 6.67 kHz in normal mode.

Figure 24. Normal Mode PWM Waveforms at different duty settings

In the FLASH mode all the outputs are controlled in one phase and the PWM period is 50 µs. The time averaged

FLASH mode current is three times the normal mode current at the same DUTY value.

Blinking can be controlled separately for each output. On and OFF times determine, when a LED turns on and off

within the blinking cycle. When both ON and OFF are 0, the LED is on and doesn't blink. If ON equals OFF but is

not 0, the LED is permanently off.

18

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