LP3952 datasheet(12/46 Pages) TI1

12 / 46 page

LP3952

SNVS518A – JULY 2007 – REVISED MARCH 2013

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FUNCTIONALITY OF COLOR LED OUTPUTS (R1, G1, B1; R2, G2, B2)

The LP3952 has 2 sets of RGB/color LED outputs. Both sets have 3 outputs and the sets can be controlled in 4

different ways:

1. Command based pattern generator control (internal PWM)

2. Audio synchronization control

3. Programmable ON/OFF blinking sequences for RGB1

4. External PWM control

By using command based pattern generator user can program any kind of color effect patterns. LED intensity,

blinking cycles and slopes are independently controlled with 8 16-bit commands. Also real time commands are

possible as well as loops and step by step control. If analog audio is available on system, the user can use

audio synchronization for synchronizing LED blinking to the music. The different modes together with the

various sub modes generate very colorful and interesting lighting effects. Direct ON/OFF control is mainly for

switching on and off LEDs. External PWM control is for applications where external PWM signal is available

and required to control the color LEDs. PWM signal can be connected to any color LED separately as shown

later.

COLOR LED CONTROL MODE SELECTION

The RGB_SEL[1:0] bits in the Enables register (08H) control the output modes for RGB1 (R1, G1, B1) and RGB2

(R2, G2, B2) outputs as seen in the following table.

RGB_SEL[1:0]

Audio sync

Pattern generator

Blinking control

RGB1 & RGB2

RGB2

RGB1

RGB2

RGB1

RGB1 & RGB2

RGB Control register (00H) has control bits for direct on/off control of all color LEDs. Note that the LEDs have

to be turned on in order to control them with audio synchronization or pattern generator.

The external PWM signal can control any LED depending on the control register setup. External PWM signal is

connected to PWM pin. The controls are in the Ext. PWM Control register (address 07H):

Ext. PWM Control (07H)

r1_pwm

bit 5

PWM controls R1 output

g1_pwm

bit 4

PWM controls G1 output

b1_pwm

bit 3

PWM controls B1 output

r2_pwm

bit 2

PWM controls R2 output

g2_pwm

bit 1

PWM controls G2 output

b2_pwm

bit 0

PWM controls B2 output

CURRENT CONTROL OF COLOR LED OUTPUTS (R1, R2, G1, G2, B1, B2)

Both RGB output sets can be separately controlled as constant current sinks or as switches. This is done using

cc_rgb1/2 bits in the RGB control register. In constant current mode one or both RGB output sets are controlled

with constant current sinks (no external ballast resistors required). The maximum output current for both drivers

is set by one external resistor RRGB. User can decrease the maximum current for an individual LED driver by

programming as shown later.

The maximum current for all RGB drivers is set with RRGB. The equation for calculating the maximum current is:

IMAX = 100 × 1.23V / (RRGB + 50Ω)

(1)

where:

IMAX - maximum RGB current in any RGB output in constant current mode

1.23V - reference voltage

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