LP3954TLXSLASHNOPB datasheet(14/58 Pages) TI2

14 / 58 page

LP3954

SNVS340D – JUNE 2005 – REVISED MARCH 2013

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Ext. PWM Control(1)

wled1-4_pwm

bit 7

PWM controls WLED 1-4

wled5-6_pwm

bit 6

PWM controls WLED 5-6

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

HC_Flash

hc_pwm

bit 5

PWM controls high current flash

(1)

Note: If DISPL=1, wled1-4pwm controls WLED1-6

Note: Maximum external PWM frequency is 1kHz. If during the

external PWM control the internal PWM is on the result will be

product of both functions.

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

100 - internal current mirror multiplier

RRGB- resistor value in Ohms

Ω - internal resistor in the IRGB input

For example if 22mA is required for maximum RGB current RRGB equals to

RRGB = 100 × 1.23V / IMAX –50Ω = 123V / 0.022A –50Ω = 5.54kΩ

(2)

Each individual RGB output has a separate maximum current programming. The control bits are in registers

RGB1 max current and RGB2 max current (12H and 13H) and programming is shown in table below. The

default value after reset is 00.

IR1[1:0], IG1[1:0],

Maximum

IB1[1:0], IR2[1:0],

Current/Output

IG2[1:0], IB2[1:0]

0.25 × IMAX

0.50 × IMAX

0.75 × IMAX

1.00 × IMAX

SWITCH MODE

The switch mode is used if there is a need to connect parallel LEDs to output or if the RGB output current needs

to be increased.

Please note that the switch mode requires an external ballast resistors at each output to limit the LED current.

The switch/current mode and on/off controls for RGB are in the RGB_ctrl register (00H) as follows:

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