LP3950 Datasheet, PDF (21/38 Pages) National Semiconductor (TI) – Color LED Driver with Audio Synchronizer

LP3950
www.ti.com
SNVS331C – NOVEMBER 2004 – REVISED APRIL 2013
Table 3. RGB LED PWM Control ⁽¹⁾
RDUTY[3:0]
GDUTY[3:0]
BDUTY[3:0]
RSLOPE[3:0]
GSLOPE[3:0]
BSLOPE[3:0]
RON[3:0]
GON[3:0]
BON[3:0]
ROFF[3:0]
GOFF[3:0]
BOFF[3:0]
ROFF[3:0]
GOFF[3:0]
BOFF[3:0]
CYCLE[2:0]
RSW1
GSW1
BSW1
RSW2
GSW2
BSW2
RGB_START
RGB_PWM
EN_FLASH
R1_PWM
G1_PWM
B1_PWM
R2_PWM
G2_PWM
B2_PWM
DUTY sets the brightness of the LED by adjusting the duty cycle of the PWM driver. The minimum DUTY cycle is 0%
[0000] and the maximum in the flash mode is 100% [1111]. The peak pulse current is determined by the external
resistor, LED forward voltage drop and the boost voltage. In the normal mode the maximum duty cycle is 33%.
SLOPE sets the turn-on and turn-off slopes. Fastest slope is set by [0000] and slowest by [1111]. SLOPE changes the
duty cycle at constant, programmable rate. For each slope setting the maximum slope time appears at maximum
DUTY setting. When DUTY is reduced, the slope time decreases proportionally. For example, in case of maximum
DUTY, the sloping time can be adjusted from 31 ms [0000] to 930 ms [1111]. For DUTY [0111] the sloping time is 14
ms [0000] to 434 ms [1111]. The blinking cycle has no effect on SLOPE.
ON sets the beginning time of the turn-on slope. The on-time is relative to the selected blinking cycle length. On-
setting N (N = 0–15) sets the on-time to N/16 * cycle length.
OFF sets the beginning time of the turn-off slope. Off-time is relative to blinking cycle length in the same way as on-
time.
If ON = 0, OFF = 0 and RGB_PWM = 1, then RGB outputs are continuously on (no blinking), the DUTY setting
controls the brightness and the SLOPE control is ignored.
If ON and OFF are the same, but not 0, RGB outputs are turned off.
CYCLE sets the blinking cycle: [000] for 0.25s, [001] for 0.5s, [010] for 1.0s, [011] for 2.0s. and [1XX] for 4.0s CYCLE
effects to all RGB LEDs.
Enable for R1 switch
Enable for G1 switch
Enable for B1 switch
Enable for R2 switch
Enable for G2 switch
Enable for B2 switch
Master Switch for both RGB drivers:
RGB_START = 0 → RGB OFF
RGB_START = 1 → RGB ON, starts the new cycle from t = 0
RGB_PWM = 0 → RSW, GWS and BSW control directly the RGB outputs (on/off control only)
RGB_PWM = 1 → Normal PWM RGB functionality (duty, slope, on/off times, cycle)
Flash mode enable control for RGB1 and RGB2. In the flash mode (EN_FLASH = 1) RGB outputs are PWM controlled
simultaneously, not in 3-phase system as in the normal mode.
xx_PWM = 0 → External PWM control from PWM_LED pin is disabled
xx_PWM = 1 → External PWM control from PWM_LED pin is enabled
Internal PWM control (DUTY) can be used independently of external PWM control. External PWM has the same effect
on all enabled outputs.
(1) The LP3933 shares the same pattern generator. Application Note AN-1291 (SNVA069), “Driving RGB LEDs Using LP3933 Lighting
Management System” contains a thorough description of the RGB driver functionality including programming examples.
PWM_LED input can be used as a direct on/off or PWM brightness control for selected RGB outputs. For
example it can trigger the flash using a flash signal from the camera. If PWM_LED input is not used, it must be
tied to V_DDIO.
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