LP3950

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SNVS331C – NOVEMBER 2004 – REVISED APRIL 2013

RDUTY[3:0]

DUTY sets the brightness of the LED by adjusting the duty cycle of the PWM driver. The minimum DUTY cycle is 0%

GDUTY[3:0]

[0000] and the maximum in the flash mode is 100% [1111]. The peak pulse current is determined by the external

BDUTY[3:0]

resistor, LED forward voltage drop and the boost voltage. In the normal mode the maximum duty cycle is 33%.

RSLOPE[3:0]

SLOPE sets the turn-on and turn-off slopes. Fastest slope is set by [0000] and slowest by [1111]. SLOPE changes the

GSLOPE[3:0]

duty cycle at constant, programmable rate. For each slope setting the maximum slope time appears at maximum

BSLOPE[3:0]

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.

RON[3:0]

ON sets the beginning time of the turn-on slope. The on-time is relative to the selected blinking cycle length. On-

GON[3:0]

setting N (N = 0–15) sets the on-time to N/16 * cycle length.

BON[3:0]

ROFF[3:0]

OFF sets the beginning time of the turn-off slope. Off-time is relative to blinking cycle length in the same way as on-

GOFF[3:0]

time.

BOFF[3:0]

ROFF[3:0]

GOFF[3:0]

BOFF[3:0]

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[2:0]

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.

RSW1

Enable for R1 switch

GSW1

Enable for G1 switch

BSW1

Enable for B1 switch

RSW2

Enable for R2 switch

GSW2

Enable for G2 switch

BSW2

Enable for B2 switch

RGB_START

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

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)

EN_FLASH

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.

R1_PWM

xx_PWM = 0

→ External PWM control from PWM_LED pin is disabled

G1_PWM

xx_PWM = 1

→ External PWM control from PWM_LED pin is enabled

B1_PWM

Internal PWM control (DUTY) can be used independently of external PWM control. External PWM has the same effect

R2_PWM

on all enabled outputs.

G2_PWM

B2_PWM

(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

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