LP3936 Datasheet, PDF (19/30 Pages) National Semiconductor (TI) – Lighting Management System for Six White LEDs and One RGB or FLASH LED

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LP3936
SNVS259D – NOVEMBER 2003 – REVISED MAY 2013
ROUT
ON<OFF
ON
GOUT
OFF
OFF
ON
OFF<ON
ON
OFF
OFF
ON
BOUT
ON=OFF=0
First cycle
Next cycles
Figure 25. Example Blinking Waveforms
RGB Driver Electrical Characteristics
(R_OUT, G_OUT, B_OUT outputs)
Symbol
Parameter
Conditions
R_DS-ON
I_LEAKAGE
I_MAX
T_SMAX
T_SMIN
T_SRES
T_START/STOP
Duty
ON Resistance
Off State Leakage Current
Maximum Sink Current
Maximum Slope Period
Minimum Slope Period
Slope Resolution
Start/Stop Resolution
Duty Step Size
V_FB = 5.3V
See ⁽¹⁾
Maximum Duty Setting
Maximum Duty Setting
Maximum Duty Setting
Cycle 1s
T_BLINK
D_CYCF
D_CYC
D_RESF
D_RES
F_PWMF
F_PWM
Blinking Cycle Accuracy
Duty Cycle Range
Duty Cycle Range
Duty Resolution
Duty Resolution
PWM Frequency
PWM Frequency
EN_FLASH = 1
EN_FLASH = 0
EN_FLASH = 1 (4-bit)
EN_FLASH = 0 (4-bit)
EN_FLASH = 1
EN_FLASH = 0
(1) The total load current of the boost converter should be limited to 250 mA.
RGB LED PWM Control⁽²⁾
Min
Typ
Max
Units
2
4.5
Ω
0.04
1
µA
120
mA
0.93
s
31
ms
62
ms
1/16
s
1/16
−6
±3
+6
%
0
94
%
0
31
%
6.27
%
2.09
%
20
kHz
6.67
kHz
RDUTY[3:0]
GDUTY[3:0]
BDUTY[3:0]
RSLOPE[3:0]
GSLOPE[3:0]
BSLOPE[3:0]
RON[6:0]
GON[6:0]
BON[6:0]
ROFF[6:0]
GOFF[6:0]
BOFF[6:0]
DUTY sets the brightness of the LED by adjusting the duty cycle of the PWM driver. The minimum DUTY cycle [0000]
is 0% and the maximum [1111] in the Flash mode is 94% and in the normal mode 31% of the peak pulse current. The
peak pulse current is determined by the external resistor, LED forward voltage drop and the boost voltage.
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 50% DUTY [1000] the sloping time
is 17 ms [0000] to 496 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 = 0–127) sets the on-time to N/128 * 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), DUTY controls the
brightness and SLOPE is ignored.
If ON and OFF are the same, but not 0, RGB outputs are turned off.
(2) TI's AN-1293 Driving RGB LEDs Using LP3936 Lighting Management System Application Report (SNVA071) contains a thorough
description of the RGB driver functionality including programming examples.
Copyright © 2003–2013, Texas Instruments Incorporated
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