LP3936 Datasheet, PDF (16/20 Pages) National Semiconductor (TI) – Lighting Management System for Six White LEDs and One RGB or FLASH LED

RGB LED Driver (Continued)
In the FLASH mode all the outputs are controlled in one
phase and the PWM period is 50 µs. The time averaged
FLASH mode current is three times the normal mode current
at the same DUTY value.
Blinking can be controlled separately for each output. On
and OFF times determine, when a LED turns on and off
within the blinking cycle. When both ON and OFF are 0, the
LED is on and doesn’t blink. If ON equals OFF but is not 0,
the LED is permanently off.
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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
(Note 12)
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
Note 12: The total load current of the boost converter should be limited to 250 mA.
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
RGB LED PWM Control (Note 13)
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 A 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.
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