lp5526tlx National Semiconductor Corporation, lp5526tlx Datasheet - Page 14

• Manufacturer Part Number: lp5526tlx
• Description: Lighting Management Unit With High Voltage Boost Converter With Up To 150ma Serial Flash Led Driver
• Manufacturer: National Semiconductor Corporation

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Functionality of Color LED
Outputs (RLED, GLED, BLED)
Switch Mode / Constant Current Mode
Each RGB LED output can be set to act as a switch or a
constant current sink. Selection of mode is done with the
CC_SW bit in the Control Register. If bit is set high, then the
switch mode is selected. Default is switch mode.
SWITCH MODE
In switch mode, the RGB LED outputs are low ohmic
switches to ground. Resistance is typically 3.2Ω. External
ballast resistors must be used to limit the current
through the LED.
CONSTANT CURRENT MODE
In constant current mode, the maximum output current is
defined with a single external resistor (R
mum current control register (address 02H).
Maximum current for each LED output is adjusted with the
RGB max current register in following way:
External ballast resistors are not needed in this mode. The
maximum current for all RGB LED drivers is set with R
The equation for calculating the maximum current is:
where
I
constant current mode)
1.23V = reference voltage
100 = internal current mirror multiplier
R
50 Ω = Internal resistor in the I
MAX
(Continued)
IG[1:0]
RGB
IR[1:0]
IB[1:0]
Name
IR[1:0], IG[1:0], IB[1:0]
= maximum RGB current in any RGB output (during
= resistor value in Ohms
RGB MAX CURRENT REGISTER (02H)
I
MAX
5:4
3:2
1:0
Bit
00
01
10
11
= 100 x 1.23V / (R
GLED maximum current
RLED maximum current
BLED maximum current
Maximum current / output
RGB
Description
RGB
input
0.25 x I
0.50 x I
0.75 x I
1.00 x I
+ 50 Ω)
RGB
) and the maxi-
MAX
MAX
MAX
MAX
RGB
.
14
Table with example resistance values and corresponding
output currents:
Note that the LED output requires a minimum saturation
voltage in order to act as a true constant current sink. The
saturation voltage minimum is typically 230mV defined with
10% current drop. If the LED output voltage drops below
230mV, then the current will decrease significantly.
3. EXTERNAL PWM CONTROL
The GPIO[0]/PWM pin can be used to control the RGB
output brightness or set RGB leds on/off. PWM function for
the pin is selected by writing EN_PWM_PIN high in GPIO
control register (address 06H). Note, that EN_RGB bit must
be set high. Each LED output can be enabled with RSW,
GSW and BSW bits. EN_EXT_R_PWM, EN_EXT_G_PWM
and EN_EXT_B_PWM bits are used to select, which LED
outputs are controlled with the external PWM input. Note that
polarity of external PWM control is active high i.e. when pin
is in high state, then LED output is enabled. If RGB_PWM is
set low, then each selected LED output is controlled directly
with external PWM input. If RGB_PWM is set high, then
internal PWM control is modulated by the external PWM
input. In latter case, internal PWM control is passed to LED
when external PWM input is high.
RGB resistor R
2.4
2.7
3.0
3.3
3.6
3.9
4.3
4.7
5.1
5.6
6.2
RGB
(kΩ)
Maximum current / output
I
MAX
50.2
44.7
40.3
36.7
33.7
31.1
28.3
25.9
23.9
21.8
19.7
(mA)